INSPECTOR'S GUIDE
FOR VEHICLE EMISSIONS
CONTROL
Colorado
State
University
DEPARTMENT OF INDUSTRIAL SCIENCES
I
5
LU
(9
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INSPECTOR'S GUIDE FOR VEHICLE EMISSIONS CONTROL
Developed by the M.V.E.C. Staff
Department of Industrial Sciences
Colorado State University
Fort Collins, Colorado 80523
B. D. Hayes, Project Director
M. T. Maness, Associate Project Director
B. D. Lee, Co-Investigator
R. A. Ragazzi, Co-Investigator
July, 1978
Funded Through
Project Grant
31-1972-1167 T900621-01-0
33-1972-1191 T900718-01-0
Environmental Protection Agency
Research Triangle Park, North Carolina
27711
Bruce Hogarth, Director
COPYRIGHT ©
Colorado State University
1977
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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.
DISCLAIMER
This is not an official policy and standards document. The
opinions, findings, and conclusions are those of the authors
and not necessarily those of the Environmental Protection
Agency. Every attempt has been made to represent the present
state of the art as well as subject areas still under evalua-
tion. Any mention of products or organizations does not
constitute endorsement by the United States Environmental
Protection Agency.
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INTRODUCTION
The objective of this material is to give the automotive emissions
control inspector the technical and background knowledge needed to
perform a satisfactory emissions inspection on an automobile. This is,
however, limited to taking an exhaust sample and reading the results on
an emissions analyzer. This material does not contain the standards set
by state or federal government. The background material contained
herein will provide the inspector with basic general information about
automotive emissions and automotive emissions controls. It is in no
way conclusive and should be used only to help the inspector acquire a
job entry level of proficiency.
The overall objectives of this packet are to provide the basic knowledge
needed to inspect a vehicle for motor vehicle emissions control. Since
passage of the Clean Air Act, much emphasis has been placed on automotive
emissions control devices. It is important that the emissions inspector
have a basic understanding of these devices, their purposes, and functions
to provide meaningful dialogue to the automobile owner as questions arise.
These instructional materials provide the inspector with technical infor-
mation on emissions control systems and related narratives on the infrared
analyzer. The knowledge gained by studying this material should provide the
inspector with the basic information needed to understand the concepts of
the various emissions control systems presently on automobiles. It should
also provide a basic understanding of the cause of vehicle emissions and
a basic understanding of how the infrared analyzer is used to determine the
amount of HC and CO emissions produced by a vehicle. Proficiency on the
use of the analyzer can be gained only through experience.
A gaseous ghost named VEC (Vehicle Emissions Control) is used in many of
the illustrations. This method of presentation is used to visually
emphasize points which are basic and considered important for an under-
standing of the concept.
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ASSUMPTIONS
The following assumptions were made in the development of this material.
1. These materials are designed for inspector's use.
2. The inspector will not necessarily have to do any repair work.
3. The inspector will have state and/or federal emissions
standards available.
4. The inspector will have the necessary rules and regulations
governing emissions inspection for that particular area in
which he is working.
5. The inspector may provide advice to the vehicle owner concern-
ing possible causes for the failure of an automobile and
actions that need to be taken to correct identified problems.
6. The inspector will have had proper instruction on the use,
calibration and maintenance of the exhaust gas analyzer and
have the proper instruction book for the analyzer.
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CONTENTS
Page
CHAPTER 1
Inspection/Maintenance Programs 1
Purpose of Inspect!on/Maintenace Programs 2
Reasons Why Vehicles Fail Emissions Inspection 2
Advantages of Inspection/Maintenance Programs 2
Components of an Inspection Program 3
-Types of Inspection- 3
Idle Mode Test 3
Loaded Mode Test 4
-Approaches to Accomplishing Inspections 6
-Advantages and Disadvantages of Inspection Program .... 6
Centralized Inspection 6
Decentralized Inspection 7
-Types of Emissions Inspectors 8
-Needed Emissions Testing Instrumentation- 9
Exhaust Gas Analyzers 9
Chassis Dynamometer 10
CHAPTER 2
Cause and Effect of Automobile Emissions 11
Smog 14
Cause of Hydrocarbon Emissions 15
Effects of Hydrocarbon Emissions 19
Cause of NO Emissions 19
X
Effects of NO Emissions 20
/\
Cause of Carbon Monoxide Emissions 20
Effect of Carbon Monoxide Emissions 22
Cause of Particulate Emissions 22
Effects of Particulate Emissions 23
Cause of SO Emissions 23
X
Effect of SO Emissions 24
/\
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Page
CHAPTER 3
The Nondispersive Infrared Gas Analyzer and Its Use 27
Infrared Exhaust Gas Analyzer 28
-Background Information- 28
Typical Meters and Controls 30
Connection, Warm-up and Calibration 32
Meter Readings and Probable Malfunctions 33
CHAPTER 4
Emissions Control Systems 41
Positive Crankcase Ventilation System 42
Thermostatic Air Cleaner 46
Air Injection Reaction 51
Fuel Evaporative Control 65
Exhaust Gas Recirculation 79
Spark Control 87
Catalytic Converter System 105
VI
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CHAPTER 1
INSPECTION/MAINTENANCE PROGRAMS
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PURPOSE OF INSPECTION/MAINTENANCE PROGRAMS
An Inspection Maintenance (I/M) program is one method that can be uti-
lized to aid in meeting National Ambient Air Quality Standards (NAAQS)
for mobile source related pollutants. I/M programs are composed of two
basic functions. The first is inspection. The inspection phase consists
of checking the vehicle exhaust to determine if the exhaust gases exceed
specified standards for hydrocarbons (HC) and carbon monoxide (CO) emis-
sions. The second phase is the maintenance of the vehicle. This takes
into account the diagnosis, adjustment, parts replacement or repairs
necessary to bring the vehicle's exhaust emissions to or below specified
standards.
I/M programs are a logical extension of the Federal Motor Vehicle Emis-
sions Control Program (FMVCP). The FMVCP provides the public with ve-
hicles that meet low emissions standards. This is accomplished through
certification of new vehicle prototypes to ensure they meet federal
standards, selective enforcement auditing of production vehicles and
recalling of vehicle types that fail in-use surveillance checks.
REASONS WHY VEHICLES FAIL EMISSIONS INSPECTION
A large number of vehicles purchased by the public do not continue to
meet emissions standards. Some of the reasons for failing to meet
emissions standards are:
1) Because of disabled emissions control systems.
2) Because of adjustments made to various engine parameters
not in accordance with manufacturers' specifications.
3) Because owners are not aware of, or choose to ignore, manu-
facturers' suggested vehicle maintenance schedules.
ADVANTAGES OF INSPECTION/MAINTENANCE PROGRAMS
I/M programs provide some definite advantages over alternative strat-
egies such as mass transit, parking control and car and van pooling.
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I/M programs offer the following advantages:
1) I/M is the least disruptive for today's lifestyle, therefore, it
is the most easily accepted method by the public for reducing
motor vehicle related pollutants.
2) I/M programs tend to provide the incentive for the public to keep
their vehicles better maintained and tuned, and in this respect
supplement the FMVCP.
3) I/M programs are a deterrent to tampering. As of September, 1977,
thirty states had anti-tampering laws on the books. These laws
are ineffective without an I/M program. A tampering inspection
incorporated into an I/M program would serve as a deterrent to
tampering and put teeth into the existing laws.
4) I/M programs are presently in operation in various cities and
states across the nation. In this respect I/M programs are not
an unknown entity. Considerable data is available related to
I/M program implementation and operation.
5) I/M programs have been successful in reducing motor vehicle
related pollutants. In this respect it is a way for Air Quality
Control Regions (AQCR) to implement a structure to aid in reaching
the air quality standards requirement under Section 110 of the
Clean Air Act.
COMPONENTS OF AN INSPECTION PROGRAM
- Types of Inspection -
The minimum requirements of a workable vehicle emissions inspection pro-
gram are that the inspection is short, applicable to warmed-up vehicles
and that it is able to identify high emitting vehicles. Two testing
procedures which satisfy these criteria are the idle mode and the loaded
mode tests.
Idle Mode Test
The idle mode test is used to determine the amount of hydrocarbon (HC)
and carbon monoxide (CO) emissions produced from the exhaust systems of
vehicles. The test is made with the vehicle in a neutral gear or park
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and the engine at idle. Often,emissions levels are recorded at the
manufacturer's recommended idle, then the engine speed is increased to
approximately 2250 revolutions per minute (rpm) for a high idle speed
test. Often,the standards must be met at both levels. The test is
conducted utilizing an HC and CO exhaust gas analyzer which samples
the exhaust emissions by the induction of a probe in the exhaust
system.
The idle mode test provides a viable method for identifying vehicles
with high emissions levels. The test procedure is simple to perform
and requires relatively little technician training. Inspection lanes
using this method can accomodate a greater capacity, thus resulting in
lower operating cost per vehicle inspection. An additional advantage
is that the procedure can be easily duplicated at repair facilities to
confirm that emissions related repair and maintenance has been success-
ful.
Loaded Mode Test
There are two types of loaded mode tests - the steady state and the
transient. The transient type is not presently being used in any of
the existing I/M programs and will not be discussed in this presenta-
tion. For additional information refer to the EPA publication 400-2-
76-001 "Information Document on Automobile Emissions Inspection and
Maintenance Programs," Section 4.
The steady state loaded mode test samples the exhaust emissions with
the vehicle in a forward drive gear simulating a driving condition.
Emissions are tested at high cruise, low cruise and idle mode operating
states. A chassis dynamometer is used to load the vehicle and simulate
these conditions. Readings are taken in each mode after the emissions
stabilize by utilizing the volumetric procedure, i.e. by a standard
exhaust emissions analyzer.
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The loaded mode testing provides a better indication of total emissions
because it includes the simulation of an actual driving condition. In
addition, the simulation has the capability of providing better diagnostic
information for a "trained" mechanic in terms of actual engine malfunctions
and misadjustments. These advantages come at the expense of greater test-
ing cost due to the need of a chassis dynamometer and in some cases a
NO analyzer along with increased time to perform the test.
A
A summary of the idle mode and steady state loaded mode testing character-
istics are shown in the following illustration.
CHARACTERISTICS OF IDLE MODE AND LOADED MODE TESTING
Idle Mode Testing
Loaded Mode Testing
(Steady State)
1. Simple test procedure
which requires minimum
training for inspectors.
2. Carburetor adjustments
can be made during test.
3. Malfunctions that occur
under loaded conditions
may not be detected.
4. Requires minimal test
time and equipment.
5. Diagnosis on some engine
misadjustments and mal-
functions.
6. Can be duplicated by either
public or private test sys-
tems and repair facilities.
1. Requires more test time.
Additional training for
inspectors.
2. Includes idle test.
3. Engine operated under
simulated road cruise
conditions.
4. Requires dynamometers and
other additional equipment
5. Additional diagnostic
information to repair
facility.
6. Test cannot be duplicated
in most repair facilities
due to lack of dynamometer
Kincannon, Benjamin and Castaline, Alan, Information Document
on Automobile Emissions Inspection and Maintenance, U.S. Environ-
mental Protection Agency, February 1978, p. 23
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- Approaches to Accomplishing Inspections -
There are five recognized approaches used to accomplish emissions inspec-
tions at the present time. These approaches are as follows:
1) Idle mode test conducted at state inspection stations.
2) Idle mode test conducted at inspection stations operated
by a contractor to the state.
3) Idle mode test conducted at privately owned and operated
new car dealerships, garages and service stations.
4) Loaded mode test conducted at state inspection stations.
5) Loaded mode test conducted at inspection stations operated
by a contractor to the state.
These approaches can be administered and conducted at either a network
of centralized inspection lanes or a network of certified private ga-
rages. A public authority can be delegated the responsibility of estab-
lishing the network of centralized inspection lanes, or a contractor can
be commissioned to design, finance, construct and operate the program.
The decentralized approach can be accomplished by licensing and/or cer-
tifying private garages, service stations and new car dealerships to
operate the program utilizing their existing facilities. These facil-
ities should be monitored by and accountable to a public authority who
is responsible for the overall program administration. At least one
state, New Jersey, has a combination of these approaches.
- Advantages and Disadvantages of Inspection Approaches -
The inspection portion of an I/M program can be accomplished by a central
ized inspection facility or a decentralized network of inspection facil-
ities. The advantages and disadvantages of each are as follows.
