EPA-450/3-77-040
November 1977
MOTOR VEHICLE
EMISSIONS CONTROL
BOOK FIVE
EXHAUST GAS
RECIRCULATION SYSTEMS
: ••.'••"••.•"»;•••.*;.•
•'-•'. •'\/':''^
- ••'•': •
.•«..•:
* I • •
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 2771 1
-------
EPA-450/3-77-040
MOTOR VEHICLE EMISSIONS CONTROL
BOOK FIVE
EXHAUST GAS
RECIRCULATION SYSTEMS
by
B.D. Hayes, Project Director
M.T. Maness, Associate Project Director
R.A. Ragazzi, Principal Investigator
R.A. Barrett, Graduate Research Assistant
Department of Industrial Sciences
Colorado State University
Fort Collins, Colorado 80523
EPA Grants No. T008135-01-0 and T900621-01-0
EPA Region VIII Project Officer: Elmer M. Chenault
EPA Project Officer: Bruce Hogarth
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Control Programs Development Division
Research Triangle Park, North Carolina 27711
November 1977
-------
Copies of this publication are available free of charge to Federal employees,
current contractors and grantees, and nonprofit organizations - as supplies
permit - from the Library Services Office (MD-35), Environmental Protection
Agency, Research Triangle Park, North Carolina 27711; or, for a fee, from
the National Technical Information Service, 5285 Port Royal Road, Springfield,
Virginia 22161.
This report was furnished to the Environmental Protection Agency by the
Department of Industrial Sciences, Colorado State University, Fort Collins,
Colorado, 80523, through Grants No. T008135-01-0 and No. T900621-01-0.
The contents of this report are reproduced herein as received from Colorado
State University. The opinions, findings, and conclusions expressed are
those of the authors and not necessarily those of the Environmental Protection
Agency. Mention of company or product names is not to be considered as
an endorsement by the Environmental Protection Agency.
Publication No. EPA-450/3-77-040
ii
-------
MOTOR VEHICLE EMISSIONS CONTROL
- SERIES OF SEVEN BOOKS --
MOTOR VEHICLE EMISSIONS STAFF, COLORADO STATE UNIVERSITY
BOOK ONE - POSITIVE CRANKCASE VENTILATION SYSTEMS
BOOK TWO - THERMOSTAT 1C AIR CLEANER SYSTEMS
BOOK THREE - AIR INJECTION REACTION SYSTEMS
BOOK FOUR - FUEL EVAPORATION CONTROL SYSTEMS
BOOK FIVE - EXHAUST GAS RECIRCULATION SYSTEMS
BOOK SIX ~ SPARK CONTROL SYSTEMS
BOOK SEVEN - CATALYTIC CONVERTER SYSTEMS
iii
-------
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, and Region VIII
Environmental Protection Agency, Manpower Development
Division.
A special thanks must be extended to the automotive vehicle
equipment and parts manufacturers for their cooperation and
assistance in the development of this training material.
iv
-------
INSTRUCTIONS FOR THE USE OF THIS BOOK
This book is one of a series designed specifically to teach the concepts
of automobile emissions control systems. Each book is designed to be
used as self-instructional material. Therefore, it is important that
you follow the step-by-step procedure format so that you may realize the
full value of the emissions system which is being presented. The topics
are taught in incremental steps and each topic treatment prepares the
student for the next topic. Each book is divided into sections which
include the introduction, purpose, function, inspection and testing of
the emissions system presented.
As you proceed through this series, please begin with book one and read
the following books in sequence. This is important because there are
several instances where material covered in a given book relies on
previously covered material in another book.
To receive the full benefits of the book, please answer the self-
evaluation statements related to the material. These statements are
separated from the text by solid lines crossing the page. The answers
to the statement can be found at the end of the book as identified by
the table of contents. You should check for the correct answer after
you respond to each statement. If you find that you have made a mistake,
go back through the material which relates to the statement or statements.
