\
EPA-450/3-77-033^
November 1977
INSTRUCTOR'S GUIDE
FOR VEHICLE EMISSIONS
CONTROL TRAINING
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U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
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EPA-450/3-77-033
INSPECTOR'S GUIDE
FOR VEHICLE EMISSIONS
CONTROL TRAINING
by
B.D. Hayes, Project Director
M.T. Maness, Associate Project Director
R.A. Ragazzi, Principal Investigator
Department of Industrial Sciences
Colorado State University
Fort Collins, Colorado 80523
EPA Grant No. T900621-01-0
EPA Project Officer: Bruce Hogarth
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Control Programs Development Division
Research Triangle Park, North Carolina 27711
November 1977
-------
Copies of this publication are available free of charge to Federal employees,
current contractors and grantees, and nonprofit organizations - as supplies
permit - from the Library Services Office (MD-35), Environmental Protection
Agency, Research Triangle Park, North Carolina 27711; or, for a fee, from
the National Technical Information Service, 5285 Port Royal Road, Springfield,
Virginia 22161.
This report was furnished to the Environmental Protection Agency by the
Department of Industrial Sciences, Colorado State University, Fort Collins,
Colorado, 80523, through Grant No. T900621-01-0. The contents of this report
are reproduced herein as received from Colorado State University. The opinions,
findings, and conclusions expressed are those of the authors and not necessarily
those of the Environmental Protection Agency. Mention of company or product
names is not to be considered as an endorsement by the Environmental Protection
Agency.
Publication No. EPA-450/3-77-033
11
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Foreword
Motor vehicle emissions control is becoming an increasingly large
part of each person's life who is associated with the automotive
industry. This is particularly true of the people that have to service
today's motor vehicles. Since the beginning of motor vehicle emissions
control in the mid-1960's, a number of different emissions control
systems have evolved. These systems have been augmented with a variety
of other devices that only add to the cluttered and confusing array of
wires, plumbing and vacuum hoses that are found under the hood of most
cars today. It is of little wonder that a large number of service
people feel intimidated and confused when they look under the hood of
today's cars.
It is the intent of this book and the student workbook to explain
each basic emissions control system and some of the more common devices
found on today's cars. Each discussion and exercise will be concerned
with the basic concept (what does the system do?) of a certain system.
If a service technician can understand the concept of a system and how
it relates to driveability and emissions, he is on the right road for
increasing profits, satisfying customers, and aiding in the effort
toward clean air.
Another advantage to learning the concepts of emissions control
systems is that, the same system concept applies to nearly every car.
This reduces some of the confusion that results from studying Ford's
system today, AM's system tomorrow and Chrysler's the day after. Once a
concept is understood that knowledge can be applied to nearly all cars.
r
The hardware may be somewhat different in appearance, but the job it is
performing is essentially the same.
We hope these booklets will help remove some confusion and aid the
mechanic in the performance of his job.
iii
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ACKNOWLEDGMENTS
The Motor Vehicle Emissions Control Staff of the Department
of Industrial Sciences at Colorado State University would
like to acknowledge the efforts extended by the Environmental
Protection Agency, Research Triangle Park, for their contribu-
tions to the development of this booklet.
A special thanks must be extended to the automotive vehicle
equipment and parts manufacturers for their cooperation and
assistance in the development of this training material.
iv
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Instructor's Guide Book
The Instructor's Book is designed to allow the instructor or
facilitator to lead a group of students through the key points of each
emissions control system.
Each basic emissions control system presented will have the follow-
ing information provided.
PART IDENTIFICATION
The basic parts of each emissions control system will be identified.
Physical identification of each part involved in a system is important.
The identification of parts related to a specific system allows a person
to look under the hood of a car and "see" systems, rather than a confus-
ing mass of hoses, switches, and other devices. A very brief descrip-
tion of what the part does is also provided.
SYSTEM OPERATION
In this section the individual parts of each system are explained.
The total system is studied from a functional viewpoint which tells what
it is supposed to do. The way the system operates is explained, showing
flow paths, and variations due to different modes of engine operation.
Understanding how a system operates makes troubleshooting and correcting
problems a much simpler task.
SYSTEM CONTROL
This section deals with the control of a system. Many emissions
control systems are controlled by various temperature devices and/or
sources of engine vacuum. This section will deal with how a particular
system is or may be controlled. Understanding of this portion also
enhances the troubleshooting ability of the service technician.
v
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SYSTEM EFFECTS ON HC-CO AND DRIVEABILITY
This section deals with the effect of the system on emissions and
driveability. It explains how and why the system affects emissions and
driveability. It is hoped this section will build an appreciation of
the need for proper operation and adjustment of any system that affects
the internal combustion engine.
WORKSHEETS
For each system a basic worksheet is included. The purpose of this
worksheet is to enforce the previously covered material. The use of
hands-on and the effects that establishing different system conditions
have on emissions are extremely important tools in the learning process.
Incorporated with the worksheets are quick operational checks that can
be made on each system.
VI
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CONTENTS
Unit 1 - Cause and Effect 1
Hydrocarbons 1
Carbon Monoxide 2
Oxides of Nitrogen 2
Unit 2 - Infrared Exhaust Gas Analyzer 5
Parts of Analyzer 5
Causes for various HC-CO Meter Readings 6
Worksheet 11
Unit 3 - Ignition and Carburetion 13
Idle Mixture Adjustments - CO Emissions 13
Idle Mixture Adjustments - HC Emissions 14
Advancing Ignition Timing - HC Emissions 14
Worksheet 16
Unit 4 - Positive Crankcase Ventilation 17
Crankcase 18
Ventilation 18
Closed PCV System 18
Flow of Blowby Gases 19
Purpose of PCV Valve 20
Control of HC, CO and Driveability 21
Operational Checks 23
Testing 25
Worksheet 25
Unit 5 - Thermostatic Air Cleaners 27
Types of TAG Systems 27
Parts Common to TAG Systems 28
Major Parts of Thermostatic Type 28
Major Parts of Vacuum Motor Type 29
Operating Modes Common to TAG Systems 29
Operation and Control of Thermostatic Type 31
Operation and Control of Vacuum Motor Type 32
Emissions and Driveability 35
vn
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Operational Checks 36
Worksheet . 39
Unit 6 - Air Injection Systems 41
Main Components 41
Air Flow 42
Diverter Valve Operation 43
Pressure Buildup Diverter Valve 44
Purpose of Air Switching Valve 44
Gulp Valve 45
Control of HC, CO and Driveability 46
Operational Checks 47
Worksheet 50
Unit 7 - Fuel Evaporation Control 51
Components of System 51
Operation of System 53
Methods to Purge Fuel Vapors 55
Operation of Carburetor Fuel Bowl Vents 57
Control of HC, CO and Driveability 57
Maintenance Checks 58
Worksheet 59
Unit 8 - Exhaust Gas Recirculation 61
Purpose of EGR Valve 61
Control Components 62
Ported Vacuum EGR with CTO Switch 63
Venturi Vacuum EGR with CTO Switch 64
Ported Vacuum EGR with Back Pressure Sensor 65
Control of HC, CO, NO and Driveability 66
a
Operational Checks 68
Worksheet 72
Unit 9 - Spark Control Systems 73
Purpose for Retarted Spark Timing at Idle 73
Parts of Transmissions Control Spark System ..... 73
Operation of Transmissions Controlled Spark
System 74
Vlll
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Transmission Controlled Spark System with
CTO Switch 75
Transmission Controlled Spark System with
Hot and Cold Temperature Switch 76
OSAC Valve 78
Control of HC, CO, NO and Driveability 79
J*±
Operational Checks 80
Worksheet 83
Unit 10 - Catalytic Converter Systems 85
Purpose of Catalytic Converter 85
Construction of Converter 86
Engine Performance Effects Catalytic Converter
Operation 86
Purpose of Protection Systems 87
Operation of Protection Systems 88'
Purpose of Exhaust System Heat Shield 90
Use of Unleaded Fuel 90
Control of HC, CO, NO and driveability 90
X
Worksheet 92
IX
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UNIT 1
CAUSE AND EFFECT
- BACKGROUND INFORMATION -
Throughout this course of study, the terms, Hydrocarbons (HC),
Carbon Monoxide (CO) and Oxides of Nitrogen will be used frequently -
These are terms that should be understood by today's service technician.
These terms appear in all information relating to emissions control.
They appear on the majority of VEHICLE EMISSIONS CONTROL INFORMATION
labels found under the hood of today's cars. A service technician must
understand these terms if he is to properly adjust today's automobiles,
and properly use today's test equipment. Knowledge of these terms also
aids the technician in giving explanations to customer-related questions.
A. Discuss Hydrocarbons.
Hydrocarbons, abbreviated HC, are the chemical components that make
up all petroleum products. This includes gasoline, fuel oil, and
lubricating oil. In regard to today's cars, hydrocarbon (HC)
emissions indicate gasoline that did not burn. This may be expressed
as unburned hydrocarbon emissions.
* ^ J^*\»»\"^
HYDROCARBONS
PPM.
This meter shows us how much
unburned gasoline (HC) is leaving
the engine and being exhausted to
the air.
Figure 1-1
-------
Hydrocarbon emissions contribute to the following conditions.
1. The formation of photochemical smog.
2. Eye irritation
3. Health hazards - some unburned hydrocarbons are suspected
of causing cancer and other health related problems.
B. Discuss Carbon Monoxide.
Carbon Monoxide (CO) results from incomplete combustion. In order to
burn a given amount of gasoline completely, a certain amount of air
must be present. If there is too much fuel present for the amount of
air, carbon monoxide (CO) emissions increase. As the proper amount
of air becomes available for a certain amount of fuel - CO emissions
decrease.
This meter shows us how closely the
carburetor is adjusted. Low CO -
close to proper air/fuel ratio.
High CO - rich mixture; too much
fuel, not enough air.
""'"^f
^^
CARBON MONOXIDE
PERCENT
Figure 1-2
Carbon Monoxide is a colorless, ODORLESS, DEADLY gas. CO emissions
can cause
1. Death - if inhaled in large enough quantities
2. Headaches and nausea in lesser amounts
3. Increased difficulty in breathing for people having respiratory
problems.
C. Discuss Oxides of Nitrogen.
Oxides of nitrogen (NO ) result from the combustion or burning
X
-------
process in the engine. Seventy-eight (78%) percent of the air we
breathe is made up of nitrogen. When this air is drawn into the
engine and burned at temperatures greater than approximately 2500°F,
NO or oxides of nitrogen are formed.
X
Instruments are available that read NOX emissions. Because
of their high cost, they are not usually found in automobile
service facilities.
Oxides of nitrogen (NO ) emissions contribute to the following condi-
X
tions.
1. NO + sunshine and hydrocarbons form photochemical smog.
J^
2. NO contributes to the dirty brown color associated with
photochemical smog.
3. Ozone (O~) results from chemical reactions involving NO .
j X
a) Ozone contributes to the smell associated with
photochemical smog.
b) Ozone also acts as an irritant to the eyes and
lungs.
c) Ozone causes rubber products to rapidly deteriorate
and is harmful to many types of plants.
-------
UNIT 2
INFRARED EXHAUST GAS ANALYZER
-BACKGROUND INFORMATION-
The infrared exhaust gas analyzer is a piece of test equipment used
to measure hydrocarbons' and carbon monoxide. The infrared unit provides
a hydrocarbon reading in parts per million (PPM). (One (1) part per
million is equivalent to 1 second in 11.5 days.) Carbon monoxide read-
ings are given in percent (%). Normally the hydrocarbon meter and the
carbon monoxide meter have two scales — a high scale and a low scale.
Either scale can be selected by pressing the appropriate button or
shifting a selector switch. The infrared analyzer can provide much
valuable information for diagnostic work. However, to utilize the in-
frared in this manner requires an understanding of hydrocarbons (HC) and
carbon monoxide (CO). Hydrocarbons are unburned fuel. There is always
a small portion of gasoline that does not burn. The hydrocarbon meter
shows how much unburned fuel is being exhausted. Carbon monoxide is a
product of incomplete burning. If too much fuel is present for the
amount of air present, the CO meter will show a large amount of carbon
monoxide being exhausted to atmosphere. Understanding HC and CO and
continued use of the infrared exhaust gas analyzer together with an
oscilloscope can greatly increase diagnostic capabilities.
A. Explain the basic parts of an infrared exhaust gas analyzer.
1. Infrared Heater - Provides a con-
stant source of infrared waves or
energy through the reference and
sample cells.
2. Chopper Wheel - A segmented disc
driven by a motor. The disc
-------
CHOPPER
SAMPLE
IN
SAMPLE
CELL
IR SOURCES
., SEALED
REFERENCE
CELL
constantly interrupts the infrared
signal. This provides a pulsating
infrared signal.
3. Sample Cell - A cell that the
exhaust gases flow through.
Infrared or energy is absorbed by
the HC and CO as they pass through
the sample cell.
4. Reference Cell - A cell that
contains no HC or CO. No infrared
waves or energy is absorbed in
this cell.
5. Detector - Changes the infrared
signals from the filters to an
electrical signal.
6. Amplifier - Increases the electri-
cal signal from the detector to
provide meter readings.
B. Explain some of the possible causes for the following HC-CO meter
readings.
NOTE: All readings must be taken with the engine at operating
temperature. ZERO and SPAN analyzer following manufacturer's
procedure.