Centralized Inspection
The centralized inspection consists of a number of contractor or state
operated inspection facilities. The facilities are normally located in
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such a manner as to be readily accessible to a large number of motorists
The centralized inspection systems offer the following advantages:
1) High level of quality control - procedures are specified
and followed to insure uniformity of the inspection process.
2) Efficient data collection and handling -pre and post
emissions data must be collected and analyzed before
necessary adjustments can be made to a program.
3) Ease of monitoring - a small number of inspection facil-
ities minimizes the time and effort required by the
governing agency to complete required inspections of
inspecting facilities.
Following are some of the disadvantages of centralized inspection:
1) Locations often not convenient to all people - a number
of people will have to travel out of their way to have
their vehicles inspected.
2) Long waiting lines - when a small number of inspection
facilities are inspecting a large number of vehicles,
long waiting lines often result.
3) Inconvenience of repair after failure - Automobile must be
taken to private commercial garages for repair, then brought
back to inspecting facility for re-inspection if repairs
are mandatory.
Decentralized inspection is accomplished by private commercial garages.
The decentralized inspection offers the following advantages.
1) * Large number of inspection sites - greater convenience to the
vehicle owner if offered because of the increased probability
of an inspection facility being close to home or office.
2) Small or no waiting lines - the larger number of inspection
sites are able to inspect a large number of vehicles without
long waiting lines.
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3) Convenience of repair - in addition to performing inspections,
repairs and or adjustments are accomplished at the inspection
site. This eliminates the need for a return trip to have a
vehicle reinspected.
The following are some of the disadvantages of a decentralized inspec-
tion system.
1) Inconsistent quality - the inspection procedure will vary
from garage to garage.
2) Increased licensing - a large number of repair facilities
must be licensed to perform inspections. This also results
in subsequent difficulties in inspecting the facilities for
compliance.
3) Data handling and collection - the increased number of
inspection stations and people involved increase the
difficulty of data collection.
4) Referee stations - decentralized inspection still requires
a state operated referee station to handle complaints and
problems that cannot be resolved at the private commercial
garage.
NOTE: EPA stipulates that each licensed inspection
facility be inspected at least once every 90
days. Unless these precautions are taken the
effectiveness of a decentralized I/M approach
could be minimal.
- Types of Emissions Inspectors -
There are basically two types of vehicle emissions inspectors involved
in existing emissions inspection programs. These can be classified as
inspectors who work in centralized inspection facilities and inspectors
who work in decentralized facilities. Normally both types of emissions
inspectors are testing vehicles in an idle mode condition using an infra^
red exhaust gas analyzer.
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The major difference in the two types of emissions inspectors is deter-
mined by the possible involvement of the inspector after a vehicle has
not passed an emissions inspection and the level of training required
for this involvement.
Centralized inspectors are mainly responsible for the initial emissions
inspection of the vehicle. Their responsibility lies in providing an
accurate emissions inspection and maintaining records of the inspection
as designated by the procedures, rules, and regulations normally estab-
lished by a state pollution control agency. They have no responsibility
for bringing a failed vehicle into compliance.
The decentralized inspector has the same responsibility as the centralized
inspector with respect to the inspection process. However, a large per-
centage of the decentralized inspectors are mechanics who should be qual-
ified in the repair of vehicles which fail because they do not comply with
established vehicle emissions standards of the inspectors program. This
normally means that the decentralized inspector should be qualified to
repair the vehicle once it has failed a vehicle emissions inspection.
- Needed Emissions Testing Instrumentation -
The emissions testing instrumentation required is dependent upon the
emissions testing procedure selected for use. As mentioned previously,
an idle mode test requires only an exhaust gas analyzer while the loaded
mode test has the additional requirement of a chassis dynamometer.
Exhaust Gas Analyzers
The exhaust gas analyzer is central to the objectives of an Inspection
and Maintenance program. The instrument must be reliable and be easily
calibrated in order to assure the quality of emissions testing. Accuracy
and repeatability of all inspection lanes and repair industry analyzers
are crucial to system efficiency.
The use of the basic analyzer is quite simple. The probe is inserted
into the exhaust system and samples pollutants which are read on the
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meters. One meter indicates the carbon monoxide concentration, and
the other indicates the concentration of hydrocarbons in the vehicle
exhaust. Additional information on the use of the exhaust gas analyzer
is presented in Chapter Three.
The potential for significant variability in emissions measurements
exists among instruments manufactured by either the same or different
manufacturers. Because of this variability, basic specification
criteria have been developed to minimize the effects. Various public
agencies have performed analyzer certification programs, distributing
to the repair industry and others their lists of approved exhaust gas
analyzers.
As with other types of analytic equipment, periodic maintenance and
calibration are essential if accurate measures of emissions are to be
obtained from the analyzer.
Chassis Dynamometer
A chassis dynamometer is required, in addition to an emissions analyzer,
if a loaded mode test is performed. The dynamometer consists of two
rollers, upon which a vehicle's driving wheels are placed. As the
wheels of the vehicle are rotated, the dynamometer produces a drag on
the engine, thus simulating actual on-the-road operation.
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CHAPTER 2
THE CAUSE AND EFFECT OF AUTOMOBILE EMISSIONS
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FIGURE 2-1
Perfectly pure air, containing approximately 78% nitrogen, 21% oxygen and
1% other inert, harmless gases, is very rare today and probably has been
very rare for many centuries. Air pollution has always existed in one
form or another. In nature is has come from volcanoes, decaying vegeta-
tion as well as our forests of evergreen trees. This type of air pollu-
tion is a product of nature and there is no known way we can control it.
The types of air pollution we can control are the ones that we cause.
One of these, in particular, is the pollution from automobiles. It has
been said that the automobile contributes heavily to the total pollutants
caused by man. Approximately one-half of the total hydrocarbons (HC),
more than three-quarters of the total carbon monoxide (CO) and nearly
one-half of the oxides of nitrogen (NO ) emissions come from automobiles.
/\
(See Figure 2-2). This is a significant contribution.
Another problem is that most of this contribution is made in larger cities
where the majority of people and automobiles congregate (Figure 2-3). The
very design of cities with their tall buildings and relatively narrow
streets tends to limit air movement which traps and concentrates these
pollutants. This is one reason why levels of certain pollutants climb
above safe maximum limits.
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POLLUTANTS
CAUSED
BY
MOTOR
VEHICLES
TOTAL POLLUTANTS CAUSED BY MAN
FIGURE 2-2
FIGURE 2-3
The problem, however, does not stay just in the cities and the surrounding
urban areas. It can be moved great distances by atmospheric conditions
such as the wind. Pollutants have been detected in towns forty to one
hundred miles from major metropolitan areas. These towns, although far
removed from the cities, actually exceed the same safe limits for certain
pollutants.
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The Environmental Protection Agency (EPA) has been assigned the job of
establishing air quality standards. The standards, established by the
EPA, are designed to protect our health. In order to do this, the EPA
and the federal government deemed it necessary to establish limits for
the amount of pollutants emitted from stationary and mobile sources.
The largest mobile source is the automobile.
In order to meet the limits set by the EPA, the automobile manufacturers
had to redesign parts of the internal combustion engine. They also had
to develop various emissions control systems for the internal combustion
engine. It is important that the inspector have a basic knowledge of
these emissions systems so that he can provide meaningful dialogue to the
automobile owner as questions arise about the inspection process and
corrective measures.
Let's look at some of the air pollution problems that are being talked
about ahd examine some cause and effect relationships concerning the
automobile.
SMOG
One air pollution problem is commonly referred to as "smog." There are
two types of smog, sulfurous smog and photochemical smog. Both of these
will be discussed. The word "smog" was originally formed from two words,
smoke and fog. The correct name for this type of smog is "sulfurous smog"
(Figure 2-4).
SMOG
SMOKE + FOG = SULFUROUS SMOG
FIGURE 2-4
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As its name suggests, it is a combination of sulfur-bearing pollutants.
Sulfur is found in all fossil fuels, whether they are coal or oil. This
type of air pollution has been known for over 600 years. The automobile's
contribution to this type of smog is negligible.
Photochemical smog, however, is related to the automobile. Photochemical
or "Los Angeles" type smog results from hydrocarbons (HC) and oxides of
nitrogen (NO ) changing chemically in the presence of sunlight (Figure 2-5)
A
HYDROCARBONS + OXIDES OF NITROGEN +
SUNLIGHT = SMOG
FIGURE 2-5
One main source of these hydrocarbons and oxides of nitrogen is the
internal combustion engine found in motor vehicles.
CAUSE OF HYDROCARBON EMISSIONS
Motor vehicles use gasoline, a petroleum product, for fuel. Gasoline,
like all petroleum products, is comprised of hundreds of hydrocarbon
compounds. In the internal combustion engine, 100% or complete combus-
tion does not occur. Consequently, some unburned hydrocarbons are
exhausted to the atmosphere. One of the causes of unburned hydrocarbon
emissions is a phenomenon called "quenching" (Figure 2-6). Quenching is
what happens to a flame in the combustion chamber as it approaches the
relatively cool metal surfaces. The flame does not burn right up next
15
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FIGURE 2-6
to these cool metal surfaces. It goes out, or is "quenched" by these
cool areas. The failure of the flame to burn next to the metal surfaces
leaves a small amount of unburned fuel or hydrocarbons in this area.
This quenching action also occurs in small areas or cavities in the
combustion area. One such area is where the head gasket seals the cylin-
der head to the block. Another area is between the top of the piston and
the first compression ring. Since the flame does not burn into these
areas, there is a small amount of unburned fuel from each area that is
exhausted to the atmosphere.
Another cause of unburned hydrocarbons is due to combustion chamber
deposits (Figure 2-7). These deposits are porous. As the piston comes
up on the compression stroke, some fuel is forced into these deposits.
This absorbed fuel never burns, but comes out of these deposits late in
the power stroke, or during the exhaust stroke, and is discharged to the
atmosphere on the exhaust stroke.
Quenching and combustion chamber deposits are not the only cause of
unburned hydrocarbons. The ignition system can cause a significant
increase in hydrocarbon emissions. If any part of the ignition system,
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-DEPOSITS
\ ^
FIGURE 2-7
such as the points, becomes worn or out of adjustment the result could
be a weak spark or no spark at all. This will lead to either incomplete
combustion or a misfire. Either condition will result in the emissions
of unburned hydrocarbons (Figure 2-8).
EXHAUST MANIFOLD
o
0 0 0 °
' o
o
o
UNBURNED FUEL
MISFIRE = UNBURNED FUEL
FIGURE 2-8
17
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The temperature of the air/fuel mixture can also have an effect on unburned
hydrocarbon emissions. If the fuel and air temperatures are low, poor
mixing of the air and fuel result. This poor mixing of air and fuel can
result in concentrations of rich and lean mixtures in the intake manifold.
When these rich or lean concentrations are drawn into the cylinder, they
do not burn evenly. This results in the emissions of unburned hydrocarbons.
Another cause of unburned hydrocarbons is the carburetor. If the carbu-
retor is adjusted too rich, there is not enough oxygen to completely burn
the fuel. This unburned fuel results in hydrocarbon emissions. If the
mixture is set too lean, the fuel may be so diluted with air that it will
not ignite. The result is a misfire, and the amount of fuel that did not
burn is exhausted to the atmosphere (Figure 2-9).
FUEL
INTAKE
VALVE
CARBURETOR
RICH
MIXTURE
•^xj
o
LEAN MIXTURE
EXHAUST GAS DILUTION
FIGURE 2-9
An additional cause of unburned hydrocarbons is excessive exhaust gas
dilution. This condition occurs during periods of high intake manifold
vacuum, such as engine idle or deceleration. Dilution of the air/fuel
mixture results in a mixture that may not burn completely or may cause
a complete misfire.
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EFFECTS OF HYDROCARBON EMISSIONS
One effect of hydrocarbon emissions has already been mentioned. That is
the chemical combustion of hydrocarbons and oxides of nitrogen in the
presence of sunlight which results in photochemical smog. Some of the
unburned hydrocarbons that are emitted are very chemically active. Some
combine with oxides of nitrogen and form photochemical smog. Others
remain in the air and act as an irritant to the eyes (Figure 2-10).