Fill-in-the-blank statements are utilized for self-evaluation purposes
throughout the material. An example statement would appear like this:
The American flag is red, white, and
You would write "blue" in the blank and immediately check your answer at
the end of the book.
v
-------
The material, statements and illustrations should be easy to follow and
understand. In several illustrations a small ghost named "VEC" (Vehicle
Emissions Control) has been used to make the picture easier to understand.
Upon completion of this series, you should be able to better understand
the emissions control systems and devices which are an integral part of
automobiles today. Your increased knowledge should help you keep these
"emissions controlled" vehicles operating as they were designed to
operate. Respectable fuel economy, performance and driveability, as well
as cleaner air, can be obtained from the automobile engine that has all
of its emissions systems functioning properly.
vi
-------
CONTENTS
Introduction to Emissions Control 5-1
Hydrocarbons 5-1
Carbon Monoxide 5-1
Oxides of Nitrogen 5-2
Formation of Hydrocarbons 5-2
Formation of Carbon Monoxide 5-3
Formation of Oxides of Nitrogen 5-3
Ignition Timing 5-3
Carburetion 5-5
System Introduction 5-7
System/Component Purpose 5-13
The EGR Valve 5-13
Sources of Vacuum 5-14
Coolant Temperature Override Switch 5-17
Ambient Temperature Switch 5-18
Vacuum Amplifier 5-20
Exhaust Back Pressure Sensor 5-21
Vacuum Bias Valve 5-23
EGR Delay Timer 5-24
System/Component Function 5-27
EGR Valve 5-27
Dual Diaphragm EGR Valve 5-30
Ported Vacuum EGR System 5-32
Venturi Vacuum EGR System 5-35
Back Pressure Sensor EGR System 5-37
Floor Jet EGR System 5-40
System Inspection 5-43
System Testing 5-47
Testing the Ported Vacuum EGR System 5-47
Testing the Venturi Vacuum EGR System 5-51
Testing the Back Pressure Sensor EGR System .... 5-53
Summary 5-57
Answers 5-59
vii
-------
INTRODUCTION TO EMISSIONS CONTROL
As we all know emissions systems and devices have been installed on the
automobile engine because of the air pollution problem. In order for
you to understand these emissions systems and devices you should have a
background of the problem. All of the emissions control systems were
installed on the engine to reduce just three specific exhaust products.
These are known as products of combustion. The three products which the
emissions systems are designed to reduce are hydrocarbons, carbon monoxide
and oxides of nitrogen.
HYDROCARBONS
Gasoline, like all petroleum products, is made up of hundreds of hydro-
carbon compounds. The name "hydrocarbon" has been given to these com-
pounds because they are made up of hydrogen and carbon atoms. This is
also the reason hydrocarbons have the abbreviation (HC).
Hydrocarbons are gasoline vapors or raw gasoline itself. One reason
hydrocarbon emissions must be controlled is because it is one of the
major components of photochemical smog. Photochemical or "Los Angeles"
smog forms when hydrocarbons and oxides of nitrogen combine in the
presence of sunlight. In order to avoid this smog condition the hydro-
carbon emissions from automobiles must be controlled. Hydrocarbons
also act as an irritant to our eyes and some are suspected of causing
cancer and other health problems.
CARBON MONOXIDE
Another product of combustion that must be controlled is carbon monoxide.
Carbon monoxide has the abbreviation (CO). CO is also hazardous to our
health when it is mixed with the air we breathe. It can cause headaches,
reduce mental alertness and even cause death if enough of it is in the
air. Carbon monoxide is also a problem in that it speeds the formation
of photochemical smog. For these reasons CO emissions must be controlled.
5-1
-------
5-2
OXIDES OF NITROGEN
Oxides of nitrogen are the last harmful products of combustion we will
discuss. Nitrogen oxides have been given the abbreviation (NO ). As
^
you already know, oxides of nitrogen and hydrocarbons combine to form
photochemical smog. The sunlight which triggers the formation of photo-
chemical smog has another effect on oxides of nitrogen. Some of the
oxides of nitrogen are broken down and a gas called ozone is formed.