SAMPLE _
OUT
DETECTOR —
U SIGNAL TO PREAMP
Figure 2-1
-------
» ^^V^ W» . i .....,....i ....i . 'f» 7O\ /.
\
HYDRpCARBONS
PPM.
CARBON! MONOXIDE
PERCENT
Figure 2-2
HYDROCARBO
PPM.
1. With the engine at operating temp-
erature and idling, Figure 2-1
shows a "normal" reading.
NOTE: "Normal" readings vary from
car to car. The normal
readings shown here do not
apply to catalytic converter
equipped cars.
Lo
Scale
Lo
Scale
CARBON IIONOXIDE
2. Symptoms - Rough idle. Possible
causes :
a) Ignition System Problem
1) Timing too far advanced
2) Fouled or shorted spark plug
3) Open or grounded spark plug
wire
4) Crossed spark plug wires
5) Leaking valves
6) Leaking EGR valve
7) Primary ignition system
problem
Hi
Scale
Figure 2-3
NOTES :
-------
3. Symptoms - Rough idle
HYDROCARBON
PPM.
Hi
Scale
a) Lean misfire
1) Idle mixture set too lean
2) Wrong PCV valve or PCV valve
stuck open
3) Vacuum line cracked or pulled
off
ON MONOXIDE
PERCENT
Lo
Scale
Figure 2-4
4 . Symptoms - Rough idle
a) Carburetion problem
1) Idle mixture set too rich
2) Improper choke operation or
setting
3) Leaking power valve
4) Float level too high
5) Restricted air cleaner
element
Lo
Scale
CARBON MONOXID
PERCENT
Hi
Scale
Figure 2-5
NOTES:
8
-------
HYDROCARBONS
PPM.
,v >> "» ""'""/'",/„ V\"
^ 1 J ''' '°'i.
v ' « , 'A/*//
I 4 5 ,j^-o>c. J-
"'"'»'*„,/,,^>T> ^
/jl/j/.
CARBON MONOXID
PERCENT
Figure 2-6
^
v'"
CARBONl M0NOXIDE
PERCENT
Figure 2-1
5. No rough idle
a) Air injection system not working
Hi
Scale
6. Symptoms - Engine surging, 1500 rpm
a) Erratic EGR valve operation
b) Timing too far advanced
Lo
Scale
NOTES:
-------
^\ ^V«*«*11* '"'''f't'^
v-^\ / '
HYDROCARBONS
PPM/
RBON', MONOXIDE
PERCENT
Figure 2-8
* <^ /\^""""""/'//,/;,,.,° ;»<^> /
/ ""^
CARBON MONOXIDE
Figure 2-9
7. Symptoms - Engine surging, 1500 rpm
a) Carburetion too lean
Lo
Scale
Lo
Scale
V**^*\
HYDROCARBON^
8. Symptoms - Possible black smoke,
2500 rpm
a) Carburetion problems
1) Main metering system too rich
2) High float level
3) Improper power valve
operation
4) Choke not fully open
Lo
Scale
Hi
Scale
10
-------
YbROiARBONS
\RPM.
9. Symptoms - Occasional miss, 1500-
2500 rpm.
a) Occasional ignition misfire
Lo b) Sticking valve (s)
Scale
CARBON\ MONOXIDE
PERCENT
LO
Scale
Figure 2-10
Have your students fill out the following worksheet in the student
workbook.
Engine Speed
0
0
Idle
Idle
Idle
Idle
Worksheet
Test Conditions
Warm up - Zero and Span
Analyzer
Remove gas cap. Hold probe
next to filler neck. Which
meter indicates unburned
gasoline?
Record HC and CO for
reference reading.
Remove and ground one spark
plug wire.
Remove air cleaner unit.
Partially close choke.
HC
(PPM)
—
CO
(%)
—
11
-------
1. Why did CO decrease when one spark plug wire was disconnected?
2. Why did HC increase when one spark plug wire was disconnected?
12
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UNIT 3
IGNITION AND CARBURETION
- BACKGROUND INFORMATION -
Adjusting basic ignition timing and carburetor idle mixture screws
has always been a part of a tuneup. Since the introduction of motor
vehicle emissions controls, these basic adjustments have become critical.
Timing and carburetor idle adjustment are a major part of effective
vehicle emissions control. It is interesting to note that approximately
80% of the cars that fail an idle emissions check can be corrected by
PROPERLY adjusting ignition timing and idle mixture. It is possible to
achieve an acceptable idle quality and decent performance and still keep
hydrocarbon and carbon monoxide levels low.
A. Explain how carburetor idle mixture adjustments affect CO emissions.
1. CO emissions are directly related
to the air/fuel ratio which at idle
is controlled by the idle mixture
adjustment screws.
a) Point A in Figure 3-1 shows a
recommended factory idle mixture
setting. This setting had CO
emissions of .3%.
b) Point B shows the increase in CO
emissions resulting from richen-
ing the idle mixture adjustment
screws 1/4 turn. This resulted
in CO emissions of 2%.
c) Point C shows the effect of
turning out the idle mixture
screws another 1/4 turn. CO
emissions jumped to 4.6%.
d) Another 1/4 turn rich is shown
at point D. This increased CO
emissions to 6.5%.
f
7.0-
6.0-
5.0-
CO 40'
% 3.0-
2.0-
1.0-
0.3
[ \
1 1
A B C D
\
FACTORY 1/4 TURN 1/2 TURN 3M TURN
SPECS RICH RICH RICH
V )
Figure 3-1
Idle mixture screws adjustments
13
-------
e) 1% CO equals 10,000 parts per
million of CO. Turning the idle
mixture adjusting screws out
only 3/4 of a turn from factory
specifications increased CO
emissions from 3,000 ppm to
65,000 ppm.
Emphasize the importance of setting
the idle mixture screws and idle
speed adjustments according to the
manufacturer's recommended pro-
cedure.
B. Explain how carburetor idle mixture screw adjustments affect HC
emissions.
1. The richer the idle adjustment, the
less air or oxygen there is for
combustion. Rich mixtures increase
HC
PPM
300-
?nn-
150-
100-
50-
,
FACTORY 1/4 TURN 1/2 TURN 3/4 TURN
SPECS RICH RICH RICH
Figure 3-2
Idle Mixture Screws Adjustment
the amount of unburned fuel HC as
well as CO
a) Point A in Figure 3-2 shows the
HC readings when the carburetor
is set according to factory
specifications. This setting
had HC emissions of 70 PPM.
b) Point B shows the increase in
HC emissions resulting from
richening the idle mixture
screws 1/4 turn. This resulted
in HC emissions of 135 PPM.
c) Point C shows the effect of
turning out the idle mixture
screws another 1/4 turn. HC
emissions reached 195 PPM.
d) Another 1/4 turn rich is indi-
cated at point D. This increased
HC emissions to 250 PPM.
C. Explain why advancing ignition timing increases HC emissions.
1. The more ignition timing is ad-
vanced, the cooler the cylinder
14
-------
300-
200-
HC ,50-
PPM
100-
50-
I 1
A B C D
FACTORY *5' TIMING HO" TIMING »IS* TIMING
SPECS ADVANCE ADVANCE ADVANCE
Figure 3-3
Ignition Timing
walls and exhaust system become.
Decreasing cylinder wall and ex-
haust temperatures does not allow
extra burning to occur in these
areas. The result is increased HC
emissions.
a) Point A in Figure 3-3 shows the
HC emissions when timing is set
to factory specs. HC emissions
were 60 PPM.
b) Point E shows the increase in HC
emissions from advancing timing
5° over factory specs. HC
emissions increased to 90 PPM
c) Point C shows the effect another
5° advance in timing for a total
of 10°. HC emissions increased
to 190 PPM.
d) Point D represents another 5°
advance in initial timing for a
total of 15°. This increased HC
emissions to 250 PPM.
Emphasize the importance of setting ignition timing to factory speci-
fications. Remember as timing is advanced, the engine speed in-
creases. This requires a smaller throttle plate opening. The
smaller throttle plate opening makes it difficult to achieve the
proper air/fuel ratio at idle.
NOTE: The readings shown in Figures 3-1, 3-2 and 3-3 are representa-
tive. Some vehicles show larger increases in emissions levels
while others show less of an increase.
Have your students fill out the following worksheet in the student
workbook as they perform the tests.
15
-------
Engine Speed
Idle (manufac-
turer's specs.)
Idle - maintain
manufacturer ' s
recommended
idle speed
Idle - maintain
manufacturer ' s
recommended
idle speed
Test Conditions
Carburetor set at
manufacturer's specs.
1/4 turn rich on idle mixture
adjustment screw (s)
1/4 turn rich on idle
adjustment screw (s)
1/4 turn rich on idle
adjustment screw (s)
1/4 turn rich on idle
adjustment screw (s)
Reset idle mixture adjustment
screws to manufacturer's
specs
Timing set at manufacturer ' s
specs
Advance timing 5°
Advance timing 5°
Advance timing 5°
Advance timing 5°
Reset timing to
manufacturer's specs
HC
(PPM)
CO
(%)
16
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UNIT 4
POSITIVE CRANKCASE VENTILATION (PCV)
- BACKGROUND INFORMATION -
Unburned hydrocarbons (HC) make up a large portion of the blowby
gases that enter the engine crankcase. These blowby gases are forced
past the piston rings on the compression and power stroke. As far back
as the 1920's, it was known that these gases, namely unburned hydrocar-
bons, water vapor and other products of combustion, were hazardous to an
engine's longevity. Blowby gases, if left in the crankcase, caused
rusting, corrosion, oil dilution and the formation of sludge. The road
draft tube was used for many years to ventilate the engine crankcase.
This method allowed the blowby gases, which contain unburned hydro-
carbons, to be discharged to the atmosphere. The positive crankcase
ventilating systems began appearing in the 1960's with the advent of
motor vehicle emissions control. The positive crankcase ventilating
system does not discharge blowby gases back to the atmosphere. With
this system blowby gases are drawn back into the engine and burned.
This allows ventilation of the crankcase and provides 100% control over
this source of unburned hydrocarbons.
17
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CLOSED SYSTEM
A. Explain what areas of the engine are part of the crankcase. This can
be defined as: any area inside the engine where oil is not under
pressure. This includes the following areas:
1. The area above the oil level in
the oil pan, i.e., crankshaft area
connecting rod area.
2. The area where the valve lifters
and push rods are located.
3. The area under the valve cover(s)
where the rocker arms and upper
part of the valve train are
Figure 4-1 located.
B. Explain what is meant by the term "Ventilation."
Ventilation as applied to the engine crankcase, means that the blowby
gases must be drawn out and fresh air drawn in. By constantly remov-
ing blowby gases, the following problems are kept to a minimum.
1. Rusting of internal engine parts - caused by water vapor.
2. Corrosion of internal engine parts - caused by acids that
form from different gases in the blowby g'as. .
3. Oil dilution - caused by unburned fuel or hydrocarbons -
causes excessive engine wear due to poor lubrication.
4. Formation of engine deposits - can cause very hard deposits
that stick piston rings, valves, hydraulic lifters. Sludge
is also formed and can block oil pump pickup screens and
prevent proper lubrication.
C. Explain the main components of the "Closed" PCV system.
The closed PCV system has been standard equipment on the majority of
cars built since 1968.
18
-------
TYPE IV SYSTEM
(CLOSED SYSTEM)
PCV VALVE
HOSE-
SEALED
OIL DIP
STICK
FRESH AIR
AIR INTAKE
HOSE
BLOW-BY GASES
Figure 4-2
1. Sealed Oil Filler Cap - to prevent
the escape of blowby gases to the
atmosphere during heavy accelera-
tion.
2. Air Intake Hose - allows fresh air
to enter the engine crankcase from
the air cleaner.
3. PCV Valve - meters the flow of
blowby gases from the crankcase
back to the intake manifold for
reburning.
4. Sealed Oil Dipstick - prevents the
escape of blowby gases to atmos-
phere and aids in sealing the
crankcase.
D. Explain the flow of blowby gases in the closed PCV system.
1. Blowby enters the crankcase by
escaping past the piston rings.
2. Intake manifold pressure is nor-
mally much less than the pressure
in the crankcase. This difference
in pressure causes the blowby
gases to be drawn into the intake
manifold.
3. The amount of blowby gas that is
drawn into the intake manifold is
controlled by the PCV valve.
4. Fresh air is drawn into the
TYPE IV SYSTEM
(CLOSED SYSTEM)
3.
PCV VALVE
HOSE
SEALED
OIL DIP
STICK
FRESH AIR
4.
HOSE
BLOW-BY GASES
Figure 4-3
19
-------
SEALED
OIL DIP
STICK
TYPE IV SYSTEM
(CLOSED SYSTEM)
BLOW-BY GASES
Figure 4-4
crankcase through the air cleaner
and intake hose.
5. This is normal operation of the
system. During conditions of
excessive blowby, such as full
throttle acceleration, the system
operates as follows.
a) During full throttle accelera-
tion, the PCV valve cannot
accomodate the extra amount of
blowby gases.
b) The majority of the blowby gas
is forced out of the engine
through the sealed oil filler
cap and air intake base into
the air cleaner. From inside
the air cleaner, the blowby
gases are drawn down through
the carburetor into the engine
to be burned.
E. Explain the purpose of the PCV valve.
The PCV valve provides a metered opening that varies in size to cor-
respond to varying engine operating conditions and varying amounts of
blowby gases.