FIGURE 2-10
These are the heavier hydrocarbons or the aromatics. One of these heavier
hydrocarbons, benzo-a-pyrene, is also suspected of being a cancer-causing
agent or a carcinogen.
CAUSE OF NOX EMISSIONS
Another pollutant the automobile emits is NO or oxides of nitmgen. Air
X
is made up of approximately 78% nitrogen, 21% oxygen and 1% of other
gases. This air is drawn into the engine and mixed with fuel. This air/
fuel mixture is ignited and temperatures in excess of 4500°F (2482°C) may be
reached. At temperatures above approximately 2500°F (1371°C), nitric oxide
(NO) is formed very rapidly from the nitrogen and oxygen in the air. The
formation of nitric oxide (NO) is dependent on temperature. Any engine
variable that causes an increase in temperature above approximately 2500°F
(1371°C) will cause an increase in nitric oxide (NO) emissions (Figure 2-11)
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HIGH TEMPERATURE 8
FIGURE 2-11
EFFECTS OF NOX EMISSIONS
Oxides of nitrogen or NO are composed of about 97-98% nitric oxide (NO)
A
and about 2-3% nitrogen dioxide (NOJ. Nitric oxide is a colorless gas,
but when it is exhausted to atmosphere it combines with oxygen (02) and
forms nitrogen dioxide (N02). Nitrogen dioxide (N02) is a brownish
color. The nitrogen dioxide (N02) then combines with certain chemically
active hydrocarbons in the presence of sunlight and causes the formation
of photochemical smog.
Some of the nitrogen dioxide is broken apart by sunlight to form nitric
oxide and oxygen (N02 + sunlight — »• NO + 0). This single oxygen (0)
atom combines with diatomic oxygen (02) to form ozone (0-). Ozone, an
odorous gas, is one of the smells associated with smog. Ozone also acts
as an irritant to the lung tissues and the eyes. Ozone also deteriorates
rubber products rapidly, and affects the growth of some crops and plants
(Figure 2-12).
CAUSE OF CARBON MONOXIDE EMISSIONS
Carbon monoxide is another pollutant that originates in the combustion
process. Carbon monoxide (CO) is formed when there is not enough oxygen
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FIGURE 2-12
present to convert carbon (C) to carbon dioxide (C02). As the air/fuel
ratio becomes richer than approximately 15:1, there is not enough oxygen
present to complete the combustion process (Figure 2-13). This shortage
RICH AIR/FUEL MIXTURE
FIGURE 2-13
of oxygen results in an incomplete conversion of carbon (C) to carbon
dioxide (C02). An increase in CO emissions is normally accompanied by
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an increase in HC emissions. This is because of the lack of oxygen
necessary to completely burn all the fuel mixture.
EFFECT OF CARBON MONOXIDE EMISSIONS
Carbon monoxide is an odorless, colorless, toxic gas. When carbon mon-
oxide is inhaled into the lungs and transferred to the blood stream, it
takes the place of oxygen in the red blood cells. The amount of oxygen
being supplied to the body is reduced. This lack of oxygen to the body
can cause headaches, reduce mental alertness, and even cause death if
carbon monoxide concentrations are high enough (Figure 2-14).
FIGURE 2-14
Carbon monoxide also increases the rate at which photochemical smog is
formed. It does this by speeding up the conversion of nitric oxide (NO)
to nitrogen dioxide (N02). Carbon monoxide (CO) speeds up this reaction
by combining with oxygen (02) and nitric oxide (NO) to produce carbon
dioxide (C02) and nitrogen dioxide (N02) (CO + 02 + NO —> C0? + NO ).
CAUSE OF PARTICULA.TE EMISSIONS
Particulate emissions also come from the automobile engine. Although
there is no limit for particulates at the present time, they are worth
discussing. Particulate emissions result primarily from hydrocarbon
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fuels and certain fuel additives. The lead particulates originate
from the tetra ethyl lead Pb(C2H5)4 that is added to the fuel to raise
the octane rating (Figure 2-15).
^CARBON-BURNED FUEL
FIGURE 2-15
EFFECTS OF PARTICULATE EMISSIONS
Small particulates that are suspended in the atmosphere are one of the
causes of the reduced visibility that accompanies photochemical smog.
Lead particulates that are emitted to the atmosphere are suspected of
being a health hazard in two ways: (1) respiratory intake of airborne
lead during breathing and (2) contamination of food by lead that has
settled in the soil (Figure 2-16).
CAUSE OF SOX EMISSIONS
Another air pollution problem has recently been discovered. This is the
problem of oxides of sulfur (SO ) emissions. This problem became evident
/\
with the introduction of catalytic converters. Oxides of sulfur result
from the small amount of sulfur present in gasoline. Normally, the
sulfur content of gasoline is less than 0.1%. However, this small amount
of sulfur is emitted from the engine exhaust to the atmosphere (Figure
2-17).
23
-------
PARTICULATE EMISSIONS
FIGURE 2-16
FUEL
CHEMICALS THAT
MAKE UP GASOLINE
HYDROCARBONS
+
ANTI-KNOCK ADDITIVES
+
IMPURITIES SUCH AS
SULFUR
FIGURE 2-17
EFFECT OF SOX EMISSIONS
The major problem with SO emissions in motor vehicles is the production
A
of a sulfuric acid mist. The problem occurs primarily from vehicles
equipped with catalytic converters. These converters provide an oxidizing
24
-------
atmosphere that enhances the formation of sulfuric acid from the sulfur
compounds in the fuel. In the catalytic converter, sulfur dioxide (S02)
is converted to sulfur trioxide (S03) in the oxidizing atmosphere of the
converter (2S02 + 02 —> 2S03). Sulfur trioxide (S03) combines with water
(H20 vapor, the water vapor coming from the oxidation of hydrocarbons),
and forms a sulfuric acid (H2$04) mist. Sulfuric acid is very corrosive.
Consequently, it will deteriorate textiles, building materials and
vegetation. It is also very harmful to living tissue (Figure 2-18).
SULFURIC ACID MIST
FIGURE 2-18
25
-------
CHAPTER 3
THE NONDISPERSIVE INFRARED
GAS ANALYZER AND ITS USE
-------
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 analyzer 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 readings
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 infor-
mation for vehicle emissions inspection and diagnostic work. However,
to utilize the infrared in this manner requires an -understanding of hydro-
carbons (HC) and carbon monoxide (CO). It may be necessary at this point
to review Chapter Two where emissions are covered. 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 the atmosphere.
Understanding HC, CO and the correct use of the infrared exhaust gas
analyzer is necessary to perform proper emissions inspections and pro-
vide meaningful information to the automobile owner as questions arise.
Figure 3-1 shows the basic parts of an infrared exhaust gas analyzer.
This is provided to give a reference of basic theory of construction of
an analyzer. Normally manufacturers of analyzers provide more in-depth
information on the specific analyzer which the inspector will be using.
The basic parts of an infrared exhaust gas analyzer and their functions
are:
1) Infared Heater - Provides a constant source of infrared waves
or energy through the reference and sample cells.
2) Chopper Wheel - A segmented disc driven by a motor. The disc
constantly interrupts the infrared signal. This provides a
pulsating infrared signal.
28
-------
CHOPPER
AMPLE J
IN
SAMPLE
CELL
AMPLE i
OUT n
DETECTOR —
I
1
/SEALED
'REFERENCE
CELL
- SIGNAL TO PREAMP
FIGURE 3-1
3) Sample Cell - A cell that the exhaust gases flow through.
Infrared or energy is absorbed as HC and CO pass through
the sample cell.
4) Reference Cell - A cell that contains n£ HC or CO. No
infrared waves or energy is absorbed in this cell.
5) Detector - Changes the infrared signal to an electrical
signal.
6) Amplifier - Increases the electrical signal from the
detector to provide meter readings.
Figure 3-2 shows a picture of the front of a typical analyzer. Although
the different analyzers vary somewhat, the following is representative of
basic meters and controls.
29
-------
TYPICAL METERS AND CONTROLS
Meters
A. Hydrocarbon meter
B. Carbon Monoxide meter
Hydrocarbon-Push Buttons
1. "HI" sets HC meter to read on the 0-2000 PPM scale.
2. "LO" sets HC meter to read on the 0-500 PPM scale.
Mode Control-Push Buttons
3. "OFF" - Turns tester off.
4. "TEST" - Turns tester on in test mode.
5. "ZERO" - Turns tester on to calibration and standby mode.
6. "SPAN" - Depress and hold while adjusting meters to "SPAN SET" line.
Carbon Monoxide-Push Buttons
7- "HI" sets CO meter to read on the 0-10% scale.
8. "LO" sets CO meter to read on the 0-2.5% scale
Rotating Controls
9. "ZERO" - Sets HC meter to Zero set line.
10. "SPAN" - Sets HC meter to Span set line.
11. "ZERO" - Sets CO meter to Zero set line.
12. "SPAN" - Sets CO meter to Span set line.
30
-------
Meter Mechanical Zero
13. Adjusts Mechanical Zero of HC Meter.
14. Adjusts Mechanical Zero of CO Meter.
Exhaust gas samples are continuously delivered to the infrared analyzer
by means of a probe inserted in the vehicle's tailpipe (Figure 3-3). The
exhaust gas is then filtered and the water is removed before being
FIGURE 3-3
conducted into the infrared analyzing device. The infrared analyzing
device determines the exact amount of hydrocarbons and carbon monoxide
contained in the sample. This data is then converted into electrical
signals and displayed on the respective meters.
Before any testing can be done certain precautions must be taken to make
sure the tests made are valid. The analyzer must be warmed up and
prepared for use. Always follow the manufacturer's specifications and
recommendations in preparing the analyzer for use. Although the
different analyzers vary somewhat, the following is a basic procedure
for preparing most infrared exhaust analyzers for use. Refer to Figure
3-4 as you read through this procedure.
31
-------
1.
2.
3.
4.
5.
8.
SPAN SET
HYDROCARBON
2 3 4
CARBON MONOXIDE
-------
METER READINGS AND PROBABLE MALFUNCTIONS
The following illustrations are provided to associate meter readings with
probable malfunctions that can be typically diagnosed with the use of the
infrared gas analyzer. The first illustration indicates a normal range
of reading on the meters. The high or low switch for hydrocarbons and
carbon monoxides will be darkened to illustrate the scale selection of
each meter.
HYDROCARBON
CARBON MONOXIDE
-------
HYDROCARBON
CARBON MONOXIDE
r— HYDROCARBON — ,
HI LO '
•D
ZERO SPAN
0 0
1 — MODE CONTROL .
OFFTESTZEFDSFftN
naan
EXHAUST ANALYZER
I—CARBON MONOXIDE -|
HI LO '
DB
ZERO SPAN
o o
FIGURE 3-6
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
34
-------
HYDROCARBON
CARBON MONOXIDE
|- HYDROCARBON -, . — MODE CONTROL .
HI LO ' OFFTESTZEFDSPAN'
•D nann
ZERO
0
SPAN
O EXHAUST ANALYZER
i— CARBON MONOXIDE-,
HI LO '
D
ZERO
O
•
SPAN
O
FIGURE 3-7
3. Symptoms - Rough idle.
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
35
-------
HYDROCARBON
CARBON MONOXIDE
-------
ago
SPAN SET
HYDROCARBON
CARBON MONOXIDE
-------
HYDROCARBON
CARBON MONOXIDE
©
t— HYDROCARBON — . __ MODE CONTROL ,
HI LO ' OFFTESTZEFOSPAN1
•
ZERO
o
D nann
SPAN
O EXHAUST ANALYZER
r- CARBON MONOXIDE-!
HI LO '
D
ZERO
O
•
SPAN
O
FIGURE 3-10
6. Symptoms - Engine surging, 1500 RPM
a) Erratic EGR valve operation
b) Timing too far advanced
38
-------
HYDROCARBON
CARBON MONOXIDE
r HYDROCARBON _. _. MODE CONTROL ,
HI LO ' OFF TESTZEFC SPAN
n
ZERO
o
• DBDD
SPAN
O EXHAUST ANALYZER
r- CARBON MONOXIDE-,
HI LO
D
ZERO
O
•
SPAN
O
FIGURE 3-11
7. Symptoms - Engine surging, 1500 RPM
a) Carburetion too lean
39
-------
HYDROCARBON
-------
CHAPTER
EMISSIONS CONTROL SYSTEMS
-------
POSITIVE CRANKCASE VENTILATION SYSTEM
POSITIVE CRANKCASE VENTILATION SYSTEM
CARBURETOR
HOSE
BLOW-BY
GASES
FIGURE 4-1
The crankcase ventilation system was the first antipollution device
installed on the automobile. This ventilation system is known by the
letters PCV which stand for Positive Crankcase Ventilation. The PCV system
is very dependable and efficient and requires a minimum of maintenance.