Ozone is a lung and eye irritant and it also deteriorates rubber and
affects the growth of vegetation. Since the nitrogen oxides have these
effects they must also be controlled.
Now that you are familiar with the emissions which must be controlled
let's find out where they originate.
FORMATION OF HYDROCARBONS
Hydrocarbons, you will recall, are fuel vapors or raw fuel. For this
reason hydrocarbon emissions will result from any uncontained supply
of gasoline. Hydrocarbon emissions also come from the tailpipe. If
the automobile engine could achieve "complete combustion," all of the
unburned fuel or hydrocarbons would be used up. However, it is impos-
sible for today's automobile engines to achieve "complete combustion."
Any time the fuel mixture in the combustion chamber is not completely
burned, some hydrocarbons will be emitted from the tailpipe. The two
main reasons why hydrocarbons are not completely burned are because of
engine misfire and "quench areas." When an engine misfire occurs, none
of the raw fuel or hydrocarbons are burned. When this happens they are
simply exhausted directly to the atmosphere. Quench areas are places in
the combustion chamber where the flame goes out before the fuel is com-
pletely burned. Small cavities such as where the head gasket seals the
cylinder head to the block is a quench area. Another quench area is
located between the top of the piston and the first compression ring.
These areas are sources of hydrocarbon emissions.
-------
5-3
FORMATION OF CARBON MONOXIDE
Carbon monoxide is partially burned fuel. Carbon monoxide is formed in
the combustion chamber whenever there is not enough air to burn all the
fuel. This means that whenever a "rich" air/fuel mixture is pulled into
the combustion chamber carbon monoxide will be formed. After the flame
goes out the carbon monoxide is exhausted through the tailpipe and into
the air.
FORMATION OF OXIDES OF NITROGEN
Oxides of nitrogen are also formed in the combustion chamber. These
oxides result from the nitrogen which is contained in our air. In some
cases combustion temperatures in the automobile engine can exceed 4500°F.
At temperatures above approximately 2500°F, nitrogen oxides will start
forming. Therefore, if combustion chamber temperatures exceed 2500°F,
oxides of nitrogen will be produced and then exhausted to our atmosphere.
Now that you understand how these emissions are formed in the automobile
engine, we will see how changes in ignition timing and carburetor adjust-
ment affect the amount of these pollutants.
As you know, changes in timing and carburetion can have a large effect
on how an engine performs. These changes in timing and carburetion also
can have drastic effects on the amount of pollutants which are present
in the automobile's exhaust. The amount of hydrocarbons, carbon monoxide
and oxides of nitrogen which are present in the exhaust gases will vary
as timing and carburetion adjustments are changed.
IGNITION TIMING
Prior to emissions controlled automobiles, advancing the spark timing
was a common practice. Setting the spark timing this way caused the
spark plug to fire before the piston reached top dead center. This
advanced spark timing allowed the maximum amount of heat energy to be
-------
5-4
exerted on the piston. As a result the best performance and fuel econ-
omy could be obtained. Unfortunately, this also produces high hydro-
carbon and nitrogen oxide emissions levels.
In order to reduce emissions levels, ignition spark timing was retarded.
By firing the spark plug after the piston reaches top dead center, not
as much of the heat energy is converted to work on the piston. The
extra heat energy which is not used on the piston now passes through
the exhaust valve and into the exhaust manifold. This keeps the exhaust
gas temperatures higher. These higher exhaust temperatures allow burning
of the air/fuel mixture to continue in the exhaust manifold. This further
oxidation or burning in the exhaust manifold helps to reduce HC and CO
emissions.
Another advantage of retarded timing from an emissions standpoint is
that combustion temperatures are not as high. This is due to the fact
that the maximum combustion pressure will be lower. Since the combustion
temperatures will be lower and the formation of oxides of nitrogen de-
pends on temperature, a smaller amount of these pollutants will be ex-
hausted to the atmosphere.