PCV VALVE OPERATING POSITIONS
1. With the engine shut off or during
a backfire condition the PCV valve
plunger will be against its seat.
ENGNE OFF OR BACKFRE
VALVE BODY
SPRING
PLUNGER
OR VAIVE
(BACK POSITION)
Figure 4-5
20
-------
IDLING OR LOW SPEED
VALVE BODY
SPRING
*?
PLUNGER
OR VALVE
(FORWARD POSITION}
Figure 4-6
HIGHER SPEED
(MDDLE POSITION)
VALVE
SPRNG
PLUNGER
OR VALVE
Figure 4-7
2. During periods of engine idling or
low cruise the following condi-
tions are present.
a) Normally only a small amount of
blowby during these engine
conditions.
b) Intake manifold vacuum high.
c) Plunger is pulled against
spring tension, off its seat.
d) Blowby gases are metered
through grooves to the intake
manifold..
3. As engine speed and load increase,
the following engine conditions
are present:
a) Blowby increases as the engine
load increases.
b) Less manifold vacuum allows the
spring to push the plunger back
toward its seat.
c) In this position there is more
area for the larger amount of
blowby gases to pass through.
F- Explain how the PCV system can affect HC and CO emissions and drive-
ability.
Since the PCV system draws unburned hydrocarbons and air into the
intake manifold it does affect the air/fuel ratio. This in turn
affects the HC and CO emissions as well as vehicle driveability.
21
-------
BODY
VALVE STUCK OPEN
PLUNGER
TO
MANIFOLD
VACUUM
HOSE
EXCESSIVE AIR FLOW AT IDLE
Figure 4-8
SLUDGE 6
OIL DEPOSITS
A
VALVE STUCK CLOSED
\I
SPRING
PLUNGER
Figure 4-9
1. PCV valve stuck in the maximum
flow position
a) Leans out air/fuel ratio and CO
emissions decrease.
b) HC emissions may increase due
to excessively lean air/fuel
ratio causing a lean misfire.
c) Excessively lean air/fuel ratio
can cause a very rough idle.
d) Oil consumption may increase
due to increased air flow
through crankcase.
2. PCV valve stuck in the minimum
flow position
a) Prevents proper ventilation of
crankcase at higher speeds and
loads.
b) Can lead to increased sludge
formation and internal engine
corrosion.
c) Can lead to oil saturated air
cleaner element (excessive
blowby being forced through air
intake pipe into air cleaner).
An oil saturated air cleaner
element can raise CO emissions.
Stress at this point the necessity for the proper PCV valve for a
•articular engine. The wrong PCV valve can cause any of the above
iroblems.
i. At this time SJTRESJ3 the following items.
1. Always check the manufacturer's service manual for:
a) Specified mileage when suggested maintenance should be
accomplished.
b) Location of crankcase filters. There is normally a
filter in the air intake line that runs from the valve
cover to the air cleaner. This filter can be found in
any of the following locations.
1) in the air cleaner
22
-------
2) in the oil filler cap
3) in the air intake line
4) inside the valve cover below the air intake line
c) Some manufacturers specify different PCV valve part
numbers at a certain number of miles. Be sure to re-
place the PCV valve with the proper one.
d) The suggested method for testing the PCV system.
H. PCV System Operational Checks.
The operational checks suggested here will indicate whether or not
the crankcase is properly sealed and if the PCV system is working.
It is possible for these operational tests to be passed with a wrong
PCV valve. Therefore, insure the proper PCV valve is used in the
system.
WHEN THESE CHECKS ARE PERFORMED, INSURE AREA IS WELL VENTILATED.
1. VACUUM DRAW TEST
OIL FILLER
HOLE
PCV
Figure 4-10
a) Start engine and warm to oper-
ating temperature.
b) Remove oil filler cap and block
all other sources of air to the
crankcase.
c) Place a piece of paper over the
oil filler hole.
d) After a short period of time
the paper should be drawn down
tightly by the vacuum created
in the crankcase by the PCV
system.
23
-------
PCV
INCLINED RAMP
8 BALL TESTER
PLACE OVER
OIL INLET
Figure 4-11
2. CRANKCASE VACUUM DRAW TEST USING
THE INCLINED RAMP AND BALL TESTER.
a) Start engine and warm to
operating temperature.
b) Remove oil filler cap and block
all other sources of air to the
crankcase.
c) Place the tester over the oil
filler opening.
d) If crankcase vacuum is satis-
factory the ball will move to
the GREEN AREA.
e) If a pressure exists in the
crankcase the ball will move
into the RED AREA.
3. CRANKCASE VACUUM DRAW TEST USING
THE ADJUSTABLE PCV SYSTEM TESTER.
a) Start engine and warm to
operating temperature.
b) Check adjustable tester catalog
and set tester to the specified
setting for the car to be
checked.
c) Block all other sources of air
to the engine crankcase.
d) Connect the tester to the oil
filler opening.
e) Hold tester in the upright
(vertical) position.
f) If a green color shows in the
slot the system is satisfactory.
g) If a yellow color shows in the
slot it means the PCV system is
marginal.
h) If a red color shows in the
slot, this indicates a pressure
in the crankcase.
NOTE: This tester can also be used to check the PCV valve operation.
CORRECT
ADAPTER
BE SURE TESTER
IS VERTICAL
Figure 4-12
24
-------
I. Testing the PCV valve.
If any of the above checks did not show a vacuum in the crankcase,
the PCV valve should be checked for proper operation.
1. CHECKING THE PCV VALVE.
a) Remove the PCV and shake it.
If a rattle is heard, this only
^ tells you the plunger is free.
It is no indication of the
physical condition of the
plunger.
PCV VALVE CHECK
b) Start the engine.
c) Place your finger over the end
of the PCV valve. You should
feel a strong vacuum.
d) If no vacuum is felt, remove
the PCV valve from the hose or
intake manifold connection.
e) Check for vacuum at the end of
the hose or manifold connection.
f) If no vacuum is felt, the hose
or intake manifold passages are
plugged and must be opened.
Have the students fill out the following worksheet in their student's
workbook as they perform the tests.
Figure 4-13
Engine Speed
IDLE
IDLE
IDLE
IDLE ,
Test Condition
VACUUM DRAW TEST
Place sheet of paper over
oil filler hole
VACUUM DRAW TEST
Inclined Ramp and Ball
VACUUM DRAW TEST
Adjustable Tester
PCV VALVE TEST
Pass
Fail
25
-------
UNIT 5
THERMOSTATIC AIR CLEANERS
- BACKGROUND INFORMATION -
Thermostatic air cleaners or heated air induction systems began
appearing on automobiles in 1967. This system became necessary as car-
buretor air/fuel ratios became leaner. Leaner carburetor air/fuel
ratios present a driveability problem when the engine is cold. Thermo-
static air cleaners provide heated air to the carburetor. Heated air
allows better fuel vaporization and more even fuel distribution; both of
these factors provide better driveability and reduce HC and CO emissions.
Thermostatic air cleaners are necessary with the shorter choke operation
time used on newer vehicles. The use of preheated air also minimizes
the problem of carburetor icing.
A. Explain that two different types of thermostatic air cleaner systems
are used. Although two types are used both are sensitive to air
temperature. The two types are:
THERMOSTATIC TYPE
1. Thermostatic type
Figure 5-1
27
-------
VACUUM MOTOR TYPE
VACUUM MOTOR
VACUUM HOSE
\
COLD AIR
TEMP SENSOR
TO EXHAUST
MANIFOLD-
SHROUD
HOT
AIR
AIR
CLEANER
2. Vacuum motor type
DAMPER ASSEMBLY
Figure 5-2
B. Explain the parts that are common to both types of thermostatic air
cleaner systems.
1. Exhaust manifold heat shroud - A
piece of formed metal around the
exhaust manifold that directs air
flow over the exhaust manifold to
preheat it.
2. Hot air pipe - directs the air from
the heat shroud to the air cleaner
snorkel.
3. Damper assembly - regulates when
and how much heated air enters the
air cleaner.
HOT AIR
PIPE
AIR HEATED BY MANIFOLD
TAG REDUCES HC 8 CO
Figure 5-3
C. Identify the major parts of the thermostatic type air cleaner.
1. Thermostat - senses the temperature
of the air entering the air cleaner
and expands or contracts depending
on temperatures.
28
-------
THERMOSTATIC TYPE
2. Damper Assembly - regulated by the
thermostat and spring to determine
when and how much heated air enters
the air cleaner.
3. Spring - aids the thermostat in the
control of the damper assembly.
VACUUM MOTOR
VACUUM HOSE
TEMP SENSOR
VACUUM MOTOR
Figure 5-4
D. Identify the major parts of the vacuum motor type air cleaner.
1. Vacuum motor - controlled by intake
manifold vacuum to open or close
the damper assembly.
2. Temperature sensor - senses the
incoming air temperature and con-
trols the amount of vacuum applied
to vacuum motor.
3. Vacuum hose - connects vacuum motor
to temperature sensor and a source
of manifold vacuum.
DAMPER ASSEMBLY
TO EXHAUST
MANIFOLD
SHROUD
Figure 5-5
E. Explain the three operating modes that are common to both types of
air cleaner.
These three modes are common to both types of air cleaners.
29
-------
HOT AIR MODE
AIR FILTER
TO EXHAUST
MANIFOLD SHROUD
Figure 5-6
REGULATING MODE
Figure 5-7
1. Hot air mode - when under-hood
temperatures are below approxi-
mately 90°F, the damper assembly
blocks cold air. Only heated air
is allowed to enter the air cleaner
2. Regulating mode - In this mode the
damper assembly allows both heated
air and cold air to mix. The air
temperature entering the air
cleaner is regulated at approxi-
mately 100-130°F.
3. Cold air mode - When temperatures
inside the air cleaner exceed 120-
130°F, the damper assembly blocks
off the heated air and allows only
cold air to enter the air cleaner.
Figure 5-8
30
-------
F. Explain the operation and control of the thermostatic type air
cleaner.
1. Below approximately 100°F the ther-
INCOMING AIR BELOW SPECIFIED
TEMPERATURE (APPROX. 100°)
Figure 5-9
Figure 5-10
REGULATING MODE
mostat is in a retracted position.
a) This position plus the pull of
the spring forces the damper
assembly into the position
shown.
b) In this position cold air is
prevented from entering the
carburetor.
c) As soon as the engine is started,
the exhaust manifold begins to
warm up. Air drawn over the
exhaust manifold on the way to
the carburetor is heated.
2. As the heated air temperature rises
to approximately 105°F, the thermo-
stat begins to expand.
a) As the thermostat expands, it
pulls against the spring and the
damper assembly begins to move
down.
b) This allows some cold air to mix
with the heated air.
3. When the temperature of the thermo-
stat reaches approximately 130°F,
the thermostat has expanded enough
to overcome spring tension.
a) Heated air is completely closed
off to the air cleaner.
b) In this position only cooler
under-hood air is entering the
carburetor.
Figure 5-11
31
-------
HEAT DOOR IN PARTIAL HEAT-OFF
POSfTION UNDER COLD ACCELERATION
HOT AIR
VACUUM OVERRIDE
MOTOR jo MANIFOLD
VACUUM
Figure 5-12
4. Some thermostatic air cleaners are
equipped with a vacuum override
motor.
a) At engine idle or low speed
cruising conditions, manifold
vacuum aids in keeping the
damper assembly in the hot air
mode.
b) Upon accelerating manifold
vacuum drops. This drop in
manifold vacuum allows the
spring in the override motor to
override the thermostat and
spring.
c) The damper assembly moves to the
regulated or cold air mode.
This provides denser air for
more power during acceleration.
G. Explain the operation and control of the vacuum motor type air
cleaner.
VACUUM MOTOR TYPE AIR CLEANER
DIAPHRAGM SPRING
VACUUM MOTOR,
DIAPHRAGM \
DAMPER
ASSEMBLY
TO EXHAUST
MANIFOLD -
. SHROUD
1. With the engine shut off, the
damper assembly should be in the
cold air mode. The damper assembly
is held in this position by the
spring in the vacuum motor.
Figure 5-13
32
-------
AIR BLEED
VALVE
CLOSED
TEMPERATURE
SENSING
SPRING
FULL
VACUUM
SIGNAL TO
VACUUM MOTOR
TO MANIFOLD
VACUUM
Figure 5-14
HOT AIR DELIVERY MODE
DIAPHRAGM SPRING
VACUUM MOTOR
DIAPHRAGM \
Figure 5-15
AIR BLEED
OPEN
TEMPERATURE
SENSOR
SPRING
LOW
OR NO
VACUUM
SIGNAL
TO
VACUUM
MOTOR
TO MANIFOLD
VACUUM
2. When the temperature of temperature
sensor is below approximately 85°F,
the small air bleed valve is held
closed by a temperature-sensitive
spring.
3. When the engine is started, full
manifold vacuum reaches the vacuum
motor.
a) Vacuum overcomes the spring
tension and the damper assembly
moves to the hot air delivery
mode.
b) Air being drawn into the carbu-
retor is preheated by being
pulled over the exhaust manifold.
4. As the heated air begins to warm,
the temperature-sensitive spring in
the temperature sensor, the air
bleed valve begins to open. This
small air leak destroys some of the
vacuum to the vacuum motor. This
occurs between 85° to approximately
105°F.