The function of the positive crankcase ventilation system is to prevent the
escape of blowby products to the atmosphere.
During the combustion process higher pressures are developed in the combus-
tion chamber. This high pressure results in leakage or blowby between the
piston rings and the cylinder wall. This blowby occurs during the compres-
sion stroke as shown in Figure 4-2 and in the power stroke as shown in
Figure 4-3.
Blowby gases contain gasoline vapor, hydrocarbons (HC), corrosive acids,
and water. To prevent high crankcase pressure and blowby products from
reacting with the engine lubricant, the engine must be equipped with a
means of crankcase ventilation.
42
-------
FIGURE 4-2
FIGURE 4-3
In pre-emissions control automobiles the blowby products were allowed to
escape to the atmosphere through the open road draft tube. The resulting
pollution from the crankcase amounted to approximately 20% of the total
hydrocarbon (HC) pollution emitted by the automobiles (Figure 4-4).
43
-------
CRANKCASE BLOW-BY=
20% OF TOTAL HC EMISSION
20%
FIGURE 4-4
A closed PCV system is used on all vehicles built in the United States
today. The closed system does not allow blowby gases to be emitted to the
atmosphere under any driving conditions. The blowby gases are consumed by
either entering the intake manifold through the PCV valve at the base of
the carburetor or through a hose from the oil filler cap to the air
cleaner and into the carburetor to be consumed. This system is shown in
Figure 4-5.
PCV VALVE
HOSE
SEALED
OIL DIP
STICK
CLOSED SYSTEM
BLOW-BY GASES
FIGURE 4-5
44
-------
PCV valves are no longer serviceable but are simply replaced. All valves
are identified by the manufacturer's number and in some cases, by a color
code.
NEVER DISCONNECT OR PLUG THE PCV SYSTEM BECAUSE EVERY ENGINE NEEDS CRANK-
CASE VENTILATION. THE PRESSURE IN THE CRANKCASE MUST BE RELIEVED ONE
WAY OR ANOTHER.
Most domestic automotive manufacturers require that the system be inspected
and the PCV valve be replaced at 12,000 to 30,000 miles as specified by
the automobile manufacturer. This maintenance schedule can normally be
found in the automobile owner's manual.
Remember - The PCV system reduces hydrocarbon emissions to atmosphere as
well as preventing oil dilution and sludge formation in the crankcase.
This is accomplished by directing blowby gases in the crankcase back to
the combustion chamber to be burned.
45
-------
THERMOSTATIC AIR CLEANER
COLD r -*
TOENGINE COLD
EXHAUST MANIFOLD
D : xs
ENTERS \
AIR HEATED BY MANIFOLD
TAG REDUCES HC 8 CO
FIGURE 4-6
The Thermostatic Air Cleaner (TAG), also known as heated air control,
provides for adjustment of intake air temperature going to the carburetor.
Figure 4-6 shows the complete system, air cleaner, heat shroud and con-
necting hose. This system reduces hydrocarbons (HC) and carbon monoxide
(CO).
Automotive manufacturers have found several other benefits by preheating
the air before it enters the carburetor. This heated air allows for
better atomization of fuel, better cold engine operation and elimination
of carburetor icing, thus providing smoother engine operation.
The Thermostatic Air Cleaner is a key device in many auto emissions
control systems. Two types are widely used: the thermostatic type as
shown in Figure 4-7 and the air valve type as shown in Figure 4-8.
Regardless of the type of air cleaner, vacuum motor or thermostatic, their
job is the same - to provide for adjustments of intake air temperature.
Each type of thermostatic air cleaner has three modes, or positions of
operation, which are: the cold air delivery mode, the regulating mode,
and the hot air delivery mode.
46
-------
THERMOSTATIC TYPE
FIGURE 4-7
VACUUM MOTOR TYPE
VACUUM MOTOR
TEMR SENSORA
TO EXHAUST
MANIFOLD'
SHROUD
FIGURE 4-8
Figure 4-9 shows a cutaway of a Thermostatic Air Cleaner showing the air
filter, thermostat, air valve door and snorkel. The snorkel admits engine
compartment or fresh air to the air cleaner. This is referred to as cold
air. It is the function of the thermostat acting on the air valve door
to determine whether cold air or heated air from the shroud of the
exhaust manifold is allowed to enter the carburetor.
47
-------
AIR VALVE (DOOR)
SPRING. / AIR FILTER-
THERMOSTAT
TO EXHAUST
MANIFOLD SHROUD
FIGURE 4-9
During cold engine start and warm-up period, the air temperature is below
approximately 105°F or 40.5°C (this temperature will vary slightly for
each application). The thermostat is in a retracted position, or "hot
air mode." Since it is linked to the spring loaded air valve door, it
holds the valve open to manifold heated air (see Figure 4-10).
AIR VALVE (DOOR)
AIR FILTER
FIGURE 4-10
48
-------
This shuts off the cold air and allows only air into the carburetor that
has been preheated by passing over the exhaust manifold.
As the heated air increases in temperature to approximately 105°F or
40.5 C, the thermostat begins to extend and pulls the air valve door
downward allowing some cold air to enter the carburetor. It is then
in the "regulating mode" as shown in Figure 4-11.
REGULATING MODE
FIGURE 4-11
When the temperature reaches approximately 130°F or 54.4°C, the air valve
door is fully opened to cold air and is in the "cold air mode," allowing
only cold air from the snorkel to enter the carburetor. This condition
is shown in Figure 4-12.
Remember - the purpose of temperature controlled air cleaners is to keep
incoming air temperature at approximately 100°F or higher. This temper-
ature enhances a more complete combustion which reduces HC and CO
emissions.
49
-------
COLD AIR MODE
FIGURE 4-12
50
-------
AIR INJECTION REACTION
FIGURE 4-13
The purpose of the air injection system is to reduce carbon monoxide and
hydrocarbon emissions by injecting a flow of air into the hot exhaust
gases. The oxygen (02) in the air combines chemically with the carbon
monoxide (CO) to form carbon dioxide (C0?), a harmless gas. It also
combines with the hydrocarbons (HC) to produce water (H?0) and carbon
dioxide (CCL), usually in vapor form. This process is shown in Figure
4-13. Therefore, the air injection reaction system reduces both hydro-
carbons and carbon monoxide.
Different manufacturers call the air injection system by different names
but the function is the same. American Motors calls it "Air Guard."
Chrysler calls it "Air Injection." Ford calls it "Thermactor."
General Motors calls it "AIR" or "Air Injection Reactor" (Figure 4-14).
Figure 4-15 shows a typical "Air Injection" system and its components.
The air injection system uses an air pump as a source of air. It also
has a diverter valve to prevent backfire in the exhaust system during
deceleration. These parts are shown encircled in Figure 4-16. When the
engine decelerates there is low pressure in the cylinder because the
51
-------
VEHICLE
MANUFACT.
AMERICAN
MOTORS^fcORP
CHR^LER
CORPORATION
pQRD MOTOR
COMPANY
GENERAL
MOTORS CORR
AIR INJECTION
SYSTEM
A.G.
(AIR GUARD)
AIR
INJECTION
THERMACTOR
A 1 R
(AIR INJECTOR
REACTOR) .
FIGURE 4-14
MANIFOLD VACUUM
-SIGNAL LINE
PUMP
DIVERTER
VALVE
MANIFOLD
FIGURE 4-15
throttle valve is closed, preventing air from filling the cylinder on
the intake stroke. Under this condition the mixture is too rich to burn
in the cylinder and a rich air/fuel mixture is pushed into the exhaust
manifold. If the air injection system added air to this mixture, a burn
could take place in the exhaust system causing a backfire. The
52
-------
diverter valve shuts air injection off during the initial 1 to 3 seconds
of deceleration thereby preventing a backfire.
MANIFOLD VACUUM
SIGNAL LINE
DIVERTER
VALVE
MANIFOLD
FIGURE 4-16
After the air flows through the diverter valve, it flows through a hose
or pipe to the check valve. The check valve (Figure 4-17) is open anytime
the pressure in the air injection system is higher than the pressure in
CHECK VALVE
FIGURE 4-17
53
-------
the exhaust system. The check valve prevents the back flow of exhaust
gas in the event of a pump failure or during times when exhaust pressure
is higher than the air injection system pressure.
After the check valve, the air flows into the air injection manifold for
distribution into each exhaust port near the exhaust valve. The pump,
diverter valve, check valve, and injection manifold are connected with
hoses and pipes to complete the system as shown in Figure 4-18.
MANIFOLD VACUUM
SIGNAL LINE
FIGURE 4-18
Figure 4-19 shows an air injection system connected to a V-8 engine. You
will notice it has an air injection manifold for each bank of cylinders.
The air flow during operation is from the pump to the outlet hose,
through the diverter or bypass valve and connecting hose to the check
valve and into the air manifold for distribution to each exhaust valve
port as illustrated in Figure 4-20.
54
-------
FIGURE 4-19
FIGURE 4-20
Figure 4-211llustrates typically how the belt-driven air pump is mounted
on the front of the engine.
Figure 4-22 is a simplified view of the inside of the air pump. The
arrows show the movement of air by the vanes through the pump. The
number of vanes varies from 2 to 5.
55
-------
FIGURE 4-21
CROSS SECTION OF AIR PUMP
VANE
ROTOR
PUMP
HOUSING
VANE SEALS
OUTLET
INLET
FIGURE 4-22
Air enters the air pump in either of two ways. One is by an external
air filter such as shown in Figure 4-23 or through a centrifugal fan
filter shown in Figure 4-24. The centrifugal filter is by far the most
popular.
56
-------
AIR INLET
FIGURE 4-23
AIR INLET
FIGURE 4-24
Output air from the pump (Figure 4-25) leaves the discharge connection
of the pump and flows into the connecting hose leading to the diverter
valve.
57
-------
AIR IN
PULLEY
PUMP
DISCHARGE
TO DIVERTER VALVE
AIR IN
FIGURE 4-25
Two types of valves are used to prevent backfire. These types are shown
in Figure 4-26. One type, the gulp valve, allows pump air to be sent to
the intake manifold on deceleration to dilute the rich mixture preventing
backfire. The diverter valve prevents air from entering the air injection
manifold by venting pump air to the atmosphere during deceleration.
JJi EXTERNAL MUFFLER
GULP VALVE
^-INTERNAL MUFFLER
FIGURE 4-26
58
-------
The gulp valve (Figure 4-27) operates when intake manifold vacuum reaches
about 20-22 inches of mercury (Hg). This vacuum pulls the diaphragm
down against spring force, opening the air valve to vent pump air to
the intake manifold. This venting takes place for 1 to 3 seconds of
initial deceleration which is the critical time for backfire to occur.
INTAKE
MANIFOLD
VACUUM
SIGNAL
AIR FROM
AIR PUMP
AIR DISCHARGE
TO INTAKE
MANIFOLD
'AIR VALVE
FIGURE 4-27
Figure 4-28 shows a cutaway view of the combination diverter pressure
regulator valve. Parts shown are the diaphragm and spring, stem, valve
plates and manifold vacuum entrance.
TIMING
ORIFICE
SPRING
VALVE
PLATES
FIGURE 4-28
59
DIAPHRAGM
ANIFOLD
VACUUM
STEM
-------
When the engine is operating, vacuum is applied to both sides of the
diaphragm equally by means of a timing orifice in the diaphragm. The
diaphragm spring raises the stem and unseats the upper valve plate as
shown in Figure 4-29.