There is one more advantage to using retarded spark timing. As you know,
when ignition timing is retarded the engine's idle speed will drop. This
decrease in idle speed occurs because less heat energy is applied to the
combustion chamber and more heat energy is being supplied to continue the
burning process in the exhaust manifold. In order to regain an acceptable
idle speed, the throttle plates must be opened wider. This wider throttle
plate opening allows more air to pass through the carburetor. This increase
in air flow will reduce the amount of residual exhaust gases in the cylinder.
This in turn will allow a more burnable mixture which can be made leaner.
Since the mixture can be leaner there will be more air in the combustion
chamber. As you know, the more air that is made available during com-
bustion the lower will be the HC and CO emissions.
-------
5-5
CARBURETION
Adjustments made to the carburetor air/fuel ratio can also have a large
effect on the amount of pollutants which come from the automobile engine.
When idle mixture settings become richer there is less air present for
the combustion process. This lack of air results in an increase in hydro-
carbon and carbon monoxide emissions.
When idle mixture screws are turned in, the amount of fuel is reduced
and the mixture becomes leaner. This leaner mixture contains more air
and therefore more oxygen is available for more complete burning of the
fuel. This results in lower HC and CO emissions levels.
As the Idle mixture screws are turned in, the idle air/fuel mixture be-
comes leaner. If this mixture becomes too lean a "lean misfire" will
occur. A "lean misfire" will occur because the fuel is so diluted or
thinned out by the air that the mixture will not ignite. This leads to
a very large increase in hydrocarbon emissions. This happens because
the failure of the mixture to ignite results in that amount of raw fuel
being emitted to the atmosphere.
The carbon monoxide emissions decrease when a lean misfire condition is
present. Carbon monoxide is partially burned fuel. Since no combustion
takes place during a lean misfire condition no CO is formed and the total
amount of CO produced by the engine will be less.
A lean misfire usually occurs in one or more cylinders. This condition
may also move from cylinder to cylinder while the engine is running.
This is caused by the uneven distribution of the air/fuel mixture
delivered to each cylinder. This condition occurs mainly because of
problems with intake manifold design.
Now you should understand how changes in timing and carburetion adjust-
ment can affect emissions levels. With this knowledge you will be able
to understand how each emissions control system we will discuss helps to
reduce the air pollution caused by the automobile.
-------
5-6
BLANK PAGE
-------
EGR
5-7
SYSTEM INTRODUCTION
The next emissions control system we will discuss is the Exhaust Gas
Recirculation System. The Exhaust Gas Recirculation system is abbre-
viated EGR system.
The EGR system provides a way to recirculate, or return into the intake
manifold, a small portion of the exhaust gases. These exhaust gases
are mixed with the fresh, air/fuel mixture. Why mix exhaust gases with
a clean air and fuel mixture? Normally we do not expect to find this
done in an automobile engine.
FIGURE 5-1
Before we go any deeper into the EGR system, let's go back and review,
just a little, on what we know about air and combustion. This review
will help you understand why an exhaust gas recirculation system is used.
As you recall, and as VEC is pointing out in figure 5-2, air is made up
of about 21% oxygen (Op), 78% nitrogen (N2) and 1% of other harmless
gases.
-------
5-8
i i r ( f i i i i i (
AIR
21% = OXYGEN
78% = NITROGEN
1% =OTHER
1 ) J M ) J 1 ) J 1 1 1
FIGURE 5-2
We need the oxygen, to support the burning of the fuel in the combustion
chamber. The nitrogen in the air we normally do not think about. Nitro-
gen is called an inert gas. By inert, we mean that nitrogen is very
stable just the way it is, and does not want to change or combine with
any other elements. Now let's see what happens when we take air, mix
it with fuel and burn it in the combustion chamber. As we have already
mentioned, we use the oxygen in the air to support the burning of the
fuel. The nitrogen in the air behaves differently under the high temper-
atures and pressures of combustion. When the temperature gets above
about 2500°F., nitrogen can no longer be called inert.