Figure 5-16
33
-------
REGULATING MODE
DIAPHRAGM SPRING
VACUUM MOTOR
DIAPHRAGM \
Figure 5-17
AIR BLEED
OPEN
LOW
OR NO
VACUUM
SIGNAL
TO
VACUUM
MOTOR
TEMPERATURE
SENSOR
SPRING
TO MANIFOLD
VACUUM
Figure 5-18
VACUUM MOTOR
DIAPHRAGM \
COLD AIR DELIVERY MODE
DIAPHRAGM SPRING
5. As the vacuum decreases to the
vacuum motor the spring forces the
damper assembly downward into the
REGULATING MODE. In this position
colder under-hood air is mixed with
heated air.
6. When the temperature in the air
cleaner reaches approximately 130°F,
the air bleed valve allows more air
to enter the vacuum line. This
reduces the vacuum to the vacuum
motor.
7. When the vacuum to the vacuum motor
drops to approximately 3-8" Hg, the
damper assembly is forced down into
the COLD AIR DELIVERY MODE. Only
cold air enters the air cleaner.
Figure 5-19
34
-------
LOW VACUUM CONDITION
VACUUM MOTOR
\ DIAPHRAGM SPRING
DIAPHRAGM \
8. During cold engine acceleration,
manifold vacuum drops.
a) Less vacuum at the vacuum motor
allows the spring to force the
damper assembly downward.
b) Cool, dense air is allowed to
enter the carburetor for better
performance.
Figure 5-20
H. Explain how heated air systems affect EC/CO emissions and vehicle
driveability.
Carburetor idle and off-idle circuits have become progressively
leaner since 1968. This, coupled with shorter choke operating times,
presents a definite driveability problem.
1. Heated air to the carburetor allows
better fuel vaporization. This in
turn:
a) Gives better fuel distribution.
b) Increases driveability when cold.
HOT AIR DELIVERY MODE
DIAPHRAGM SPRING
VACUUM MOTOR
DIAPHRAGM \
Figure 5-21
c) Decreases HC and CO emissions by
allowing a leaner air/fuel ratio.
2. Some vacuum motor systems use a
small vacuum delay valve in the
vacuum motor vacuum line. This
prevents:
a) The damper assembly from rapidly
going to the COLD AIR MODE on
acceleration.
b) Lessens hesitation and stumble
on acceleration.
35
-------
TO MANIFOLD VACUUM /
v. L
OPENING
TO
EXHAUST
HEAT
SHROUD
HOT IDLE
COMPENSATOR
SENSOR
Figure 5-22
3. Some vacuum motor systems have a
"hot idle compensator" connected to
them.
a) Between 120-140°F percolation of
fuel can cause excessive rich-
ness and rough idle.
b) Compensator opens between 120-
140°F to allow "extra" air to
enter intake manifold.
c) "Extra" air leans out the exces-
sive richness.
d) Improves engine idle quality and
reduces HC-CO emissions.
I. Thermostatic Air Cleaner Operational Checks
Explain that the operational checks suggested here are for proper
operation of the system. They are visual checks only. Consult a
manufacturer's service manual for exact temperature and vacuum
specifications. WHEN THESE CHECKS ARE PERFORMED - INSURE AREA IS
WELL VENTILATED.
1. THERMOSTATIC AIR CLEANER OPERA-
TIONAL TEST.
, v a) Thermostat should be below
approximately 85°F.
b) Check damper assembly position -
it should be blocking COLD AIR,
i.e., HOT AIR DELIVERY MODE.
c) Check air pipe for tight
connections, tears.
d) Start engine.
e) After a few minutes, tough the
hot air pipe. It should be
warming up.
f) Watch the damper assembly in the
air cleaner. It should begin to
move out of the hot air delivery
mode.
THERMOSTATIC AIR CLEANER
Figure 5-23
36
-------
NOTE:
g) If equipped with vacuum override
motor, accelerate engine rapidly
and return to idle - damper
assembly should move down during
acceleration, allowing cold air
to enter.
h) As the thermostat in the air
cleaner becomes warm, the damper
assembly should move downward
until the heated air inlet is
completely blocked, allowing
only air to enter.
If the thermostatic air cleaner does not operate as described,
inspect the spring and damper assembly for binding. Correct
as necessary. If no binding is present, the thermostat or
temperature sensitive pellet will have to be replaced. CHECK
THE MANUFACTURER'S SERVICE MANUAL FOR EXACT PROCEDURES.
k 2. VACUUM MOTOR OPERATED OPERATIONAL
TEST.
VACUUM MOTOR AIR CLEANER
VACUUM MOTOR
Figure 5-24
a) Temperature sensor should be
below approximately 80°F.
b) With the engine shut off, check
the damper assembly position.
It should be open to cold air.
c) Check air pipe for tight
connections at manifold heat
shroud and bottom of air
cleaner snorkel.
d) Start engine, the damper
assembly should move to the hot
air mode.
NOTE:
If the damper assembly does not move to the hot air mode,
check the following:
1) Disconnect the vacuum line to
the vacuum motor.
2) Connect a vacuum gauge to the
vacuum line. It should read
full intake manifold vacuum
(approximately 16-20" Hg.).
37
-------
3) If full manifold vacuum is
available, check damper
assembly for binding. If no
binding exists, a new vacuum
motor is needed. (Vacuum
motor can also be checked
using a hand vacuum pump.)
4) If a very low vacuum (3-8"
Hg.) is shown, the tempera-
ture sensor must be replaced.
e) As the engine and air cleaner
assembly warm up, the damper
assembly should go into the
regulating mode and then the
cold air mode.
NOTE: If the damper assembly does not follow this sequence, the
temperature sensor must be replaced. CHECK THE MANUFACTURER'S
SERVICE MANUAL FOR EXACT PROCEDURES.
Have your students fill out the following worksheet in the Student Work-
book as they perform the tests.
NOTE: Exact temperatures can be checked by placing a small thermo-
meter inside the air cleaner.
38
-------
THERMOSTATIC AIR CLEANER WORKSHEET
Engine
Speed
Test
Conditions
Cold Air
Mode
Regulating
Mode
Hot Air
Delivery Mode
THERMOSTATIC TYPE
Off
Idling
Temperature
Below 80°F
Temperature
Between
100-130°F
If equipped with vacuum
override motor
Snap Accel-
eration
Idling
Temperature
Between
100-130°F
Temperature
Above 130 °F
VACUUM MOTOR TYPE
Off
Idling
Idling
Idling
Check
Position
Temperature
Below 80°F
Temperature
Between
100-120°F
Temperature
Above 130°F
39
-------
UNIT 6
AIR INJECTION SYSTEMS
- BACKGROUND INFORMATION -
Approximately 60% of the hydrocarbons and carbon monoxide that make
up automobile emissions are discharged out of the tailpipe. These
emissions result from incomplete combustion or burning in the engine.
One very important element necessary for combustion to occur is oxygen.
Since the air we breathe is made up of approximately 20% oxygen, air can
be injected very close to the outlet side of the exhaust valve. When
air is injected in this location, it allows the burning of the air/fuel
mixture to continue in the exhaust system of the car thereby reducing
the amount of HC and CO exhausted to the atmosphere.
The air injection system has been used by the car makers off and on
since 1967. It is a very effective method for reducing the HC and CO
emissions from the internal combustion engine.
The air injection system has many different names. Each manufac-
turer has their own special name for it. All of these systems are very
similar and perform the same job. Don't let the names confuse you.
A. Explain the main components of the Air Injection System.
1. Air Pump - A belt driven pump that
supplies air to the air injection
system.
2. Diverter Valve - Prevents air from
entering the exhaust system during
deceleration. This prevents back-
firing. It also acts as a pressure
relief valve.
MANIFOLD VACUUM
SIGNAL LINE
PUMP
DIVERTER
VALVE
MANIFOLD
Figure 6-1
41
-------
3. Check Valve - Allows air flow into
the exhaust manifold and prevents
the exhaust gases from entering the
air injection systems.
4. Air Distribution Manifold - Directs
the air to the vicinity of each
cylinder's exhaust valve.
5. Manifold Vacuum Signal Line - Pro-
vides manifold vacuum signal to
diverter valve.
B. Explain the air flow through the system during normal engine opera-
tion.
1. Air is drawn into the pump through
a centrifugal filter. The centri-
fugal filter is a small, plastic,
round filter behind the belt
pulley. This filter has vaned
openings to prevent the entrance of
foreign particles into the pump.
2. Air from the pump is forced into a
diverter valve. During normal idle
or cruise conditions the diverter
valve allows air flow to pass on to
the check valve.
3. Air is allowed to pass through the
check valve in one direction only,
that direction being towards the
air distribution manifold.
Figure 6-2
42
-------
4. Air enters the distribution mani-
fold and is evenly distributed to
the exhaust part of each cylinder.
5. As the air comes in contact with
the hot exhaust gases, the exhaust
gases continue to burn. This
reduces the amount of HC and CO
that is exhausted out of the
tailpipe.
C. Explain the operation of the diverter valve during normal operation.
, N 1. During idle and cruise conditions,
air flow through the diverter valve
is as shown. Air enters the
diverter valve, flows around the
stem and open upper valve and is
directed out to the air distribu-
tion manifold.
VENT
Figure 6-3
HIGH
INTAKE
MANIFOLD
VACUUM
SIGNAL
AIR
FLOW
SEATED
Figure 6-4
2. During deceleration:
a) A manifold vacuum sensing line
senses the sharp increase in in-
take manifold vacuum when the
throttle closes.
b) The increase in intake manifold
vacuum pulls down a diaphragm.
c) When this diaphragm is pulled
down, the air is prevented from
passing to the check valves and
air distribution manifold.
d) The air is directed downward,
through silencing material and
out to the atmosphere.
43
-------
e) This "dump" condition lasts 2-4
seconds. A small orifice allows
vacuums to equalize on both
sides of the diaphragm. When
vacuums equalize, normal air
flow is restored.
D. Explain the operation of the diverter valve when excessive pressure
builds up in the diverter valve.
^__ v 1. The diverter valve acts as a relief
valve when air pressure becomes
excessive.
5PSI
VENT
5PSI
AIR
FLOW
Figure 6-5
a) Pressure works against the lower
valve.
b) This causes the stem to move
downward.
c) In this position some air is
"dumped" to atmosphere. Most of
the air continues to flow
towards the exhaust manifold.
E. Explain the purpose of the air switching valve. Air switching valves
are found on some catalytic converter equipped vechicles. They are
included here so students can become aware of them.
a) The source of vacuum to the air
switching valve is controlled by
a temperature sensitive switch.
b) At low temperatures, vacuum is
applied to the valve and all the
air is directed to the exhaust
ports.
c) Above a certain coolant tempera-
ture vacuum is prevented from
reaching the valve.
d) The valve now directs the
majority of the air to exhaust
header pipe.
e) A small amount of air is still
directed to the exhaust ports.
INTAKE
MANIFOLD
VACUUM
AIR SWITCHING VALVE
Figure 6-6
44
-------
CHECK VALVE
F. Explain the operation of the air injection system check valve.
1. The check valve has a spring
loaded steel diaphragm.
2. Air can flow from the pump to the
exhaust manifold.
Figure 6-7
3. In case of pump belt breakage, hose
rupture, or excessive exhaust back
pressure, the steel diaphragm
prevents exhaust gas from reaching
air system components.
Figure 6-8
G. Explain the operation of the "Gulp" valve.
Gulp valves are used on some vehicles instead of a diverter valve.
__ _^ 1. The gulp valve is used to prevent
backfire during deceleration.
2. The gulp valve is operated by the
sharp increase in manifold vacuum
that accompanies deceleration.
3. This increase in vacuum causes the
gulp valve to vent a portion of
pump air into the intake manifold.
Figure 6-9 ,c
SIGNAL LINE
TO
INTAKE
MANIFOLD.
AIR DISCHARGE
TO
GULP VALVE INTAKE MANIFOLD,
-------
4. This air "leans out" the rich mix-
ture that accompanies deceleration
and prevents a backfire from
occuring.
5. A relief valve is usually located
on the air pump if the system uses
a gulp valve.
H. Explain how the air injection system can affect HC and CO emissions
and driveability.
1. Disconnecting the air injection
system can cause emissions to be
two to three times higher than with
the system operating.
2. Some injected air is drawn into the
combustion chamber during idle.
a) Improper diverter valve opera-
tion, pump failure, or blocked
check valve can cause a rough
idle condition if air flow is
blocked.
3. Improper diverter valve operation
can cause backfires to occur.
4. Air pumps require very little
power; disconnecting them will not
show any appreciable increase in
fuel economy or power.
NOTE: On 1975 and newer vehicles with catalytic converters, some air
injection systems may be controlled differently than described
above. Check the manufacturer's service manual for differ-
ences BEFORE conducting any OPERATIONAL CHECKS.
46
-------
I. Air Injection System Operational Checks.
The following suggested operational checks will show whether or not
the system is operating. It is strongly suggested that the proper
manufacturer's service manual is referred to for additional checks
and specific procedures.
WHEN PERFORMING ANY CHECKS THAT REQUIRE THE ENGINE TO BE RUNNING,
INSURE WORK AREA IS WELL VENTILATED.
1. AIR PUMP DRIVE BELT
a) Check belt for wear and proper
tension (manufacturer's service
manual). Loose belts slip,
glaze, squeal and prevent proper
pump operation. Belts that are
too tight can cause early bush-
ing and/or bearing failures.
Figure 6-10
AIR INLET
FILTER
2. CENTRIFUGAL FILTER
A) Visually inspect for excessive
wear or breakage.