DIAPHRAGM
SPRING
VALVE
PLATES
MANIFOLD
VACUUM
STEM
FIGURE 4-29
The air flow under this condition flows in from the pump through the
diverter valve and into the exhaust manifold or manifolds (Figure 4-30)
TO
EXHAUST
MANIFOLD
EXHAUST
MANIFOLD
FROM
PUMP
FIGURE 4-30
60
-------
During periods of deceleration, higher manifold vacuum is imposed on the
lower side of the diaphragm than on the upper side. The diaphragm forces
the stem and valves to be moved downward against spring force (Figure 4-31)
^^
VENT
SEATED
FIGURE 4-31
When the stem moves down, the upper valve plate seats and the lower valve
plate opens allowing the pump air to vent to atmosphere until the vacuum
on the diaphragm becomes equal on both sides by flow through the diaphragm
timing orifice. When pressure equalizes on both sides of the diaphragm,
the diaphragm spring returns the valve plates to the position shown in
Figure 4-32.
TO
EXHAUST
MANIFOLD
TO
EXHAUST
MANIFOLD
FROM
PUMP
FIGURE 4-32
61
-------
When the engine is turning at a high RPM, excessive pressure is produced.
In the combination diverter and pressure regulator valve, the lower valve
plate is forced down and excessive air pressure is vented to atmosphere
(Figure 4-33).
5PSI
VENT
FIGURE 4-33
Illustration 4-34 shows the relationship of the check valve and air
injection manifold.
CHECK
VALVE-
AIR INJECTION MANIFOLD
FIGURE 4-34
62
-------
Figure 4-35 shows a cutaway view of the check valve and air flow when the
system has higher pressure than the exhaust system.
CHECK VALVE
FIGURE 4-35
Figure 4-36 shows the check valve seated during the time when the exhaust
back pressure is higher than the air pressure from the pump.
FIGL
b3
-------
Illustrated in Figure 4-37 are the air manifolds and tubes as used on a
typical 6 and 8 cylinder engine. Usually one tube is used for each
exhaust port. On some vehicles the manufacturers have omitted one
distribution tube, usually because of design problems.
AIR INJECTION MANIFOLDS
6 CYLINDER
8 CYLINDER
FIGURE 4-37
Remember - The AIR system reduces HC and CO by injecting air into the
exhaust manifold. This added air speeds up the oxidation process of HC
and CO and results in lower emissions.
64
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FUEL EVAPORATIVE CONTROL
3 SOURCES OF AUTO EMISSIONS
FUEL EVAPORATION -
TANK 8 CARBURETOR
20%
CRANKCASE
20%
EXHAUST
60%
FIGURE 4-38
It is estimated that on the pre-emissions controlled automobile about 20%
of all emissions consist of gasoline hydrocarbon vapors that evaporate
from the carburetor and fuel tank.
To eliminate these evaporative losses, automobile manufacturers developed
control systems beginning in 1970 for cars in California. Nationally in
1971, all U.S. automobile manufacturers equipped their vehicles with the
following evaporative control devices:
1) A fuel tank safety filler cap which seals the system.
2) A special fuel tank designed to allow space for fuel expansion.
3) A venting system to carry vapors from the fuel tank to the engine
for eventual burning.
A venting system includes a liquid check valve or a liquid vapor separator
to keep liquid fuel out of the vent lines, a charcoal canister to store
the vapors and connecting lines to carry the vapor from the canister to the
engine for burning (Figure 4-39). Chrysler used a crankcase storage system
for the first two years instead of the canister, but its function was the
same.
65
-------
FUEL EVAPORATION SYSTEM
PURGE
LINE
FUEL TANK
VENT LINE
PRESSURE
VACUUM
SAFETY
FILLER CAP
CHARCOAL
CANISTER
OVERFILL
LIMITING
VALVE
LIQUID
VAPOR
SEPARATOR
FIGURE 4-39
The fuel evaporative emissions control systems used by most U.S. auto-
mobile manufacturers are similar, sometimes almost identical. However,
there are some minor differences, mainly in the name. Following is a list
of names given the fuel evaporative systems by different manufacturers:
American Motors
Chrysler
Ford
General Motors
Foreign
Fuel Tank Vapor Control
Vapor Saver
Evaporation Control System
Evaporative Emissions Control
Fuel Vapor Recovery System
Before emissions control, fuel caps and fuel tanks were vented to allow
raw fuel vapors or even liquid gasoline to escape, unrestricted, into the
atmosphere. An illustration of this system is shown in Figure 4-40.
In the present fuel tank filler cap, a safety pressure relief valve will
open only if pressure from one-half to one psi builds in the tank (Figure
4-41.
66
-------
VENTED GAS CAP
VENTED
CAP
FUEL TANK
FIGURE 4-40
PRESSURE-VACUUM RELIEF CAP
TANK PRESSURE l/z - I PSI
SEALING
GASKET
OUTER SHELL
PRESSURE
SPRING
PRESSURE'
RELIEF
VALVE (OPEN)
VACUUM RELIEF
LOCKING
LIP
VALVE (CLOSED) VACUUM SPRING
FIGURE 4-41
If a vacuum of one-fourth to one-half inch mercury (Hg) buildup occurs,
the safety vacuum relief valve will open to let in some outside air, but
normally the cap is sealed (Figure 4-42).
67
-------
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 4-42
The filler neck on most fuel tanks extends below the top of the tank
preventing the tank from being filled 100%. This provides an expansion
space of 10 to 12% of tank capacity at the top to allow room for the
gasoline to expand when the temperatures increase (See Figure 4-43).
FUEL TANK FILL CONTROL
10-12%
EXPANSION
SPACE \
FILLER
CAP
FILLER
NECK
FUEL
TANK
FUEL
FIGURE 4-43
68
-------
Some models, 1970 and 1971 only, use an inner expansion tank as shown in
Figure4-44, and incorporate a fill control tube with the filler neck. If
fuel continues pumping into the tank above the filler neck, a fill control
tube returns it to the filler neck which shuts off the automatic fill nozzle
SMALL
VENT
HOLES
INTERNAL EXPANSION
TANK
FILL
CONTROL
TUBE
FILLER
NECK
TANK OPEN
AT BOTTOM
FUEL TANK
FIGURE 4-44
With the fuel tank sealed to atmosphere, fuel vapors will collect at the
top of the tank and have only one way to go -- into the venting lines to
be stored in the storage device as shown in Figure 4-45.
SEALED TANK VAPOR PASS TO
CHARCOAL CANISTER
HOSE TO
CHARCOAL
CANISTER
VAPORS TO
CHARCOAL
CANISTER
FUEL
TANK
FIGURE 4-45
69
-------
In tanks without internal or separate expansion tanks, an internal ex-
pansion space must be provided into which fuel or fuel vapor can safely
expand, as illustrated in Figure 4-46. This volume is approximately ten
to twelve percent of the fuel tank volume.
AIR SPACE PROVIDED FOR
FUEL EXPANSION
10-12% OF TANK VOLUME
FUEL
TANK
FUEL
FIGURE 4-46
Some manufacturers, such as Volkswagen, use an external expansion chamber.
In operation, liquid fuel rising from the tank is routed to the expansion
chamber (Figure 4-47). The chamber is designed to permit the passage of
EXTERNAL EXPANSION CHAMBER
EXPANSION
TANK
TO CHARCOAL
CANISTER
TO FUEL PUMP
FUEL
TANK
FIGURE 4-47
70
-------
fuel vapors, but to prevent the passage of liquid fuel. From this
external chamber, the fuel vapors are carried forward into a container
filled with activated charcoal where they are stored when the engine is
not running. The liquid is drained back to the tank.
Because some fuel tanks are flat on top, four vents are used, one in
each corner of the tank. These are connected to a liquid vapor separator
by rubber hoses or metal pipes.
The liquid vapor separator consists of a length of steel tubing which is
mounted at an angle ahead and slightly above the fuel tank. This tubing
holds the four vent lines from the tank and a vent line which leads to
the charcoal canister. See Figure 4-48.
LIQUID VAPOR
SEPARATER
TO CHARCOAL
CANISTER
VAPOR
VENT
LINES
LIQUID
RETURN
LINE
FUEL
TANK
FIGURE 4-48
These lines are of different heights so that the tank will always be
vented, regardless of vehicle position. This way, only the fuel vapors
will be transferred to the storage area. One vent line from the tank is
shorter than the others in order to provide a drain back to the tank for
any liquid fuel which may get into the separator during inclined parking.
The vent to the storage area or charcoal canister is at the highest point
in the separator and has a small orifice to minimize liquid fuel transfer
to the storage area or canister.
71
-------
The next component of the evaporative systems is the vapor storage
canister which uses activated charcoal granules to store the vapors until
they are drawn into the carburetor. The typical canister contains about
one to one and one-half pounds of charcoal which provides an exposed
surface area of about one-quarter square mile, enough to store almost a
cup of liquid fuel when vaporized. This storage canister has two
connections, the vent line from the fuel tank and a connecting vent line
to the carburetor or air cleaner. An illustration of a charcoal
canister is shown in Figure 4-49.
CHARCOAL CANISTER
HOSE
CARBURETOR
OR
AIR CLEANER
CHARCOAL
GRANULES
IOSE TO
FUEL TANK
VENT
-CANISTER
CASE
^-FIBERGLAS
^ FILTER
OUTSIDE AIR
FIGURE 4-49
With the engine running, outside air is drawn through the canister to
remove fuel vapors collected by the charcoal granules. This is called the
evacuation or purge cycle and is illustrated in Figure 4-50.
When the engine is running, and during the purge cycle (Figure 4-51).
outside air is drawn through the fiberglass filter of the canister,
through the carbon granules, picking up fuel vapors and carrying them
to the air cleaner to become a part of the air/fuel mixture to be burned.
72
-------
CANISTER PURGING (ENGINE RUNNING)
VAPOR LINE
TO FUEL
TANK\
OUTSIDE AIR
FIGURE 4-50
TO FUEL
TANK VENT
CHARCOAL
OUTSIDE AIR
FIGURE 4-51
Figure 4-52 shows a cross section of a stamped metal canister with an
open space provided above and below the granules.
A center tube is incorporated which extends to the bottom of the canister.
Air can enter at the top of the tube passing downward to the bottom of
the canister. The canister purge line is externally attached (by hoses)
73
-------
OUTSIDE AIR
HOSE TO
FUEL
HOSE TO
AIR CLEANER
CHARCOAL
GRANULES
FIGURE 4-52
to the carburetor air cleaner or the PCV valve (depending on model
application) .
The vapor is purged out of the canister through the air outlet hose to
the air cleaner (or PCV valve), then through the carubretor and into the
combustion chamber -- where the vapors are consumed in the normal
combustion process.
One method of providing additional storage space for vapor is to vent the
fuel tank to the engine crankcase through the engine valve cover. When
the engine is started, stored vapors are drawn into the engine intake
system through the PCV valve. This "purges" the crankcase of stored
vapor so they are ready for more vapor storage when the engine is turned
off (Figure 4-53).
Vapor which originated in the fuel tank and was separated by the vapor
liquid separator is now stored in the canister. In this system, (Figure
4-54). movement of air through the canister is caused by carburetor
intake air passing over the tube which projects into the carburetor air
cleaner snorkel .
-------
FUEL TANK
FIGURE 4-53
AIR
CLEANER
TANK
CARBON
CANISTER
FIGURE 4-54
This creates a vacuum that moves the vapors out of the canister and into
the air stream entering the snorkel. This system is known as a variable
purge system as it is regulated by the rate of air flow entering the air
cleaner.
Another purging method ties a purge line into the PCV valve line. Purging
air passes to the intake manifold through a small fixed orifice on the
canister outlet. This is known as constant purge and is illustrated in
Figure 4-55.
75
-------
PCV
VALVE
TO
INTAKE
MANIFOLD
-CARBON
CANISTER TANK
FIGURE 4-55
Still another method used by some manufacturers is called the constant
and demand purge system (Figure 4-56). A purge valve at the canister
allows constant purging at a restricted rate through an orifice anytime
the throttle plates are closed and the engine is running. When ported
vacuum is applied to the purge valve, it allows a higher rate of purging
to take place through the hose to intake manifold resulting in demand
) (
*******
VACUUM
\
PURG
1 1 Jtf^
PCV HOSE""""^ —
RESTRICTED
ORIFICES
CARBURETOR
BOWL VENT
CONSTANT ft DEMAND
PURGE SYSTEM
FROM
FUEL
TANK
V
FIGURE 4-56
76
-------
purging. Demand purging is designed to ensure that purging occurs during
conditions of engine operation which will least affect performance, drive-
ability and emissions.