Under these high temperatures, nitrogen and oxygen are chemically changed
and combine to form a variety of gases. These gases containing nitrogen
and oxygen are grouped together and given the name oxides of nitrogen or
NO . As you know NO plays a big part in the formation or making of
X A
photochemical smog. To help make our air cleaner and reduce some of this
trouble with nitrogen, we use the EGR system. Before we see how the EGR
system reduces NO , let's review some of the main points previously covered,
A
-------
EGR
5-9
FIGURE 5-3
We know that the exhaust gas is inert. By inert, we mean that nearly
99% of the oxygen and fuel has been burned. If it has been burned once,
it cannot support or aid the burning of the fresh air/fuel mixture in
the cylinder. This recirculated exhaust gas is mixed with the fresh
air/fuel mixture and tends to dilute it or thin it out.
The same is true for the exhaust gas we put in with the fresh air/fuel
mixture. The exhaust gas tends to separate or dilute the air/fuel
mixture and lower the temperature of the burning process. By lowering
the temperature of combustion, less NOV is formed.
X
The EGR system was first used on automobiles in 1972. The only state
which required this system in 1972 was California. However, in 1973,
the EGR system was used on most automobiles sold in the United StatBS.
In 1973 Federal Standards limited the amount of NO that could be emitted
A
from any automobile. This is why the EGR system can be found on almost
all 1973 and newer vehicles.
-------
5-10
1. The EGR system provides a means to recirculate a small
portion of the gases.
2. The EGR system takes the gases and mixes
them with the incoming air/fuel mixture.
3. Under the high temperatures and pressures of combustion
the in the air can no longer be con-
sidered inert.
4. Nitrogen can no longer be called inert when the temper-
ature gets above about .
5. Exhaust gases are gases that have been burned. Since
they have been burned once, they cannot burn again.
For this reason, we call exhaust gases gases,
6. The exhaust gases which are mixed with the fresh air/
fuel mixture tend to dilute the mixture. This dilution
results in a temperature when the air/fuel
mixture burns.
-------
EGR
5-11
7. Less will be formed with lower combustion temper-
atures.
8. EGR is an abbreviation for
-------
5-12
BLANK PAGE
-------
14
EGR
5-13
SYSTEM/COMPONENT PURPOSE
Now you know basically how the EGR system control Is NO emissions. Let's
X
look at the purpose of the EGR system and its components.
The purpose of the EGR system is to recirculate exhaust gases to the in-
take manifold. The amount of exhaust gas recirculated must be carefully
controlled. If too much exhaust gas is supplied at the wrong time, the
engine will run very rough and possibly stall. If the EGR system does
not recirculate enough exhaust gases, NO emissions will not be reduced.
A
For this reason the operation of the EGR valve must be very carefully
controlled.
Let's look at an EGR valve, and some of the different parts or components
that make up some EGR systems. This will show you how the amount of
exhaust gas recirculated is controlled.
THE EGR VALVE
The EGR valve is the center of any EGR system. Its purpose is to regulate
or control the amount of exhaust gas to be recirculated. The EGR valve
CARBURETOR
AIR a FUEL
TO VACUUM SOURCE
EGR VALVE.
FROM EXK SYSTEM
TO INTAKE MANIFOLD
FIGURE 5-4
-------
5-14
is normally bolted to the intake manifold. Directly below the EGR valve
there is an opening that leads to the exhaust system. It is from this
opening that exhaust gas is allowed to pass to the intake manifold. The
only time this exhaust gas is allowed to pass into the intake manifold
is when the EGR valve is opened.