Figure 6-11
47
-------
MANIFOLD VACUUM
SIGNAL LINE
PUMP
VISUALLY INSPECT
ALL HOSES
3. VISUAL INSPECTION OF ALL HOSES -
AIR AND VACUUM
a) Visually inspect all hoses for
1) Loose connections
2) Worn spots
3) Excessive brittleness
4) Sharp bends that pinch off
air flow or vacuum
Correct as necessary.
Figure 6-12
Figure 6-13
Figure 6-14
4. AIR PUMP FLOW TEST
a) Remove pump discharge hose at
the check valve.
b) Start engine.
c) Check air flow at hose outlet.
d) Increase speed to approximately
1500 rpm.
e) Air flow should increase as
engine speed increases.
f) If air flow does not increase
perform diverter valve checks
before condemning pump.
5. DIVERTER VALVE TEST (1974 vehciles
and older)
a) Locate vent hole(s) on diverter
valve.
b) At idle no air should be flowing
out of vent holes. If air is
being dumped at idle, a new
diverter valve is needed. (This
could cause the iar pump flow
not to increase in air pump
test.)
c) Increase engine speed to approx-
imately 2000 rpm.
A a
-------
CAUTION:
CHECK VALVE
AND
EXHAUST GASES
ARE HOT!
d) Let throttle close rapidly. Air
should be dumped for 1-3 seconds
during this time.
e) If vacuum is present, diverter
valve should be replaced. Not
dumping can cause backfiring.
If diverter does not dump on
deceleration, remove vacuum
sensing hose and check for
vacuum. A strong vacuum should
be felt anytime the engine is
running.
6. CHECK VALVE TEST
a) Remove hose from check valve(s).
b) Start engine.
Figure 6-15
c) Hold your hand over the check
valve opening. If no exhaust is
felt, check valve is O.K. Use a
pencil or other narrow object to
push down on check valve dia-
phragm. Diaphragm should move
freely; if not, replace check
valve. If exhaust pulsations
are felt, check valve is
acceptable. If a solid flow of
exhaust gas if felt, check valve
should be replaced.
Figure 6-16
49
-------
AIR TO
INTAKE MANIFOLD
AIR FROM PUMP
7- GULP VALVE TEST
a) Pinch hose closed between gulp
valve and intake manifold.
Engine speed should not change.
If it does, this means the gulp
valve is leaking and should be
replaced.
b) Remove the manifold vacuum
sensing line for approximately
five seconds. Then reconnect
line. If engine idle changes
when line is reconnected gulp
valve is operating properly.
Figure 6-17
Have your students fill out the following worksheet as they perform the
tests.
AIR INJECTION SYSTEM WORKSHEET
Engine Speed
0
0
0
Idle and
1500 rpm
Idle
2000 rpm
Idle
Idle
Test Condition
AIR PUMP DRIVE BELT
CENTRIFUGAL FILTER
AIR AND VACUUM HOSE CONDITION
PUMP AIR FLOW AT DISCHARGE HOSE
END
DIVERTER VALVE TEST
DIVERTER VALVE DISCHARGE ON
DECELERATION
GULP VALVE TEST
GULP VALVE TEST
Pass
Fail
50
-------
UNIT 7
FUEL EVAPORATION CONTROL
- BACKGROUND INFORMATION -
Up to this point the control of hydrocarbon emissions by the PCV
system, Thermostatic Air Cleaner and Air Injection System have been dis-
cussed. All of these relate directly to the combustion process within
the engine. However, when gasoline evaporates, unburned hydrocarbons
enter the atmosphere. It has been estimated that approximately 20% of
the total hydrocarbon emissions result from the evaporation of gasoline
in the carburetor and fuel tank. Consequently, all cars sold in the
United States since 1971 were required to have some type of fuel
evaporative control system for these evaporative HC emissions.
Earlier, pre-emissions fuel tanks drew air in through the fuel
filler cap as gasoline was used. When the fuel expanded in the tank,
gasoline vapors were simply pushed back out of the fuel filler cap to
atmosphere. Gasoline vapors from earlier carburetor fuel bowls were
allowed to escape to atmosphere as well. The Fuel Evaporation Control
system (FEC) now controls this source of hydrocarbon emissions.
A. Explain the main components of the Fuel Evaporation Control system.
Figure 6-7 shows a typical fuel evaporation control system. Exact
components may vary in physical description but the concept is the
same for all systems.
1. Fuel Tank - Fuel tanks have been
redesigned to provide approximately
10% air space for the expansion of
fuel as temperatures increase.
51
-------
VAPOR SAVER SYSTEM
PURGE
LINE
FUEL TANK
VENT LINE
PRESSURE
VACUUM
SAFETY
FILLER CAP
CHARCOAL
CANISTER
OVERFILL
LIMITING
VALVE
LIQUID
VAPOR
SEPARATOR
2. Fuel Tank Filler Caps - Prevent the
escape of gasoline vapors to atmo-
sphere under normal operating
conditions.
3. Liquid-Vapor Separator - Separates
liquid fuel from the vapors. The
liquid fuel is returned to the fuel
tank.
4. Fuel Tank Vent Line - Routes the
vapors from the liquid vapor
separator forward to the overfill
limiting valve.
5. Overfill Limiting Valve - Prevents
any liquid fuel that enters the
vent line from reaching the char-
coal canister. (This part is not
found in all systems.)
6. Charcoal Canister - Stores the fuel
vapors in activated charcoal.
7. Purge Line - Provides a means for
drawing fresh air through the can-
ister to remove or purge fuel
vapors out of the activated char-
coal and delivering these vapors to
the engine to be burned.
Note: In 1976 a design requirement for all cars was to pass a 360°
roll over test without losing any liquid fuel. Many of the
devices that prevent loss of fuel are a part of newer fuel
Figure 7-1
52
-------
evaporation control systems. Consult the manufacturer's
service manual for specific information on these parts.
This is necessary for proper repair and to maintain fuel
system integrity in the event of vehicle rollover.
B. Explain the operation of the Fuel Evaporation Control system.
1. Fuel tank filler necks have been
changed to prevent the tank from
being completely filled. The
lower position of the filler necks
allow approximately 10% air
expansion space above the fuel
level.
AIR SPACE PROVIDED FOR
FUEL EXPANSION
10-12% OF TANK VOLUME
FILLER
NECK
FUEL
TANK
FUEL
Figure 7-2
PRESSURE-VACUUM RELIEF CAP
TANK PRESSURE l/g - I PSI
SEALING
GASKET
OUTER SHELL
PRESSURE
SPRING
PRESSURE'
RELIEF
VALVE (OPEN)
VACUUM RELIEF
LOCKING
LIP
VALVE (CLOSED) VACUUM SPRING
Figure 7-3
2. When the filler cap is reinstalled,
fuel vapors are trapped in the tank.
Fuel tank caps incorporate a built-
in pressure relief valve and a
vacuum relief valve. The pressure
relief valve will vent excessive
pressure to atmosphere - only if
there is a blockage in the vent line
to the canister.
53
-------
CAP RELIEVING TANK VACUUM
VACUUM 1/4"- 1/2" HG
SEALING
GASKET
PRESSURE
SPRING
OUTER SHELL
PRESSURE
RELIEF
VALVE
(CLOSED)
VACUUM RELIEF
VALVE (OPEN)
LOCKING
LIP
VACUUM
SPRING
Figure 7-4
HORIZONTAL MOUNTED LIQUID
VAPOR SEPARATOR
-TO CHARCOAL
MOUNTING
Figure 7-5
BUILT-IN SEPARATOR
RESTRICTOR
ORIFICE
FOAM
-FUEL TANK
Figure 7-6
3. The cap will also allow air to
enter the fuel tank if an excessive
vacuum (approximately 1/2"-1"-Kg)
develops in the tank.
NOTE: The normal vent path for
air to enter the fuel tank is from
the charcoal canister back through
the vent line to the fuel tank.
4. Vapors in the fuel tank flow out of
the tank into a liquid vapor sepa-
rator. This can be a horizontal
separator as shown in Figure 6-5.
Vent lines enter this separator
from different areas of the tank.
Any liquid fuel that enters the
separator is returned to the fuel
tank through the liquid return line.
Gasoline vapors leave the separator
through the vent line on the top of
the separator.
5. Some vapor separators are installed
in the top of the fuel tank as
shown in Figure 6-6. An open cell
foam allows vapors to pass through
but restricts the flow of liquid
fuel.
NOTE: There are many types of
Liquid Vapor Separators. Consult
54
-------
CHARCOAL CANISTER
HOSE TO'
CARBURETOR
OR
AIR CLEANER
CHARCOAL
GRANULES
OUTSIDE AIR
HOSE TO
FUEL TANK
VENT
CANSTER
CASE
FBERGLAS
FILTER
the manufacturer's service manual
for the vehicle you are working on.
6. Fuel vapors pass forward to the
charcoal canister. Activated
charcoal in the canister adsorbs
the vapors. These stored vapors
are prevented from escaping to
atmosphere. When the engine is
started these vapors are drawn into
the engine and burned.
Figure 7-7
C. Explain the different methods used to purge fuel vapors from the
charcoal canister.
1. Variable Purge - This method uti-
lizes the air flow into the air
cleaner to purge the charcoal
t I \
AIR
CLEANER
TANK
-CARBON
CANISTER
Figure 7-8
canister.
a) A tube in the air cleaner snor-
kel senses differences in air
flow.
b) As engine speed is increased,
more air flows by the tube.
c) The low pressure created in the
tube draws air into the bottom
of the charcoal canister.
d) The air passes over the charcoal
and lifts off the gasoline
vapors.
e) The air and vapors are drawn
into the air cleaner and burned
in the engine.
55
-------
The variable purge depends on engine speed. The higher the engine
speed, the greater the air flow and the greater the purge rate on
the canister.
2. Demand Purge - This method utilizes
the throttle plates in the carbure-
tor as control valve for purging.
PORTED
VACUUM
RESTRICTED
ORIFICE
CARBURETOR
BOWL VENT
DEMAND
PURGE SYSTEM
FROM
FUEL
TANK
a) The canister purge line is
connected to a port above the
throttle plates in the carbu-
retor.
b) As the throttle is opened, the
purge ports are uncovered.
c) A low pressure is created in the
purge line to the canister.
d) The low pressure created causes
air to be drawn through the
charcoal canister towards the
carburetor.
e) The fuel vapors drawn from the
canister with the air are pulled
into the engine and burned.
The demand purge only purges when the throttle is opened. This pre-
vents extra fuel vapors from entering the carburetor during idle.
3. Constant and Demand Purge - This
system utilizes the PCV system and
throttle plate position for control.
Figure 7-9
RESTRICTED
ORIFICES
CARBURETOR
BOWL VENT
CONSTANT 8 DEMAND
Figure 7-10
a) One connection from the canister
is tied into the line with the
PCV valve. This is the constant
purge portion.
b) A small restriction in the can-
ister limits the purge rate
during idle. The small amount
that is purged is drawn in with
blowby gases and burned in the
engine.
c) When the throttle is opened, A
vacuum signal opens the purge
valve on the canister. This
56
-------
CARBURETOR
TO CANISTER
/ TO CARB.
LINKAGE
allows a higher canister purge
rate at increased engine speed.
D. Explain the operation of carburetor fuel bowl vents.
The carburetor was another source of hydrocarbon emissions. This is
especially true when the engine is idling or shut off. Carburetors
are now vented internally or to the canister to limit evaporative
emissions.
1. When the throttle is in the idle
position, a small valve is mechani-
cally opened. This small valve
allows fuel vapors to pass from the
carburetor float bowl to the char-
coal canister. Venting is allowed
anytime the throttle is at idle
position, regardless if the
engine's running or stopped.
2. As the throttle is opened, the fuel
bowl vent valve closes. Venting
does not occur when the throttle is
opened.
THROTTLE
CLOSED
Figure 7-11
TO CANISTER
TO CARBURETOR
LINKAGE
CLOSED ANTI
PERC VftLVE
CARBURETOR
BOWL
THROTTLE
OPEN
Figure 7-12
E. Explain how the FEC system can affect EC/CO emissions and drive-
ability.
57
-------
1. Loose hose connections can allow
fuel vapors to enger the atmosphere
(HC emissions).
2. Torn seals on fuel tank filler caps
can allow fuel vapors to enter the
atmosphere (HC emissions).
3. During carburetor idle adjustment,
follow instructions on Vehicle
Emissions Control Information
Label. On some vehicles, purge
lines must be disconnected before
idle adjustments are made. If
adjustments are made with the
vehicle purge line connected the
idle mixture will lean out when the
canister is thoroughly purged.
This can cause a rough idle and
increased HC emissions because of
lean misfires.
Except as noted, the FEC system has little effect on driveability.
If a tight system is maintained, evaporative fuel losses will be
minimal. The vapors will be stored and burned in the engine at the
proper time.
F. Fuel Evaporation Control Maintenance Checks.
a) Check the condition of the
fiberglass filter on the bottom
58
-------
BOTTOM OF CANISTER
FIBERGLAS
FILTER
of the charcoal canister.
Replace as directed by the
OWNER'S MAINTENANCE SCHEDULE
BOOK.
b) Check all hose connections for
tightness.
c) Check seal on fuel tank filler
cap. If torn or cracked,
replace cap. Insure proper
replacement cap is installed.