Prior to emissions control regulation, hydrocarbons from the carburetor
bowl were allowed to escape into the atmosphere. The advent of controls
necessitated the venting of the carburetor into the canister and the
removal of the atmospheric venting of the carburetor. Figure 4-57
shows one method of controlling vapors through the carburetor external
vent of an anti-perculation valve. The illustration shows the capped
vent open to allow vapor to the canister.
CARBURETOR
TO CANISTER
TO CARB.
LINKAGE
THROTTLE
CLOSED
FIGURE 4-57
With the throttle in the off-idle position, the anti-perculator valve is
closed. In this operational mode, no escape of fuel vapor occurs.
As a review, we will look at the components of the evaporative system
again: a fuel tank filler cap which seals the system, a special fuel tank
designed to allow space for fuel expansion, and a venting system to carry
vapors from the fuel tank to the charcoal canister and into the engine
for burning (Figure 4-58).
77
-------
VAPOR SAVER SYSTEM
FUEL TANK
VENT LINE
PRESSURE
VACUUM
SAFETY
CAP
CANISTER
OVERFILL
LIMITING
VALVE
LIQUID VAPOR
SEPARATOR
FIGURE 4-58
78
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EXHAUST GAS RECIRCULATION
FIGURE 4-59
EGR or the Exhaust Gas Recirculation system reduces oxides of nitrogen
emissions by recirculating regulated amounts of exhaust gases with the
air/fuel mixture before entering the combustion chamber. As VEC is show-
ing us in Figure 4-59,the air/fuel mixture is diluted with exhaust gases
which reduce the combustion temperature to restrict the formation of
oxides of nitrogen.
VEC points out in Figure 4-60that air is approximately 21% oxygen, 78%
nitrogen, and 1% other harmless gases. Nitrogen is the gas we want to
control. Under atmospheric conditions nitrogen is inert and will not
react with other gases,so it passes through the combustion process un-
changed. However, above 2500°F or 1371°C when air is subjected to hot
combustion pressure, nitrogen is no longer inert. The nitrogen combines
with oxygen to form a variety of other gases called oxides of nitrogen,
all grouped together under the term NOX.
A function of the exhaust gas recirculation system is to reduce combus-
tion temperatures by diluting the air/fuel mixture within the intake
manifold with regulated amounts of exhaust gases. This process is shown
in Figure 4-61. These exhaust gases will not support combustion by
79
-------
AIR
21% = OXYGEN
78% = NITROGEN
I % = OTHER
iTV/
FIGURE 4-60
.CARBURETOR
FUEL
INTAKE
MANIFOLD
EXHAUST
AIR a FUEL
FIGURE 4-61
themselves. This exhaust gas absorbs some of the heat of combustion and
lowers combustion temperatures, thus reducing the formation of NO . The
X
exhaust gas recirculation system recirculates approximately 6 to 14% of
the unburned gases.
80
-------
Exhaust gas recirculation was first used by the auto industry in 1972 to
help the internal combustion engine meet the clean air standards. The
Federal Environmental Protection Agency has established standards that
regulate the amount of NO emitted from automobiles.
/\
The main components of the exhaust gas recirculation system are a flow
control device called the EGR valve and an Exhaust Gas Recirculation
Coolant Temperature Override switch, commonly called an EGR-CTO, and
necessary connecting hoses as shown in Figure 4-62. The connecting hoses
EXHAUST GAS RECIRCULATION
EGR
CTO
SWITCH
CARBURETOR
EGR VALVE \
FIGURE 4-62
route vacuum to the EGR valve through the EGR-CTO switch. This allows
the coolant temperature override switch to block or unblock the vacuum
source to the EGR valve, depending upon the temperature of the engine
coolant.
Let's take a closer look at the EGR valve and the EGR-CTO switch. First,
the EGR valve (Figure 4-63)is a simple vacuum opened - spring closed
valve. A coiled spring located above a flexible diaphragm holds the valve
in a normally closed position. There is a vacuum nipple to accept vacuum,
and a pintle which is simply a metering rod connected to the diaphragm.
81
-------
EGR VALVE
FIGURE 4-63
With no vacuum, the valve is closed. The pintle rests on a seat at the
valve bottom to prevent exhaust gas from flowing through the valve as
illustrated in Figure 4-64.
EGR VALVE (CLOSED)
DIAPHRAGM
SPRING
DIAPHRAGM
PINTLE
SEAT
VACUUM
NIPPLE
PINTLE
FIGURE 4-64
During engine operation, vacuum is supplied to the valve vacuum nipple.
82
-------
This vacuum shown by VEC draws the diaphragm upwards overcoming the spring
force and pulling the pintle off its seat to open the valve (Figure 4-65).
EGR VALVE (OPENS)
DIAPHRAGM
SPRING"
FROM
VACUUM
SOURCE
DIAPHRAGI
PINTLE
PINTLE SEAT
FIGURE 4-65
Exhaust gas is moved by engine intake manifold vacuum from the exhaust
system through the pintle opening and valve passage. This exhaust gas is
mixed in the intake manifold with the fresh air/fuel mixture as shown in
Figure 4-66.
TO
INTAKE
MANIFOLD
•0-
FROM
EXHAUST
PASSAGE
FIGURE 4-66
83
-------
The EGR-coolant temperature override switch is another component in the
exhaust gas recirculation system. This switch (Figure 4-67) is a simple
temperature sensitive vacuum switch that allows the vacuum to be controlled
EXHAUST
GAS
RECIRCULATION
COOLANT
TEMPERATURE
OVERRIDE
SWITCH
FIGURE 4-67
according to the engine coolant temperature. At low temperature, the
ball in the switch blocks vacuum at the lower port from reaching the
center port which is connected to the EGR valve. When coolant tempera-
ture rises, the expansion in the lower chamber pushes up on the shaft
that unseats the ball allowing vacuum to be supplied to the EGR valve.
This improves driveability during the warm-up period.
The exhaust gas recirculation system does not operate at idle or at full
throttle. The addition of exhaust gases at idle will cause a very rough
idle condition. At full throttle, there is insufficient vacuum available
to open the EGR valve.
Two methods are used to regulate the amount of exhaust gases going into
the intake manifold. They are the floor jet method and floor entry
method. The floor jet system (Figure 4-68) meters exhaust gases through
two stainless steel jets in the intake manifold directly beneath the
carburetor primary throttle bores. Intake manifold vacuum continually
84
-------
FLOOR JET EGR SYSTEM
INCOMING
FUEL-AIR ORIFICE
MIXTURE
FLOOR JET
EXHAUST GAS
CROSS-OVER
INTAKE
MANIFOLD
RECIRCULATING
GASES
FIGURE 4-68
draws exhaust gases through the jets but the amount of flow depends upon
the amount of vacuum, size of the floor jets and the amount of exhaust
back pressure.
The other method for permitting exhaust gas entry into the intake manifold
is the floor entry method (Figure 4-69). As you can see, the EGR valve
EXHAUST GAS RECIRCULATION
INCOMING
FUEL-AIR
MIXTURE
EGR VALVE
EXHAUST GAS
CROSS-OVER
RECIRCULATING
GASES
INTAKE
MANIFOLD
FIGURE 4-69
85
-------
allows the exhaust gases to reach the opening in the floor and enter the
intake manifold. The difference between floor jet and floor entry method
is the floor entry opening does not meter the gases. The EGR valve regu-
lates the amount of exhaust gases entering the intake manifold.
Remember - the purpose of the EGR system is to supply in proper propor-
tions, exhaust gas to the air/fuel mixture. This dilution lowers peak
combustion temperatures and reduces NO emissions.
X
36
-------
SPARK CONTROL
FIGURE 4-70
The purpose of the spark control systems is to control the advance
and retard of the spark to improve combustion and reduce the formation
of NO and the HC emissions.
X
Retarded spark increases the exhaust gas temperature which promotes addi-
tional burning of the hydrocarbons (HC) in the exhaust manifold (Figure 4-71)
LARGER
THROTTLE
OPENING
HOTTER EXHAUST
TEMPERATURE
FIGURE 4-71
87
-------
Retarded spark at idle also requires a larger throttle opening to obtain
the desired idle speed. This results in more air entering the combustion
chamber during idle.
It is important to note that vacuum from the engine can be sensed at
different places in the carburetor as shown in Figure 4-72. Intake mani-
fold vacuum is sensed below the throttle plate; therefore, vacuum is
SOURCES OF VACUUM
VENTURI
VACUUM
PORTED
VACUUM
INTAKE
MANIFOLD
VACUUM
FIGURE 4-72
available at idle. Ported vacuum is sensed above the throttle plate and
vacuum is not available until the throttle plate is in an off idle posi-
tion. Venturi vacuum is initiated when greater amounts of air pass through
the venturi portion of the carburetor. This vacuum may reach a maximum of
only 3" to 4" Hg.
Prior to the introduction of the spark control system, vacuum was
allowed to act directly on the vacuum advance unit on the distributor.
The control of vacuum either being allowed or denied to the distributor
is the main purpose of the vacuum solenoid valve (Figure 4-73). This
valve will either allow or stop any vacuum to the distributor advance
unit.
-------
VACUUM ADVANCE
SHUT OFF IN
LOWER GEARS
FIGURE 4-73
The vacuum solenoid valve is basically an on/off vacuum switch. This
valve is controlled electrically through a transmission switch. When
electrical current is applied through the contacts, the coil built into
the solenoid valve is energized. This closes the valve and blocks vacuum
from the carburetor to the solenoid valve distributor port. There is a
filter on the end of the vacuum solenoid valve which allows atmospheric
pressure to enter the valve and bleed the distributor vacuum hose of any
vacuum. The vacuum solenoid valve is located in the vacuum line between
the vacuum source and the vacuum advance unit on the distributor. A
cross section of the vacuum solenoid valve is shown in Figure 4-74.
The vacuum solenoid valve is controlled by a transmission switch. The
transmission switch is used on both the manual transmission and automatic
transmissions. The manual transmission switch is open in high gear
only. The automatic transmission switch is open at approximately 35 MPH
or high gear. See Figure 4-75for an illustration of the manual and
automatic transmission switch.
89
-------
COIL
ROD
VACUUM ADVANCE
SHUT OFF IN
LOWER GEARS
FILTER
FIGURE 4-74
MANUAL AUTOMATIC
TRANSMISSION SWITCH TRANSMISSION SWITCH
(OPENS IN HIGH GEAR) (OPENS AT 35 MPH)
FIGURE 4-75
When the transmission switch opens, it breaks the ground circuit to the
vacuum solenoid valve. When this ground circuit is broken, the vacuum
solenoid valve is de-energized pulling the plunger off its seat (Figure
4-76)and vacuum is allowed to act on the distributor advance unit. When
the transmission switch is closed, the ground circuit is complete, the
vacuum solenoid valve is energized pulling the plunger against its seat,
and vacuum is denied to the distributor advance unit.
90
-------
VACUUM SOLENOID
VALVE (DE-ENERGIZED)
CARBURETOR
VENT
DISTRIBUTOR
FIGURE 4-76
The vacuum solenoid valve has two electrical connections. One is connected
to the ignition switch, the other is connected to the transmission switch
as shown in Figure 4-77.
D
IGNITION
SWITCH
VACUUM
SOLENOID
VALVE
TRANSMISSION
SWITCH
FIGURE 4-77
91
-------
Figure 4-78shows the vacuum solenoid valve connected between the carbu-
retor and the distributor with its terminals connected to the ignition
switch and to the transmission switch. You will notice that vacuum is
being allowed through the vacuum solenoid valve, thus the transmission
swtich is open and the ground circuit has been broken or the vacuum
solenoid valve has been de-energized.
SOLENOID VACUUM
SWITCH
DISTRIBUTOR
TRANSMISSION
SWITCH
CARBURETOR
IGNITION
FIGURE 4-78
When the transmission switch is closed, the vacuum solenoid valve is
energized, thus blocking or denying vacuum from the carburetor to the
distributor (Figure 4-79). The vacuum solenoid valve will allow vacuum
to pass if electric current is being denied to the vacuum solenoid valve.
There are exceptions to this. Some vacuum solenoid valves allow vacuum
advance to the distributor when they are energized.
Let's take a little closer look at a switch used with automatic trans-
missions. When the transmission is in low gear or the vehicle speed is
below 35 MPH, the switch is closed, completing the ground circuit; how-
ever, when the vehicle exceeds 35 MPH, the switch opens, breaking the
ground circuit, de-energizing the vacuum solenoid valve (Figure 4-80).