The EGR valve is opened by vacuum. This vacuum may come from different
places on the engine. It would help us later if we took time now to
examine some different sources of vacuum used on today's engines
9. The purpose of the EGR system is to mix exhaust gases
with the air/fuel mixture in the
10. The amount of exhaust gases recirculated to the intake
manifold is carefully controlled by the operation of the
EGR
11. The EGR valve is opened by . When this
valve is open exhaust gases pass to the intake manifold.
SOURCES OF VACUUM
Intake manifold vacuum, as the name suggests, is common to the intake
manifold. This is shown in figure 5-5.
We can consider intake manifold vacuum, to be present from under the
throttle plates in the carbuetor, down through the inside of the intake
manifold and down to the intake valve for each cylinder. This vacuum
-------
EGR
5-15
or lack of pressure is caused by the up and down, or pumping, action of
the pistons. Ported vacuum is another source of vacuum used for the EGR
FIGURE 5-5
system. On a ported vacuum system the tapoff, or point where we get
this vacuum signal, is located above the throttle plates in the carburetor.
PORTED
VACUUM
TAP OFF
POINT
FIGURE 5-6
By locating the tapoff above the throttle plates we can control when the
vacuum signal will occur. At idle the throttle plates are nearly closed.
As you can see in figure 5-6, in this position the throttle plate is below
the tapoff point and no vacuum is present. However, as the throttle begins
-------
5-16
to open, the hole or port for the ported vacuum is uncovered. As the
hole is uncovered it is exposed to the intake manifold vacuum below the
throttle plates. At this time a vacuum is starting to be felt at the
tapoff point. As more of the hole or port is uncovered, the amount of
vacuum increases.
This arrangement allows us to time, or control, when the vacuum signal
will be felt at the EGR valve.
Another source of vacuum used in the control of the EGR valve is venturi
vacuum. As the name says, the venturi vacuum comes from a hole, or tap-
off in the venturi of the carburetor. As you recall, the speed of the
VENTURI
VACUUM
SIGNAL
FIGURE 5-7
air must increase as it passes through the narrow area or venturi section
of the carburetor. This increase in speed causes a low pressure in this
section of the carburetor. This low pressure area, or vacuum is felt at
the tapoff point in the venturi. As engine speed increases, air flow
through the carburetor increases. This increase in air flow means the
speed of the air must also increase. Changes in air speed through the
carburetor depend on the speed or RPM of the engine. These changes in
venturi vacuum result in a vacuum signal that corresponds to engine speed.
At idle, when there is very little air flow, the venturi vacuum would
-------
EGR
5-17
be zero. As engine speed increases the venturi vacuum also increases.
This variable or changing venturi vacuum is used to control some emis-
sions devices.
12. There is vacuum signal at idle with ported vacuum.
13. In a ported vacuum system when the is
uncovered, a vacuum signal is felt as engine speed
increases.
14. vacuum is another source of vacuum used
to control the EGR valve.
15. The venturi vacuum signal would be at idle,
when there is very little air flow through the carbure-
tor.
16. The venturi vacuum signal as engine
speed increases.
COOLANT TEMPERATURE OVERRIDE SWITCH
Another component or part found in many EGR systems is the coolant temper-
ature override switch. This switch is commonly called the CTO switch.
The CTO switch is usually located on the intake manifold. It is threaded
-------
5-18
into-the intake manifold in a location where it can sense the coolant
COOLANT
] TEMPERATURE
OVERRIDE
SWITCH
FIGURE 5-8
temperature of the engine. The CTO switch is located between the source
of vacuum and the EGR valve. It's purpose is to prevent the vacuum signal
from reaching the EGR valve until a certain coolant temperature is reached,
By allowing the engine coolant to warm up before letting the EGR valve
operate, the engine performs much better. This improves cold drive-
ability and engine performance when it is cold.