Figure 7-13
NOTE: If any hoses in the FEC system must be replaced, use only the
proper fuel resistant hose.
Have the students fill out the following worksheet in the student's
workbook as they perform the tests.
Engine Speed
0
0
0
0
0
0
Test Condition
VISUAL INSPECTION
Fuel tank filler cap
Fuel tank and hose connection
condition
Liquid vapor separator and/or
check valve condition
Type of purge system
Canister line condition
Filter condition
Pass
Fail
59
-------
UNIT 8
EXHAUST GAS RECIRCULATION
- BACKGROUND INFORMATION -
One pollutant from motor vehicles not yet discussed is N0x- NOx or
oxides of nitrogen result from the high temperatures of the combustion
process. When air and fuel are burned in the internal combustion engine,
temperatures up to 4500°F can be reached. NO is formed very rapidly
X
above approximately 2500°F. In 1973 federal standards were established
to limit the amount of NOX resulting from the combustion process in the
internal combustion engine. The auto manufacturers chose the exhaust
gas recirculation system (EGR) as the primary means of controlling NOx
emissions. The EGR system allows a small amount of burned exhaust gas
to be mixed, in the intake manifold, with the incoming air/fuel mixture.
The inert exhaust gas dilutes the air/fuel mixture. Dilution results in
lower combustion chamber temperatures and controls NO emissions.
X
A. Explain the purpose of the EGR valve.
1. The EGR valve controls the amount
of exhaust gas recirculated back to
intake manifold.
2. Directly below the EGR valve is an
opening to the exhaust system. As
the EGR valve opens, exhaust gas
passes into the intake manifold to
dilute the air/fuel mixture.
3. The EGR valve is opened by a vacuum
signal. This vacuum signal must be
carefully controlled to insure
exhaust gas recirculation occurs at
61
CARBURETOR
AIR 8 FUEL
TO VACUUM SOURCE
EGR VALVE.
FROM EXH. SYSTEM UTO INTAKE MANIFOLD -
Figure 8-1
-------
the proper time in engine operation.
B. Identify and explain the components that can be used to control the
operation of the EGR valve.
1. Coolant temperature override switch
(CTO)
COOLANT
TEMPERATURE
OVERRIDE
\ SWITCH
Figure 8-2
EXHAUST BACK-PRESSURE
SENSOR (TRANSDUCER)
Figure 8-3
a) normally located in intake mani-
fold coolant passages.
b) temperature sensitive switch
c) normally senses engine coolant
temperature
d) placed in the vacuum line be-
tween the source of vacuum and
the EGR valve.
e) at low coolant temperature - no
vacuum is allowed to EGR valve
f) at preset temperature switch
opens and allows vacuum to reach
the EGR valve.
2. Exhaust Back Pressure Sensor
(Transducer)
a) senses exhaust system back
pressure
b) senses exhaust back pressure
from an exhaust port located in
a spacer under the EGR valve.
c) placed in the vacuum line be-
tween the source of vacuum and
the EGR valve.
d) at low exhaust back pressure no
vacuum reaches the EGR valve -
no exhaust gas recirculation
occurs.
e) at higher exhaust back pressure
vacuum is allowed to reach the
EGR valve and exhaust gas recir-
culation occurs.
62
-------
t TO INTAKE MANIFpjjj>
\ TO EGR VALVE^S-
C 'FROM VENTURI VAOJUM SIGNAL^
// ^
VACUUM AMPLIFIER
Figure 8-4
3. Vacuum Amplifier
a) senses carburetor venturi vacuum
b) uses the small carburetor ven-
turi vacuum signal to control
intake manifold vacuum
c) regulated intake manifold vacuum
is then used to control the EGR
valve
d) venturi vacuum signal is propor-
tional to air flow through the
carburetor
e) as engine speed and air flow in-
crease exhaust gas recirculation
occurs
C. Explain the operation of the Ported Vacuum EGR system with a CTO
switch.
1. Low Engine Coolant Temperature
Condition.
EGR
CTO
SWITCH
PORTED VACUUM SYSTEM
LOW COOLANT TEMPERATURE
CARBURETOR
EGR VALVE
Figure 8-5
a) As the throttle is opened, a
port is uncovered that allows
vacuum to the CTO switch.
b) Below a specified coolant tempr-
erature the CTO switch prevents
vacuum from reaching the EGR
valve.
c) If no vacuum reaches the EGR
valve no exhaust gas recircu-
lation can occur.
d) This improves the driveability
of a cold engine.
63
-------
PORTED VACUUM SYSTEM
COOLANT AT
NORMAL OPERATING TEMPERATURE
CARBURETOR
2. Normal Engine Coolant Temperature
Condition.
a) As the throttle is opened, a
port is uncovered that allows
vacuum to the CTO switch.
b) At normal operating temperature
the CTO switch will allow vacuum
to reach the EGR valve.
c) Exhaust gas recirculation will
occur under these conditions.
Figure 8-6
NO exhaust gas recirculation occurs at full throttle. Intake mani-
fold vacuum drops to value that is too small to hold open the EGR
valve.
NOTE: Explain to students at this time the necessity for checking
the manufacturer's service manual for CTO switch operating
temperatures. A large number of CTO switches with different
temperature settings are used. Check the Service Manual.
D. Explain the operation of the Venturi Vacuum EGR system with a CTO
switch.
1. Low Engine Coolant Temperature
. Condition
VENTURI VACUUM EGR SYSTEM
INTAKE MANIFOLD
VACUUM LINE
EGR VALVE
Figure 8-7
64
a) As the throttle is opened and
engine speed increases, a
venturi vacuum signal is
generated by the increased air
flow.
b) The venturi vacuum signal is
measured in the vacuum amplifier
and a proportional amount of
intake manifold vacuum is
allowed to pass through the
amplifier to the CTO switch.
c) Below a specified coolant temp-
erature, the CTO switch prevents
vacuum from reaching the EGR
valve.
-------
VENTURI VACUUM EGR SYSTEM
CARBURETOR
/
u_^_VENTURI VACUUM LINEs,
\
EGR VALVE
INTAKE MANIFOLD
VACUUM LINE
Figure 8-8
d) No exhaust gas recirculation is
allowed and cold engine drive-
ability is thereby improved.
2. Normal Engine Coolant Temperature
Condition
a) As the throttle is opened and
engine speed increases, a
venturi vacuum signal is gener-
ated by the increased air flow.
b) The venturi vacuum signal is
measured in the vacuum amplifier
and a proportional amount of
intake manifold vacuum is
allowed.
c) At normal operating temperatures
vacuum is allowed through the
CTO switch to the EGR valve.
d) Exhaust gas recirculation will
occur under these conditions.
E. Explain the Operation of the Ported Vacuum EGR system with the Back
Pressure Sensor.
NOTE: This system also uses a CTO switch. The function is the same,
vacuum is denied at low coolant temperature and allowed above
a specified temperature. Explain to the student the following
descriptions at normal operating temperature.
_ ^ 1. Engine running at idle or very low
speeds.
ENGINE IDLING
BACK PRESSURE
SENSOR FILTER
EXHAUST BACK,
PRESSURE W PORTED VACUUM
SENSING TUBE
L EXHAUST BACK PRESSURE
2. SENSOR AIR BLEED OPEN
'(AIR DRAWN REDUCES VACUUM)
3. NO PORTED VACUUM SIGNAL
«. EOR VALVE CLOSED
Figure 8-9
a) Exhaust back pressure is very
low.
b) Low back pressure allows spring
to push down diaphragm in sensor.
c) Air is allowed to be drawn into
sensor and vacuum lines destroy-
ing any vacuum taht is present.
d) No vacuum gets to the EGR valve
and no exhaust gas recirculation
occurs.
65
-------
ACCELERATION
TO INTAKE
MANIFOLD
I. EXHAUST BACK PRESSURE
HIGH
2 SENSOR AIR BLEED CLOSED
3 HIGH PORTED VACUUM SIGNAL
4. EGR VALVE OPEN
Figure 8-10
FULL THROTTLE OPERATION
I. EXHAUST BACK PRESSURE HIGH
2. SENSOR AIR BLEED CLOSED
3. LOW PORTED VACUUM SIGNAL
4. EGR VALVE CLOSED
2. Acceleration
a) Exhaust back pressure increases
during acceleration.
b) Increased back pressure forces
back pressure sensor diaphragm
up and seals off the air bleed
port.
c) Ported vacuum passes through the
CTO switch and back pressure
sensor to the EGR valve.
d) Exhaust gas recirculation will
occur under these conditions.
3. Wide Open Throttle Operation
a) Exhaust back pressure is very
high during acceleration.
b) High back pressure forces the
sensor diaphragm up closing off
the air bleed port.
c) During full throttle operation
ported vacuum is too low to
operate EGR valve.
d) The EGR valve remains closed
under these conditions and no
exhaust gas recirculation occurs.
Figure 8-11
NOTE: The EGR systems just covered are basic systems. Many manu-
facturers have added additional equipment to EGR systems not
shown here. If these systems are understood,, additional means
of control should be comprehensible to the students. Again,
encourage the use of the manufacturer's service manual or a
good emissions control service manual when working on any
system.
F. Explain how the EGR system affects HC-CO-NO emissions and drive-
^t
ability.
66
-------
NO is not normally measured at an automotive service facility. NO
X X
analyzers are very expensive and not normally found in reapir stations.
NOV is controlled within federal limits if the EGR system is operating
X
as it was designed to operate. Failure of EGR system components can
cause hydrocarbon readings to be high at idle. Failures can also
cause low speed driveability problems.
1. EGR valve that does not close
EGR VALVE
NOT
PROPERLY
CLOSED
Figure 8-12
properly
a) exhaust gas allowed into the
intake manifold at idle
b) HC emissions may increase due to
misfiring of cylinders caused by
excessive dilution at idle
c) excessive dilution at idle can
cause a rough idle condition due
to misfiring
d) can cause rough off-idle accel-
eration problems due to exhaust
dilution.
2. Conditions that can cause the EGR
valve to open too soon or not close
completely
a) malfunction EGR system vacuum
amplifier
b) malfunctioning back pressure
sensor with the wrong part
number
c) improper idle speed adjustment
that allows EGR vacuum port to
be uncovered at idle
d) EGR valve replacement that is a
wrong part number
e) carbon buildup on valve or valve
seat
67
-------
Figure 8-13
3. Leaking EGR valve to base gasket
This allows exhaust gases to pass
into intake manifold without going
through the valve.
4. CTO switch failure
a) If vacuum is allowed when the
engine is cold a cold drive-
ability problem will result.
This will disappear as the
engine warms up.
b) If vacuum is never allowed NOX
emissions will be high, possible
problem with detonation, i.e.,
tip in ping - or ping during
high speed acceleration.
Stress the necessity for proper
part number replacement. Improper
part replacement can cause drive-
ability problems as well as exces-
sive emissions. Stress the use of
VACUUM CIRCUIT DIAGRAMS and visual
inspection of all vacuum bases for
kinks, cracks, splits, looseness
and excessive hardness.
G. EGR System Operational Checks
Note: Insure area is well ventilated before performing these checks.
1. EGR Valve Operational Check
a) Start engine and allow it to
come to operating temperature.
b) Disconnect the vacuum line at
the EGR valve.
c) Connect a hand pump to the EGR
valve and apply 8-16" of vacuum.
68
-------
EGR
VALVE
Figure 8-14
PORTED VACUUM SYSTEM
LOW COOLANT TEMPERATURE
EGR
CTO
SWITCH
CARBURETOR
EGR VALVE
Figure 8-15
VENTURI VACUUM EGR SYSTEM
INTAKE MANIFOLD
VACUUM LINE
EGR VALVE
d) The engine should begin to idle
roughly and possibly stall. The
engine should smooth out when
vacuum is removed from the EGR
valve.
e) If the EGR valve does not open
when vacuum is applied to it,
replace the EGR valve.
NOTE: Most manufacturers recom-
mend removing and inspect-
ing the EGR valve at the
following intervals.
1) every 12,000 miles if
leaded gasoline is used.
2) every 25,000 miles if
unleaded gasoline is
used.
If this maintenance is not per-
formed carbon and/or lead
deposits build up around the
valve seat and valve. These
deposits could prevent the valve
from closing completely or keep
it from opening.
2. Ported vacuum and venturi vacuum
EGR system with CTO switch.
Operational check - engine cold.
a) Start engine, coolant tempera-
ture should be below 80°F.
b) Increase engine speed to approx-
imately 2000 rpm while watching
the stem on the EGR valve.
c) The stem should not move while
the engine is cold.
d) If the stem on the EGR valve
does move with the engine cold,
the CTO switch is defective.
Figure 8-16
69
-------
NOTE: If EGR valve stem is not visible, tee a vacuum gauge into the
vacuum line to the EGR valve. Check for vacuum signal rather
than stem movement. This applies to all EGR system checks.
N 3. Ported vacuum and venturi vacuum
EGR system with CTO switch opera-
PORTED VACUUM SYSTEM
COOLANT AT
NORMAL OPERATING TEMPERATURE
EGR
CTO
SWITCH
CARBURETOR
EGR VALVE
Figure 8-17
VENTURI VACUUM. EGR SYSTEM
CARBURETOR
VENTURI VACUUM LINE\
VACUUM
AMPLIFIER
INTAKE MANIFOLD
VACUUM LINE
EGR VALVE
tional check - engine warm.
a) Start the engine, coolant
temperature should be above
160°F.
b) Increase engine speed to
approximately 2000 rpm while
watching the stem on the EGR
valve or the vacuum gauge.
c) The stem should move with the
engine at operating temperature
or a vacuum reading will be
seen.