This opening and closing of the automatic transmission switch is regulated
92
-------
SOLENOID VACUUM
SWITCH
CARBURETOR
TRANSMISSION
SWITCH
IGNITION
FIGURE 4-79
AUTOMATIC TRANSMISSIONS
CLOSED OPEN
BELOW 35 MPH
OR LOWER GEARS
ABOVE 35 MPH
OR HIGH GEAR
FIGURE 4-80
by hydraulic pressure in the transmission. The switch may be connected
in the governor circuit, or to the direct clutch of the automatic
transmission, depending upon the type of transmission.
93
-------
The manual transmission switch basically performs the same function. It
is closed in low gears, thus completing the ground circuit to the vacuum
solenoid valve (Figure 4-81) and in high gear, the manual transmission
MANUAL TRANSMISSIONS
CLOSED OPEN
LOW GEARS
HIGH GEAR
FIGURE 4-81
switch is open. This de-energizes the vacuum solenoid valve by breaking
the ground circuit. This opening and closing of the manual transmission
switch is performed by the gear shift linkage.
During the time vacuum is being denied to the advance unit on the
distributor, the vacuum trapped between the vacuum solenoid valve and
the vacuum advance unit on the distributor is purged with atmospheric
pressure. This is done through a vent opening on the vacuum solenoid
valve, as illustrated in Figure 4-82. The vent opening usually has a
sponge filter to prevent foreign particles from entering the vacuum
solenoid valve. The trapped vacuum, between the solenoid valve and the
advance unit, must be released to allow the advance unit to return to
vacuum off position.
To improve cold engine driveability, a CTO (cold temperature override)
switch has been installed in the transmission control spark system
(Figure 4-83). The purpose of this switch is to allow manifold vacuum
94
-------
NO SPARK ADVANCE
FIGURE 4-82
CTO
SWITCH
COOLANT
TEMPERATURE
OVERRIDE
SWITCH
FIGURE 4-83
to the advance unit on the distributor when the engine coolant tempera-
ture is below approximately 160 F (71.1 C). This CTO switch is a tempera-
ture sensitive vacuum switch that allows the vacuum to be controlled
according to the engine coolant temperature.
95
-------
At cool temperatures, the CTO switch prevents carburetor ported vacuum, at
the lower port, from reaching the center port which is connected to the
distributor vacuum control unit. The upper port is open to the center
port which is connected to the distributor vacuum control unit. This
allows full manifold vacuum to the vacuum advance unit on the distributor
when the engine coolant temperature is below approximately 160°F (Figure
4-84). This improves driveability during the warm-up periods.
TO IGNITION
SWITCH
OPEN OVER
35 MPH
^ OR HIGH GEARS
FIGURE 4-84
When coolant temperature rises, the expansion of the material in the
lower chamber of the switch pushes up on the ball, blocking off manifold
vacuum from the top port and allowing ported vacuum from the bottom port
to enter the center port. This center port is connected to the vacuum
advance unit on the distributor. This is the position of the CTO switch
under normal operating conditions (Figure 4-85).
Proper routing of vacuum hoses is very important because they help
determine the proper operation of the transmission control spark system.
Figure 4-86 shows the proper routing of vacuum hoses. On the CTO (cold
temperature override) switch, port 1, the upper port is connected to
intake manifold vacuum. Port D, which controls the device, is connected
96
-------
ABOVE I60°F
TO IGNITION
SWITCH
OPEN OVER
35 MPH
^ OR HIGH GEARS
FIGURE 4-85
TO IGNITION
SWITCH
FIGURE 4-86
to the vacuum advance unit on the distributor and the lower port, port 2,
is connected to carburetor ported vacuum. The cold temperature override
switch is usually mounted very close to the thermostat housing to sense
the highest coolant temperature.
97
-------
Let's review the transmission control spark. The vacuum solenoid valve
is connected between port 2 of the CTO switch and the carburetor ported
vacuum. From the terminal leads of the vacuum solenoid valve we have
connected the transmission switch and the ignition switch. Port D of the
CTO switch is connected to the distributor and port 1 to the manifold
vacuum. If temperatures are below 160°F (71.1°C), the ball in the CTO
switch will be in a lower position, thus blocking off any vacuum that
might be coming from carburetor ported vacuum (Figure 4-87). If the
the automobile is running between 0 and 35 MPH or in lower gears, the
0°-I60°F
TO IGNITION
SWITCH
CLOSED UNDER
35 MPH
*• OR HIGH GEARS
FIGURE 4-87
transmission switch is closed, thus completing the ground circuit and
energizing the vacuum solenoid valve. The vacuum solenoid valve being
energized will then block vacuum from the carburetor going to the CTO
switch.
Remember, there is a vent (Figure 4-88) in the vacuum solenoid valve
to allow atmospheric pressure to purge any vacuum remaining between
the vacuum solenoid valve and the vacuum advance unit on the distributor.
98
-------
TO IGNITION
SWITCH
CLOSED UNDER
35 MPH
OR HIGH GEARS
FIGURE 4-5
Some transmission control spark systems are equipped with a hot over-
ride swtich (Figure 4-89). The purpose of this hot override switch is
to provide full manifold vacuum to the advance unit on the distributor
when coolant temperatures reach 225°F (107.2°C). This advances the
spark, resulting in a faster idle for more efficient cooling.
HOT-COOLANT OVERRIDE SWITCH
I/CARBURETOR
VACUUM
^DISTRIBUTOR
/ADVANCE
PORT
!-MANIFOLD
VACUUM
COOLANT
TEMPERATURE
SENSOR
FIGURE 4-89
99
-------
The hot override switch (Figure 4-90) is basically constructed the same
as the CTO switch just discussed. However, the hot override switch has
intake manifold vacuum routed to the lower port, port 2. Carburetor
HOT-COOLANT OVERRIDE SWITCH
CARBURETOR
VACUUM
DISTRIBUTOR
ADVANCE
PORT
n> MANIFOLD
J VACUUM
COOLANT
TEMPERATURE
SENSOR
FIGURE 4-90
ported vacuum is connected to the upper port, port 1. The middle port,
or port D, is connected to the lower port of the CTO switch. Let's take
a closer look at the vacuum routings and see what happens as the engine
coolant temperature goes from 0°F (-17.8°C) to 225°F (107.2°C).
With the engine coolant above 160°F, the ball of the CTO switch moves
upward, blocking off any intake manifold vacuum at the top port. When
engine coolant is between approximately 160°F (71.1°C) and 225°F (107.2°C)
(Figure 4-91) ported vacuum is routed to the hot override switch top
port and out port D to the lower port on the CTO switch. Ported vacuum
is now available at port D on the CTO switch which is connected to the
vacuum advance unit on the distributor.
When the coolant temperature is above 225°F (107.2°C) (Figure 4-92)
the ball in the hot override switch moves upward to block off the top
port. This upward movement opens a passage and allows manifold vacuum
100
-------
BELOW 225°F- ABOVE I60°F
PORTED
VACUUM
-CTO
HOT OVERRIDE
PORTED
VACUUM
FIGURE 4-91
ABOVE 225°F
PORTED
VACUUM
CTO
HOT OVERRIDE
MANIFOLD
VACUUM
FIGURE 4-92
to pass through the hot override switch and CTO switch to the vacuum
advance unit on the distributor. With full manifold vacuum being applied
to the vacuum advance unit on the distributor, engine RPM will increase.
The increase in engine RPM allows the fan to draw more air through the
radiator, as well as increase coolant flow. This will reduce coolant
temperature to safe operating levels.
101
-------
Figure 4-93 shows a transmission control spark system equipped with a hot
temperature override switch and a cold temperature override switch. The
vacuum solenoid valve is installed in the vacuum line between carburetor
ported vacuum and the upper port of the hot override switch.
PORTED
VACUUM
-CTO
HOT OVERRIDE
PORTED
VACUUM
FIGURE 4-93
General Motor's thermal vacuum switch (Figure 4-94) operates the same as
the hot override switch, except the internal structure is a little differ-
ent. They use a small piston with seals instead of the ball. Also the
G.M. THERMAL VACUUM VALVE
HOT OVERRIDE NORMAL ADVANCE
POSITION POSITION
D-TO DIS-
TRIBUTOR ™y
C-TO PORTED L
VACUUM
MT-TO INTAKE
MANIFOLD
FIGURE 4-94
102
-------
internal routing is slightly different. Port D, or the upper port, is
connected to the distributor and the lower port, MT, is connected to
intake manifold and the center port, port C, is connected to the carbure-
tor ported vacuum. Even though most transmissions that control spark
systems are alike, it is important to check the manufacturer's specifica-
tions and service manuals for each specific engine you are working on.
Dual diaphragm distributors (Figure 4-95) are also used as a means to
retard the spark during deceleration and idle. This vacuum unit has a
movable advance diaphragm as shown, which allows the spark to be retarded
DUAL DIAPHRAGM VACUUM ADVANCE
CARBURETOR
VACUUM
CONNECTION
VACUUM
ADVANCE
SPRING
MANIFOLD
VACUUM
CONNECTION
SECONDARY
DIAPHRAGM
PRIMARY
DIAPHRAGM
TO
DISTRIBUTOR
ADVANCE
o=
=^>
RETARD
FIGURE 4-95
at idle and advance normally at part throttle. Two chambers are used
along with two calibrated springs which allow the ported vacuum signal
to overcome manifold vacuum under part throttle conditions.
103
-------
On some engines, advanced spark timing is required during periods of
deceleration for the purpose of preventing backfiring or popping noise
in the engine exhaust system. The distributor advance control or
deceleration valve shown in Figure 4-96 is added to the advance diaphragm
vacuum supply line for the specific purpose of advancing spark timing
during engine deceleration.
TO MANIFOLD VACUUM
TO
CARBURETOR
(ABOVE
THROTTLE
PLATE)
TO DISTRIBUTOR
FIGURE 4-96
Remember - the purpose of the spark control timing system is to control
the advance and retard of the spark to improve combustion and reduce the
formation of NO and the HC emissions.
X
104
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CATALYTIC CONVERTER SYSTEM
DVCS CTVS
SCS OSAC
ESC PVS
DVB EFE
BPS TRSH
CEC FE
CAP
CTO DR
CCS ECS
CAM VT
RDV VHC
IEDM DSC
CEGR PCV
TAV EGR
AIR TCS
AV TAG
VS TRS
:CSA TIC
Al ISS
AT VAS
DV EES
VA EAC
PV CAI
•AS DTVSy
FIGURE 4-97
The purpose of emissions control systems is to reduce the amounts of HC,
CO and NO that are discharged to atmosphere from the automobile (Figure
A
4-97). Some of these devices control spark timing for more complete com-
bustion; others prevent the escape of fumes and vapors and re-introduce
these for further combustion. Other modifications control the air/fuel
ratio so extra oxygen is available for more complete combustion. Let's
see how the catalytic converter fits into the automotive emissions control
program.
The automobile manufacturers found that a device called the catalytic
converter would reduce HC and CO emissions to a value that would meet
EPA requirements for 1975 and 1976. The catalytic converter would also
allow engines to be retuned for more power, performance and better fuel
economy.
Catalytic converter systems reduce the amount of hydrocarbons (HC) and
carbon monoxide (CO) in the automobile exhaust by providing an additional
area for oxidation or burning to occur as shown in Figure 4-98.
105
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FIGURE 4-98
The catalytic converter looks like another muffler. It is located on the
automobile exhaust system ahead of the muffler and fairly close to the
exhaust manifold (Figure 4-99).
SINGLE EXHAUST SYSTEM
WITH CATALYTIC CONVERTER
MUFFLER
EXHAUST
CATALYTIC
CONVERTER
FIGURE 4-99
On vehicles with one exhaust pipe, one catalytic converter is used. If
the vehicle has dual exhausts, two catalytic converters will normally be
used (Figure 4-100).
106
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DUAL EXHAUST SYSTEM
WITH CATALYTIC CONVERTER
EXHAUST
PIPE
ASSEMBLY
CATALYTIC
CONVERTERS
FIGURE 4-100
Looking closer at the catalytic converter, one difference can be seen
that distinguishes it from an ordinary muffler (Figure4-101). That
difference is that the shell or outer skin of the converter is made of
stainless steel. Stainless steel is more durable and corrosion resistant
than the metal used in ordinary muffler construction.