AMBIENT TEMPERATURE SWITCH
The ambient temperature switch was used on some EGR systems before March
1973. This temperature switch senses the surrounding air temperature
or the ambient temperature. The purpose of the ambient temperature switch
is similar to the CTO switch. That purpose is to control the amount of
vacuum that reaches the EGR valve below a certain temperature. The
ambient temperature switch allows a small amount of air to bleed into
the vacuum line that goes to the EGR valve. This small air bleed reduces
the amount of vacuum that reaches the EGR valve. If less vacuum reaches
the EGR valve, the valve does not open as far. The smaller the opening
of the valve, the less exhaust gas recirculation.
-------
EGR
5-19
AMBIENT TEMPERATURE SWITCH
AIR BLEED
FILTER
TEMPERATURE
SENSING
COVER
FROM
VACUUM SOURCE
FIGURE 5-9
There are two major differences between at CTO switch and an ambient
temperature switch. The first difference is the CTO switch prevents
vacuum from reaching the EGR valve. The ambient temperature switch
allows a small amount of air to bleed into the EGR valve vacuum line.
This air bleed reduces the amount of vacuum that reaches the EGR valve.
The second difference is the CTO switch senses coolant temperature.
The ambient temperatrue switch is located on the engine compartment
firewall and senses ambient air temperature. However, the Environmental
Protection Agency (EPA) said that ambient temperature switches could not
be used. Ambient temperature switches have not been used since March
1973. Since then, the auto makers have used the CTO switch.
17. The
switch is another component found in many EGR systems
-------
5-20
18. The CTO switch is usually threaded into the intake
manifold where it can sense
19. The CTO switch prevents from reaching the
EGR valve until a certain temperature is reached.
20. Some EGR systems manufactured before March 15, 1973
used the temperature switch.
VACUUM AMPLIFIER
The vacuum amplifier is another device used to control the EGR valve.
The name "vacuum amplifier" is misleading. The word "amplifier" means
to make bigger or enlarge. The vacuum amplifier does not make the
vacuum larger. The purpose of the vacuum amplifier is to control the
EGR valve. It uses intake manifold vacuum to control the EGR valve.
But as you know, intake manifold vacuum is high while the engine is
idling. If this high vacuum reaches the EGR valve, it would move the
valve wide open. This would allow too much exhaust gas to be recir-
culated at idle and the engine will idle very roughly and possibly stall.
In order to use intake manifold vacuum to control the EGR valve, it must
be controlled very carefully. This is the job of the vacuum amplifier.
The vacuum amplifier receives a vacuum signal from the carburetor venturi,
This venturi vacuum tells the vacuum amplifier how much intake manifold
vacuum to send to the EGR valve. As you can see the amplifier does not
make the vacuum larger. It merely uses a fairly weak source of vacuum,
-------
EGR
5-21
venturi vacuum, to control or regulate the amount of intake manifold
vacuum going to the EGR valve.
( TO INTAKE MANIFOLE
( TO EGR VALVE ^^
( FROM VENTURI VACUUM SI6NAI^>
FIGURE 5-10
The vacuum amplifier controls the EGR valve. It does this by using a
vacuum signal from the carburetor venturi. As engine speed increases,
the venturi vacuum increases. This signal tells the vacuum amplifier
how much intake manifold vacuum to let reach the EGR valve.
EXHAUST BACK PRESSURE SENSOR
The exhaust back pressure sensor is also found on many EGR systems. It
is sometimes called an exhaust back pressure transducer. As shown in
figure 5-11, there are two basic parts, the sensor and the spacer. The
spacer is located under the EGR valve. In the spacer there is a tube
or line that senses the exhaust back pressure. This line runs from the
spacer to the back pressure sensor. As the name suggests, the back
pressure sensor, senses the pressure in the exhaust system. The sensor
uses this pressure signal to control the amount of vacuum that reaches
the EGR valve. With this device the amount of exhaust gas recirculated
depends on the amount of pressure in the exhaust system. The purpose
of this device is to improve driveability and fuel economy and still
control NO emissions.
n
-------
5-22
EXHAUST BACK-
PRESSURE SENSOR
(TRANSDUCER)
INTAKE PORT
SPACER
CONNECTING
TUBE
EXHAUST PORT
FIGURE 5-11
21. The vacuum amplifier controls the
valve operation.