Figure 8-18
NOTE: These procedures are basic. Consult the manufacturer's service
manual for exact procedures for testing and troubleshooting.
4. Ported vacuum EGR system with
exhaust back pressure sensor opera-
tional check.
a) Start the engine, coolant
temperature should be below 80°F.
b) Increase engine speed to
approximately 2000 rpm and ob-
serve the. vacuum gauge or the
EGR valve stem.
70
-------
ENGINE IDLING
BACK PRESSURE
SENSOR
EXHAUST BACK
PRESSURE
SENSING TUB
L EXHAUST BACK PRESSURE
2. SENSOR AIR BLEED OPEN
(AIR DRAWN REDUCES VACUUM)
3. NO PORTED VACUUM SIGNAL
4. EGR VALVE CLOSED
Figure 8-19
c) The valve stem should not move
and/or the vacuum gauge should
read 0" Hg.
NOTE: It may be necessary to parti-
ally restrict exhaust flow to
insure back pressure sensor
receives an adequate pressure
signal.
d) Let the engine warm up to opera-
ting temperature.
e) Increase speed to 2000 rpm and
observe EGR valve stem or vacuum
gauge. At operating temperature
the EGR valve should begin to
open.
f) It may be necessary to partially
restrict exhaust flow to insure
the back pressure sensor re-
ceives an adequate pressure
signal.
NOTE: Cars with single exhaust sys-
tems use a different back
pressure than cars with a
dual exhaust system. Be sure
the one you are going to
install is the proper sensor.
If a dual exhaust sensor is
used on a car with a single
exhaust system this will
cause a driveability problem.
A dual exhaust sensor operates
at a lower back pressure. If
this sensor is used on a vehicle
with a single exhaust system it
will result in too much exhaust
gas recirculation. This will
cause a large drop in engine
power and fuel economy.
Have the students fill out the following worksheet in the student's work-
book as they perform the tests.
71
-------
Engine
Speed
Idle
2000
rpm
2000
rpm
2000
rpm
2000
rpm
Test
Conditions
EGR VALVE OPERATIONAL CHECK
Ported Vacuum or Venturi Vacuum
EGR Systems
Engine Cold
Check EGR valve stem movement or
vacuum to EGR valve
Engine Warm
Check EGR valve stem movement or
vacuum to EGR valve
Ported Vacuum EGR System with Back
Pressure Sensor
Engine Cold
Check for valve stem movement or
vacuum to EGR valve
Engine Warm
Check EGR valve stem movement or
vacuum to EGR valve
Pass
Fail
Vacuum
Reading
72
-------
UNIT 9
SPARK CONTROL SYSTEMS
- BACKGROUND INFORMATION -
Spark control systems, or the control of ignition, timing, have been
around since the late 1960's. The purpose of spark control systems is
to control the advance or retard of ignition timing. Controlling timing
in this manner improves combustion and reduces the amount of N0x and
hydrocarbons emissions from the engine.
The majority of spark controls control the vacuum to the vacuum
advance unit. This is the primary means of spark control today.
A. Explain the purpose for retarded spark timing at idle.
1. Retarding timing at idle causes
a) Engine speed to slow down.
LARGER
THROTTLE
OPENING
HOTTER EXHAUST
TEMPERATURE
Figure 9-1
b) Throttle plates must be opened
further to bring engine rpm up
to manufacturer's specifications.
c) Larger throttle opening allows
more air to enter the engine,
i.e., leaner air/fuel ratio.
This reduces HC emissions.
d) Since ignition is taking place
closer to TOP dead center, the
temperature of the exhaust
leaving the engine is hotter.
e) Hotter exhaust temperatures plus
the leaner air/fuel ratio allows
some burning to occur in the ex-
haust system. This also reduces
HC emissions.
B. Identify the parts of a typical Transmission Control Spark System.
1. Carburetor - Provides a timed
source of vacuum for the vacuum
advance unit. (Vacuum port
73
-------
SOLENOID VACUUM
SWITCH
DISTRIBUTOR
VACUUM
ADVANCE UNIT
CARBURETOR
TRANSMISSION
SWITCH
normally located above throttle
plates. No vacuum signal until
throttle is opened.)
2. Vacuum Advance Unit - Advances
ignition timing for maximum economy
during cruising conditions. This
is accomplished by a vacuum signal.
3. Solenoid Vacuum Switch - Prevents
or allows vacuum to reach the
vacuum advance unit.
4. Transmission Switch - Controls the
solenoid vacuum switch. This is
accomplished by amking or breaking
the circuit between the ignition
switch and solenoid vacuum switch.
C. Explain the operation of the transmission controlled spark system.
1. Transmission in lower gears
IGNITION
Figure 9-2
SOLENOID VACUUM
SWITCH
DISTRIBUTOR
CARBURETOR
TRANSMISSION
SWITCH
VACUUM
ADVANCE UNIT
IGNITION
Figure 9-3
a) When the transmission (manual or
automatic) is in any lower gear
the transmission switch is
closed.
NOTE: This is the case for MOST
cars. Emphasize the neces-
sity for checking the manu-
facturer's service manual for
exact specifications and
settings.
b) With the transmission switch
closed, the circuit is completed
and the solenoid vacuum switch
is energized.
c) When the solenoid vacuum switch
is energized vacuum is prevented
from reaching the vacuum advance
unit.
d) Vacuum advance is denied.
74
-------
SOLENOID VACUUM
SWITCH
DISTRIBUTOR
VACUUM
ADVANCE UNIT
/
IGNITION
2. Transmission in high gear.
a) When the transmission is in high
gear, the transmission switch
opens.
b) When the transmission switch
opens, the circuit to the sole-
noid vacuum switch is broken.
c) With the circuit broken, the
solenoid vacuum switch is de-
energized and vacuum is allowed
to reach the vacuum advance unit.
d) The vacuum advance unit now
allows normal vacuum advance to
occur.
Figure 9-4
NOTE: Solenoid vacuum switches may be activated by governor oil
pressure. If this arrangement is used, the system operates
according to vehicle speed rather than gear selection. One
manufacturer used a small generator in the speedometer cable.
The generator put out a voltage proportional to vehicle speed.
The generator signal ctonrolled the solenoid vacuum switch.
Emphasize the necessity for checking the manufacturer's service
manual or a good emissions control manual BEFORE working on
these systems.
D. Explain the operation of a transmission controlled spark system with
a coolant temperature (CTO) override switch.
Vacuum advance is allowed at low coolant temperatures on some
vehicles. Allowing vacuum advance improves cold driveability.
1. When coolant temperature is below
approximately 160°F
a) The CTO switch allows manifold
vacuum (below the throttle
plates) to pass directly to the
vacuum advance unit.
75
-------
TO IGNITION
SWITCH
OPEN OVER
35MPH
OR HIGH GEARS
Figure 9-5
TO IGNITION
SWITCH
OPEN OVER
35MPH
OR HIGH GEARS
Figure 9-6
b) The solenoid vacuum switch is
bypassed.
c) Full vacuum advance is allowed
anytime the coolant temperature
is below 160°F.
d) Ported vacuum is blocked below
160°F by the CTO switch and the
solenoid vacuum switch when the
transmission is in the lower
gears.
2. When coolant temperature is above
approximately 160°F
a) The CTO switch blocks manifold
vacuum to the vacuum advance
unit.
b) Ported vacuum is allowed to pass
through the CTO switch anytime
the vehicle is in high gear.
c) In high gear the solenoid vacuum
valve is de-energized and allows
vacuum to pass to the vacuum
advance unit.
E. Explain the operation of a transmission controlled spark system with
hot and cold coolant temperature override switches.
NOTE: The solenoid vacuum valve is omitted from the firts two
figures for simplicity.
1. Coolant temperature above approxi-
mately 160°F.
a) Ported vacuum from the carbure-
tor first goes to the hot over-
ride switch.
76
-------
BELOW 225T-ABOVE I60°F
HOT OVERRIDE
PORTED
VACUUM
-CTO
PORTED
VACUUM
b) If coolant temperature is below
approximately 225°F, ported
vacuum passes through the hot
override switch to the CTO
switch.
c) Above 160°F coolant temperature
ported vacuum is allowed to the
vacuum advance unit.
Figure 9-7
ABOVE 225°F
PORTED
VACUUM
-CTO
HOT OVERRIDE
MANIFOLD
VACUUM
Figure 9-8
2. Coolant temperature above approxi-
mately 225°F
a) Above 225°F the hot override
switch blocks ported vacuum.
b) Manifold vacuum is allowed to
pass through the hot override
switch to the CTO switch.
c) Manifold vacuum passes through
the CTO switch to the vacuum
advance unit.
d) The added spark advance in-
creases engine speed, which
increases fan speed and coolant
flow to lower coolant tempera-
ture.
e) Figure 9-9 shows the ssysem with
the solenoid vacuum valve in
place.
1) The solenoid vacuum valve
allows or denies ported
vacuum depending on which
gear the transmission is in.
2) During a hot override condi-
tion, manifold vacuum by-
passes the solenoid vacuum
valve.
77
-------
PORTED
VACUUM
TO
DISTRIBUTOR
Figure 9-9
F. Explain the operation of the spark delay valve.
1. The spark delay valve delays the
vacuum to the vacuum advance unit.
2. As the throttle is opened vacuum
reaches the black side of the spark
delay valve.
3. Vacuum is delayed between 5-20
seconds depending on the color of
the side the spark delay valve
facing the vacuum advance unit.
4. When the throttle is closed, vacuum
is immediately removed from the
vacuum advance unit.
G. Explain the operation of the OSAC valve.
1. OSAC (Orifice Spark Advance Control)
valves delay the vacuum to the
vacuum advance unit.
2. As the throttle is opened vacuum
reaches the lower side of the OSAC
valve.
3. A delay of approximately 26 seconds
is built into the OSAC valve. It
takes this long for vacuum to
equalize on both sides of the OSAC
valve.
4. When the throttle is closed, vacuum
is removed immediately from the
vacuum advance unit.
TO
DISTRIBUTOR
PORTED
VACUUM
OSAC
VALVE
Figure 9-10
78
-------
5. Some OSAC valves permit vacuum to
reach the vacuum advance unit
immediately below 60°F. Above 60°F
it takes approximately 26 seconds.
H. Explain how spark control systems can affect HC, CO and NO emissions
j"t
and driveability.
1. Over advancing initial spark timing
raises HC, CO and NO emissions.
X
a) If timing is over advanced the
throttle plates must be closed
down to maintain special idle
speed.
b) This makes it very difficult to
obtain low HC and CO levels and
an acceptable idle.
c) Advanced timing increases NOX
emissions because of higher peak
flame temperatures during com-
bustion.
2. Failure of transmission controlled
spark system.
a) If vacuum is allowed in the
lower gears, excessive HC and
NOX emissions will result.
There will be little appreciable
gain in performance and fuel
economy -
b) If vacuum never reaches the
vacuum advance unit, poor fuel
economy will result.
3. Failure of CTO or hot override
switch.
a) If failure allows full manifold
vacuum at all times high idle HC
emissions levels will result.
b) If failure allows only ported
vacuum at all times, poor cold
engine driveability will result.
79
-------
4. Improper Spark Delay valve or OSAC
valve operation.
a) If vacuum is not delayed, higher
levels of HC and NOX emissions
will results.
b) If vacuum is completely blocked
by these components, poor fuel
economy will result.
Note: There are many variations in spark control systems. The con-
cepts covered in this unit should allow other spark control
systems and devices to be readily understood.
I. Spark Control Systems Operational Checks.
The operational checks suggested here will show whether or not the
system or device is operating. It is strongly suggested that the
proper manufacturer's service manual or a good emissions control
manual be referred to for additional checks and specific procedures.
1. Transmission Controlled Spark
system (Automatic Transmission).
a) Tee a vacuum gauge into the
vacuum advance line between the
distributor and the solenoid
• vacuum switch.
b) Start the engine and bring to
operating temperature.
c) Apply foot brake.
d) Shift transmission selector to
reverse.
e) Increase engine speed to approx-
imately 1500 rpm and observe
vacuum gauge.
f) A vacuum reading indicates the
system is operational.
Figure 9-11
80
-------
0 VACUUM
~j2ND GEAR
1ST GEAR
PORTED VACUUM
3RD GEAR
Figure 9-12
Figure 9-13
2. Transmission Controlled Spark
(standard Transmission).
a) Tee a vacuum gauge into the
vacuum advance line between the
distributor and the solenoid
vacuum switch.
b) Start the engine and bring to
operating temperature.
c) Depress the clutch, increase
engine speed to approximately
1500 rpm and move the gear shift
through the lower gears. No
vacuum reading should occur.
d) When the gear shift lever is put
into high gear, a vacuum reading
will indicate the system is
operational.
3. Speed Controlled Spark System
a) Tee a vacuum gauge into the
vacuum line between the distribu-
tor and the solenoid vacuum
switch.
b) Raise both rear wheels and set
jack stands.
c) Start engine and warm to opera-
ting temperature.
d) Shift transmission selector into
DRIVE.
e) Observe the vacuum gauge and
slowly increase speed.
f) A vacuum reading between 25-35
mph indicates the system is
operational.