CATALYTIC CONVERTER
MUFFLER
FIGURE 4-101
107
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There are two basic internal designs for catalytic converters: a monolith
design and a pellet design.
As exhaust gases enter a monolith type catalytic converter (Figure 4-102)
they first encounter a flow diffuser. The flow diffuser spreads or
diffuses the exhaust gases for a more even flow through the next component
MONOLITH CONVERTER
FLOW DIFFUSER
EXHAUST
GASES
HONEYCOMB
MONOLITH
STAINLESS STEEL
SHELL
STAINLESS
STEEL MESH
FIGURE 4-102
which is the monolith catalytic converter element. Surrounding the mono-
lith converter element is a stainless steel mesh. The purpose of this
mesh is to cradle the monolith element and protect it from road shock.
The monolith element is a honeycomb type design (Figure 4-103). The
element has hundreds of cellular passages for the exhaust gases to flow
through. The element is made of a ceramic material. A very thin coating
of platinum and palladium is used to cover this cellular ceramic element.
The pellet style of catalytic converter (Figure 4-104)works in the same
manner as the monolith converter. Rather than a ceramic monolith element,
the pellet style converter uses small aluminum oxide pellets approximately
1/8" to 3/16" in diameter. These small aluminum oxide pellets are coated
with a very thin layer of platinum and palladium.
108
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MONOLITH CONVERTER
EXHAUST
GASES
COATING OF
PLATINUM AND
PALLADIUM
FIGURE 4-103
PELLET - STYLE
CATALYTIC CONVERTER
INSULATION
INSULATION
ALUMINUM OXIDE PELLETS
FIGURE 4-104
The exhaust gases enter the pellet converter (Figure4-105) and are directed
upward by baffles. The only way for the exhaust gases to leave the
converter is to flow downward, passing through the bed of pellets and
then out of the converter to the muffler. The pellet bed is supported
by baffle plates. There is also a layer of insulation that enclosed the
baffles and pellet bed.
109
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EXHAUST GAS FLOW-THRU
PELLET-STYLE CATALYTIC
CONVERTER
INSULATION
EXHAUST /
GASES
INSULATION
ALUMINUM OXIDE PELLETS COATED
WITH PLATINUM AND PALLADIUM
FIGURE 4-105
Both types of catalytic converters perform efficiently but both have
advantages and disadvantages. The monolithic converter is more resistant
to damage from vibration and is physically smaller. Therefore, it heats
up faster allowing it to perform its function sooner. The monolithic
converter offers less resistantce to exhaust flow and therefore has less
back pressure. The disadvantages of the monolithic types are: they are
not repairable; they must be replaced; they are more expensive to build;
and they require more platinum.
The pellet type converter design is repairable; the pellets can be
replaced; it uses less platinum and therefore, is less expensive to
build. The disadvantages of the pellet converter design are: they warm
up slower because of their larger size; they offer more resistance to
exhaust gas flow; and they are not quite as durable as the monolith design,
Platinum and palladium, used in both converters, are noble metals. These
elements are used as the catalytic agents of the catalysts. Both types
of converters use approximately 70% platinum and 30% palladium. Platinum
is the better of the two as a catalyst, but is very expensive. Palladium
is not as efficient as platinum, but is used to reduce the overall cost.
110
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A catalyst is a substance used to speed up a chemical reaction. The
nice thing about a catalyst is, it does not change chemically, nor is
it used up. (Platinum and palladium are used in the oxidizing catalytic
converter which reduces hydrocarbons and carbon monoxide).
The purpose of oxidizing catalytic converter is to oxidize or add
oxygen to certain harmful elements and compounds in the exhaust gas.
These harmful elements and compounds are oxidized to harmless compounds.
In automotive applications, the chemical compounds that require oxidizing
are hydrocarbons (HC) and carbon monoxide (CO) as shown in Figure 4-106.
The hydrocarbons (HC) are portions of unburned fuel. The carbon monoxide
(CO) results when there is insufficient oxygen to completely oxidize
carbon (C) atoms to carbon dioxide (C0?).
THESE DANGEROUS COMPOUNDS
IN THE EXHAUST CAN BE
OXIDIZED INTO
HARMLESS
COMPOUNDS
BY THE
CONVERTER
FIGURE 4-106
In the catalytic converter, oxidizing or burning takes place. The
temperature of this secondary combustion is approximately 200°F (93.3°C)
higher than the temperature of the exhaust gases entering the converter.
If the exhaust gas is 1200°F (648°C) when it enters the converter, it
111
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will begin to burn or oxidize and raise the temperature to approximately
1400°F (760°C) in the converter (Figure 4-107).
SECONDARY COMBUSTION OR
BURNING OCCURS IN THE
CATALYTIC CONVERTER
MUFFLER
FIGURE 4-107
Additional air is supplied to the catalytic converter (Figure 4-108) for
the burning or oxidizing process by two means: an AIR pump, which pumps
ADDITIONAL AIR IS SUPPLIED TO
THE CATALYTIC CONVERTER BY=
AIR INJECTION SYSTEMS
LEAN AIR-FUEL RATIOS
FIGURE 4-108
112
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air into the exhaust manifold, and excessive air in the exhaust manifold
that has not been used in the combustion process.
During the oxidizing or burning in the catalytic converter the hydro-
carbons are broken into hydrogen (H) and carbon (C) atoms. The hydrogen
(H) is then oxidized and converted to water vapor (FLO). The carbon (C)
is also oxidized and converted to carbon dioxide (002)- Any carbon mon-
oxide (CO) resulting from incomplete combustion is also oxidized to
carbon dioxide (C0?). Both water vapor (hLO) and carbon dioxide (CCL)
are harmless gases and do not pollute the air (Figure 4-109).
HC AND CO ARE OXIDIZED IN
THE CATALYTIC CONVERTER
TO H20 AND C02
FIGURE 4-109
The oxidizing catalytic converter begins working when exhaust gas tempera^
tures reach approximately 500 F (260 C). As the vehicle is being driven,
the normal operating temperatures inside the converter will be 1200°F
(648.9°C) to 1600°F (871.1°C) as shown in Figure 4-110. During these
operating conditions, the outside stainless steel shell temperatures
will be approximately 600-800°F (315.6-426.7°C).
113
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CONVERTER OPERATING
TEMPERATURES
INSIDE
TEMPERATURE
1200-1600° F
SHELL TEMPERATURES 600-800°F
FIGURE 4-110
Much higher temperatures can occur in the converter. These higher temper-
atures can be caused by one or more spark plugs misfiring or a carburetor
malfunction that allows an excessively rich mixture (Figure 4-111). If
either of these conditions occur, an increased burning or oxidation will
occur. This increase in oxidation rate will lead to a rapid increase in
temperature. If this temperature reaches approximately 2500°F (1371.1°C),
the aluminum oxide pellets or the aluminum substrate in the monolith
EXCESSIVELY RICH MIXTURES
CAN LEAD TO A DESTROYED
CATALYTIC CONVERTER
FIGURE 4-111
114
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converter will be damaged to the extent that the converter will have to
be replaced. For this reason, vehicles equipped with catalytic conver-
ters should not be run with spark plug wires that are open, disconnected
or shorted out. If shorting or disconnecting of a spark plug is required,
the engine should not be run for over 30 seconds. Any condition which
allows an excessively rich air/fuel mixture to reach the catalytic con-
verter should be corrected immediately to prevent possible converter
damage.
Some automobile manufacturers have incorporated methods of protecting
the catalytic converter. Figure 4-112 shows a protection system used by
CATALYST PROTECTION SYSTEM
BALLAST RESISTOR .IGNITION SWITCH
TO
BATTERY
START
'RUN
ELECTRONIC
CONTROL UNIT
ELECTRONIC
SPEED
SWITCH
THROTTLE
POSITION
SOLENOID
* BATTERY
FIGURE 4-112
Chrysler Corporation. The purpose of this system is to protect the cat-
alytic converter from overheating and damage during periods of decelera-
tion. When engine speed exceeds 200 RPM, the throttle position solenoid
is energized by a signal from the electronic speed switch. When the
throttle is released, the throttle position solenoid holds the throttle
at a preset point corresponding to 1500 RPM. The electronic speed
switch senses when engine speed drops below 2000 RPM and de-energizes
115
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the throttle position solenoid allowing the throttle plates to return to
the curb idle position. By keeping the throttle plates at a 1500 RPM
position, enough air is admitted during deceleration to allow more com-
plete combustion and prevent excessive hydrocarbon buildup on the con-
verter.
Shown in Figure 4-113 is Ford's Thermactor system that is used to pump
additional air into the exhaust manifold. This additional air permits
CATALYST PROTECTION SYSTEM
SOLENOID
VACUUM
VALVE
TEMPERATURE
SWITCH
CHECK VALVE
PVS ELECTRIC
SWITCH
VACUUM DIFFERENTIAL
VALVE (VDV)
AIR BY-PASS VALVE
AIR PUMP
FIGURE 4-113
further oxidation or burning to occur in the exhaust manifold and also
provides the necessary air for the proper operation of the catalytic
converter.
116
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Some manufacturers use heat shields (Figure 4-114)to protect undercarriage
components from the catalytic converter's additional heat. Vehicles
intended for heavy duty operation, such as trailer towing, will also have
special insulation beneath the carpeting to minimize heat buildup inside
the vehicle.
HEAT SHIELDS
INTERIOR
INSULATING
PADS
HEAT
SHIELDS
CATALYTIC
CONVERTER
LOWER SHIELD
FIGURE 4-114
Any vehicle using a catalytic converter must use lead-free fuel. If
leaded gasoline is used, the lead will coat the platinum-palladium
catalyst material. This coating of lead destroys the effectiveness of
the catalytic converter, requiring it to be replaced or recharged
(Figure 4-115).
Figure 4-116shows the special fuel tank filler neck found on all catalytic
converter equipped cars. A special smaller diameter, unleaded fuel
nozzle must be used to fill the fuel tank. This small diameter fuel
nozzle is the only nozzle that will fit in the new small diameter filler
neck. A spring loaded door inside the filler neck prevents adding fuel
by any other means except this small diameter unleaded fuel nozzle.
117
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LEADED FUEL DESTROYS
CATALYST EFFECTIVENESS
FIGURE 4-115
UNLEADED FUEL FILLER INLET
UNLEADED
FUEL
NOZZLE
LEADED FUEL
NOZZLE
RESTRICTOR
UNLEADED
FUEL FILLER
FIGURE 4-116
One problem associated with catalytic converters is the production of a
sulfuric acid (H2$04) mist (Figure 4-117). Under certain operating
conditions, the oxidizing atmosphere of the converter enhances the produc-
tion of sulfuric acid. Sulfur is normally found in gasoline in very small
quantities. The sulfur (S) is converted to sulfur dioxide (SOp) in the
118
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UNDER CERTAIN OPERATING
CONDITIONS A SULFURIC ACID
(H2S04) MIST CAN BE PRODUCED
H2S04
C02
2 S02 + 02
S03 + H20
2S03
H2S04
FIGURE 4-117
combustion process. When the sulfur dioxide (S02) reaches the converter,
it is further oxidized to sulfur trioxide (SO.,). Under certain conditions
the sulfur trioxide will combine with water vapor (H^O) and form sulfuric
acid (H2S04) mist.
Oxidizing catalytic converters used to control hydrocarbons and carbon
monoxide, cannot control oxides of nitrogen (NOV). NO is formed in the
X X
combustion chamber where an oxidizing atmosphere converts nitrogen (N)
to nitric oxide (NO) and nitrogen dioxide (N09). In order to control NO
L- X
emissions from automobiles, a reducing catalyst would be needed. A
reducing catalyst would reduce or change chemical compounds that have
been oxidized back to their unoxidized condition. A reducing catalyst
will convert NO and N02 back to nitrogen (N) and oxygen (0^) both of
which are harmless (Figure 4-118).
Remember - the purpose of the catalytic converter system is to reduce
exhaust emissions by oxidizing hydrocarbons and carbon monoxide into
harmless gases.
119
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OXIDIZING
CONVERTERS
OXIDIZE
HC + CO
H + 02— H20
C + Q.— CQ.
REDUCING
CONVERTERS
REDUCE NO
2NO—
vmn m) nnnjmTTTT
FIGURE 4-118
120
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