81
-------
TESTING SPARK DELAY VALVE
Figure 9-14
TESTING SPARK DELAY VALVE
4. Spark Delay valve Operational Test
a) Remove spark delay valve.
b) Connect a hand vacuum pump to
the BLACK side of the valve.
c) Pump up approximately 12-14" Hg,
of vacuum.
d) The gauge should slowly drop to
0" Hg.
e) Replace the valve if the gauge
does not drop to zero.
a) Connect a hand vacuum pump to
the colored side of the valve.
b) Attempt to pump up a vacuum.
c) If a vacuum can be established,
replace the valve.
Figure 9-15
NOTE: Spark delay valves can be tested on the vehicle. Tee a vacuum
gauge in between the spark delay valve and distributor.
Increase speed to approximately 1500-2000 rpm. Vacuum should
slowly increase and drop to zero when the throttle is closed.
5. OSAC Valve Operational Test.
Figure 9-16
a) Tee a vacuum gauge into the
vacuum line between the OSAC
valve and distributor.
b) Start engine and bring to oper-
ating temperature.
c) Increase engine speed to
approximately 1500-2000 rpm.
d) If vacuum builds up to maximum
in 15-25 seconds, and drops to
zero when the throttle is closed
OSAC valve is operational.
82
-------
e) If no vacuum reading or a very
low vacuum reading is present
after 30 seconds, replace the
valve.
Have the students fill out the following worksheet in the student's
workbook as they perform the tests.
Engine
Speed
Test Conditions
TRANSMISSION CONTROLLED SPARK (AUTOMATIC)
Approxi-
mately
1500 rpm
Engine at operating temperature
Transmission selector in reverse
TRANSMISSION CONTROLLED SPARK (STANDARD)
Approxi-
mately
1500 rpm
Engine at operating temperature
1st gear (clutch depressed)
2nd gear (clutch depressed)
3rd or high gear (clutch depressed)
SPEED CONTROLLED SPARK SYSTEM
Slowly
increase
to 40
mph
Engine at operating temperature
Rear wheels raised/jack stands
Increase speed to approximately
40 mph
SPARK DELAY VALVE
Approxi-
mately
1500-
2000 rpm
or use
hand
pump
OSAC VALVE
150.0-
2000 rpm
Throttle
Closed
Engine at operating temperature
Pass
Fail
Vacuum
Reading
83
-------
UNIT 10
CATALYTIC CONVERTER SYSTEMS
- BACKGROUND INFORMATION -
The catalytic converter appeared on a majority of 1975 automobiles.
The federal standards for HC and CO emissions that had to be met for
1975 and newer cars required the use of a very effective emissions con-
trol device. The catalytic converter's effectiveness in reducing HC and
CO emissions prompted its introduction to meet these stricter standards.
The catalytic converter is placed in the exhaust system fairly
close to the engine. The converter treats exhaust gases after they
leave the engine. By treating the exhaust after it leaves the engine,
the engine could be retuned for better performance and economy. The
catalytic converter does not adversely affect the performance of the
engine. However, the performance and tuning of the engine does affect
the operation of the catalytic converter.
A. Explain the purpose of the catalytic converter.
1. The catalytic converter performs
the following functions.
SECONDARY COMBUSTION OR
BURNING OCCURS IN THE
CATALYTIC CONVERTER
Figure 10-1
a) Provides a place where secondary
burning of the exhaust gases can
take place.
b) Secondary burning allows for a
more complete oxidation or burn-
ing of the exhaust gas.
c) A complete oxidation or burning
process results in large amounts
of HC and CO being converted
into water vapor (H2O) and car-
bon dioxide (CO2).
d) HC and CO emissions are reduced
to a very low value.
85
-------
B. Explain the construction of monolith and pellet type converters.
1. Monolith converters
MONOLITH CONVERTER
FLOW DIFFUSER
EXHAUST
GASES
HONEYCOMB
MONOLITH
STAINLESS STEEL
SHELL
STAINLESS
STEEL MESH
Figure 10-2
EXHAUST GAS FLOW-THRU
PELLET-STYLE CATALYTIC
CONVERTER
INSULATION
EXHAUST
GASES
\
INSULATION
ALUMINUM OXIDE PELLETS COATED
WITH PLATINUM AND PALLADIUM
Figure 10-3
a) Can have one or two ceramic
honey-combed monolith units in
them.
b) The monolith units are cradled
in a stainless steel mesh to
protect them from road shocks.
c) Each monolith unit is covered
with a thin coating of platinum
or a platinum-palladium mixture.
(These elements speed up the
burning or oxidation process.)
d) Exhaust gas enters the conver-
ters, is spread out by the
diffuser and flows through the
honey-combed monoliths where the
HC and CO are more completely
burned.
2. Pellet type converters
a) Contains a bed of small aluminum
oxide pellets that are coated
with platinum or a combination
of platinum-palladium.
b) Exhaust gases enter the conver-
ter and are directed downward
through the coated pellet bed.
c) In the pellet bed oxidation or
burning reduces the amount of HC
and CO in the exhaust.
d) The pellets can be replaced.
Note: Oxidizing catalytic converters do not reduce NO . NO control
X X
will require a reducing converter, not an oxidizing converter.
C. Explain how engine operation affects catalytic converter operation.
1. For burning to occur, oxygen must
be present. Air, which contains
oxygen, is supplied to the conver-
ter by:
86
-------
ADDITIONAL AIR IS SUPPLIED TO
THE CATALYTIC CONVERTER BY=
AIR INJECTION SYSTEMS LEAN AIR-FUEL RATIOS
a) The use of an air injection
system
b) By excess air in the exhaust
system which is determined by
PROPER CARBURETOR ADJUSTMENT.
Figure 10-4
NOTE: A common complaint with catalytic converters is the "Rotten
Egg" odor. This odor results from not enough air being
present in the exhaust system. A complaint odor can normally
be cured by insuring the carburetor is properly adjusted for
both idle speed and air/fuel mixture and/or by insuring the
air injection system is working properly.
D. Explain the purpose for catalytic converter protection systems.
1. Catalytic converters provide a
place for secondary burning of the
exhaust gas.
2. The more unburned fuel (HC) that
enters the converter, the hotter
the secondary burning becomes.
This is especially true of cars
equipped with air injection systems.
3. During certain operating conditions,
such as:
EXCESSIVELY RICH MIXTURES
CAN LEAD TO A DESTROYED
CATALYTIC CONVERTER
Figure 10-5
a) cold starting (when the choke
is applied),
87
-------
b) excessively long periods of
engine idling, and
c) long periods of deceleration,
a rich mixture can overheat the
converter.
4. Catalytic converter protection
systems are designed to protect
the converter from overheating
during these operating conditions.
E. Explain the operation of a catalytic converter protection system.
Note: There are many different variations in protection systems.
The following system is used only as an example. Consult the
manufacturer's service manual before checking or servicing
any catalyst protection system.
1. Protection system operation when
the engine is cold.
THERMACTOR
WITH TVS
SWITCH AND
VACUUM DELAY
VALVE
E6R VALVE AIR CLEANER
TVS SWITCH
BELOW
60° F
BYPASS
VALVE
CHECK
VALVE
AIR \
PUMP
TO SPARK
PORT
COLD
ENGINE
OPERATION
Figure 10-6
a) Below approximately 60°F the TVS
switch in the air cleaner is
closed.
b) Ported or spark port vacuum
(only available when throttle is
opened) is prevented from
reaching the bypass valve.
c) The bypass valve diverts air
pump flow to atmosphere.
d) No air enters the exhaust system,
therefore the secondary burning
in the converter is very limited.
2. Protection system operation at
normal operating temperature.
a) Above approximately 60°F the TVS
switch in the air cleaner opens.
88
-------
THERMACTOR
WITH TVS
SWITCH AND
VACUUM DELAY
VALVE
EGR VALVE AIR CLEANER
TVS SWITCH
ABOVE
60° F
BYPASS
VALVE
AIR\
PUMP
TO SPARK
PORT
WARM
ENGINE
OPERATION
b) When the throttle is opened,
vacuum is allowed through the
TVS switch, through the vacuum
delay valve to the bypass valve.
c) When vacuum is applied to the
bypass valve, air pump flow
enters the exhaust system.
d) The air entering the exhaust
system provides additional
oxygen to the catalytic conver-
ter and secondary burning occurs.
Figure 10-7
THERMACTOR
WITH TVS
SWITCH AND
VACUUM DELAY
VALVE
EGR VALVE
BYPASS
VALVE
AIR \
PUMP
NO VACUUM
SIGNAL
OPERATION DURING
EXTENDED IDLE
OR EXTENDED
DECELERATION
Figure 10-8
3. Protection system operation during
extended idle or extended decelera-
tion
a) When the throttle is closed
vacuum is destroyed in the
vacuum line from the carburetor
to the vacuum delay valve.
b) The vacuum delay valve prevents
vacuum loss to the bypass valve
for approximately 30-60 seconds.
c) During this 30-60 seconds, air
pump flow is being directed to
the exhaust system and secondary
combustion is occuring in the
catalytic converter.
d) After approximately 30-60
seconds, no vacuum remains at
the bypass valve. The bypass
valve dumps the air pump flow to
atmosphere. No additional air
is supplied to the exhaust sys-
tem and secondary burning in the
converter is very small.
Note: Misfiring spark plugs and excessively rich air/fuel mixtures
can damage any catalytic converter. Limit tests that require
spark plug shorting to the amount of time suggested by the
manufacturer in the service manual.
12
-------
HEAT SHIELDS
INTERIOR
INSULATING
PADS.
F. Explain the purpose of exhaust system heat shields.
1. Heat shields are used by some manu-
facturers to protect underbody
components from the higher exhaust
system temperatures that may occur
2. Insure all heat shields are re-
placed when exhaust system servic-
ing is completed.
HEAT
SHIELDS
CATALYTIC
CONVERTER
LOWER SHIELD
Figure 10-9
G. Explain why unleaded fuel must be used in catalytic converter
equipped cars.
1. Leaded gasoline can destroy
LEADED FUEL DESTROYS
CATALYST EFFECTIVENESS
LEAD COATS THE CATALYST
MAKING IT INEFFECTIVE
catalytic converter effectiveness
i) Lead in the exhaust coats the
platinum-palladium coating.
ii) This coating of lead prevents
the catalyst from speeding up
the burning process.
Figure 10-10
H. Explain how catalytic converters can affect HC, CO and NO emissions
and driveability.
1. Oxidizing catalytic converters do
not have any effect on NO
emissions.
2. Converters have no effect on drive-
ability.
90
-------
c) Inspect catalytic converter for
physical damage and overheating.
2. Operational Checks
a) Warm up, zero and span an infra-
red exhaust analyzer.
b) Start engine and bring to
operating temperature.
c) Probe the tailpipe and record
HC-CO at idle.
d) Increase speed to 2000 rpm and
record HC-CO.
Note: If the catalytic converter is operating properly idle CO
readings should be extremely low and HC readings should be
approximately 20 -100 PPM. If readings are higher, (CO
approximately 2-8%, HC 100-400 PPM) use the manufacturer's
procedure for adjusting ignition timing and setting idle speed
and idle air/fuel ratio. Follow the manufacturer's instruc-
tions for checking the air injection system and catalyst
protection system.
91
-------
Have the students fill out the following worksheet in the student
workbook as they perform the tests
Engine
Speed
0
Idle
2000
rpm
Test
Conditions
VISUAL INSPECTION
a) Catalytic Converter (s)
b) AIR Pump
c) Protection Systems
d) Hose Condition
e) Hose Connections
f) Hose routing
OPERATIONAL CHECKS
Tailpipe Analyzer Reading
Tailpipe Analyzer Reading
Pass
Fail
HC
(ppm)
CO
(%)
92
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
EPA-450/3-77-033
2.
3. RECIPIENT'S ACCESSION-NO.
TITLE ANDSUBTITLE
Instructor's Guide for Vehicle Emissions
Control Training
5 REPORT DATE
Novembe r 1977
6. PERFORMING ORGANIZATION CODE
AUTHOR(S)
B.D. Hayes
M.T. Maness
8. PERFORMING ORGANIZATION REPORT NO.
R.A. Ragazzi
PERFORMING ORGANIZATION NAME AND ADDRESS
Department of Industrial Sciences
Colorado State University
Fort Collins, Colorado 80523
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
T900621-01-0
2. SPONSORING AGENCY NAME AND ADDRESS
Control Programs Development Division
Office-of Air Quality Planning and Standards
Office of Air and Waste Management
U.S. Environmental Protection Agency
13. TYPE OF REPORT AND PERIOD COVERED
"F-tnal
14. SPONSORING
EPA
AGENCY CODE
200/04
15. SUPPLEMENTARY NOTES
Research Triangle Park, North Carolina 27711
16. ABSTRACT
It is the intent of this book to explain each basic emissions control system and
some of the more common devices found on today's car. Since it is an instructor's
book it is designed to allow the instructor or facilitator to lead a group of
students through the key points of each emissions control system.
Each basic emissions control system presented has the following information pro-
vided:
Part Identification
System Operation
System Control
System Effects on HC-CO and Driveability
Worksheets
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Hydrocarbons
Carbon Monoxide
Oxides of Nitrogen
Infrared Exhaust Gas Analyzer
Ignition
Carburetion
Positive Crankcase Ventilation
18. DISTRIBUTION STATEMENT
Release Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
100
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
.S. GOVERNMENT PRINTING OFFICE: 197 8-74 5-
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