22. The vacuum amplifier controls the EGR valve by using a
vacuum signal from the carburetor .
23. The venturi vacuum signal increases as engine speed
increases. This venturi signal tells the vacuum
amplifier how much
vacuum to let reach the EGR valve.
-------
EGR
5-23
24. The exhaust back pressure sensor or transducer senses
exhaust
25. The exhaust back pressure signal controls the amount of
that reaches the EGR valve.
26. When operating, the amount of exhaust gas recirculated
depends on the system pressure.
VACUUM BIAS VALVE
The vacuum bias valve is used by only one manufacturer. It is located
between the EGR valve and the vacuum source for the EGR valve. The other
side of the vacuum bias valve is connected to intake manifold vacuum.
VACUUM BIAS VALVE
TO EGR
VALVE
TO MANIFOLD
VACUUM
TO DISTIBUTOR
SPARK-EGR THERMAL
VACUUM VALVE
FIGURE 5-12
-------
5-24
Anytime that a high intake manifold vacuum is present, the amount of
vacuum going to the EGR valve is reduced. This high intake manifold
vacuum condition is present during engine idle. It is also present
during normal highway driving or cruise conditions. During these con-
ditions the amount of exhaust gas recirculated is reduced. This pre-
vents engine surge during these operating conditions. However, during
acceleration, intake manifold vacuum drops. This drop or decrease in
intake manifold vacuum allows more exhaust gas to be recirculated
during this time. The purpose of the vacuum bias valve is to reduce
engine surge. This problem occurs at times when intake manifold vacuum
is high such as engine idle or during highway cruise conditions.
EGR DELAY TIMER
Another method that is used to control the EGR valve is the EGR Delay
Timer. The purpose of this system is to prevent exhaust gas recircula-
tion for a short period of time after the engine is started. The EGR
Delay Timer is made up of two major parts, a vacuum solenoid and the
EGR timer control. The vacuum solenoid is located in the ventrui
vacuum sensing line between the venturi vacuum tapoff point and the
vacuum amplifier. The vacuum solenoid is controlled by the EGR timer
control. The timer control unit is located on the firewall.
VACUUM AMPLIFIER JO INTAKE^
EGR VALVE S7~\ /MANIFOLD
C. VACUUM
CARBURETOR
VENTURI
VACUUM
IGN. 12 V
EGR TIMER CONTROL 4-
VACUUM
SOLENOID
FIGURE 5-13
-------
EGR
5-25
When the ignition key is turned on the vacuum solenoid is energized.
Vacuum is prevented from reaching the vacuum amplifier when the solenoid
is energized. After approximately 35 seconds the EGR timer control de-
energizes the vacuum solenoid. This allows the venturi vacuum to reach
the vacuum amplidier and allow normal EGR operation.
The 35 second delay allows the engine to be started and run for several
seconds before the EGR system begins to operate. This setup allows for
better cold engine operation after initial engine start up.
Now that we have looked at some of the means or devices used to control
and operate the EGR valve, let's put all of this together and look at
some EGR systems. The devices we just talked about will allow us to
examine some complete EGR systems. Me will be able to see how many of
these devices operate to control exactly when the EGR valve will operate
and how the amount of exhaust gas recirculated is controlled.
27. The vacuum bias valve is used to reduce engine
28. Engine surge occurs at times when intake manifold vacuum
is such as engine idle, and during highway
cruise conditions.
29. The purpose of the EGR delay timer is to
exhaust gas recirculation for a short time after the
engine is started.
-------
5-26
30. The EGR delay timer prevents EGR valve operation for
approximately seconds after the ignition key is
turned on.
31. Vacuum is prevented from reaching the vacuum amplifier
by a .
32. The vacuum solenoid is energized and de-energized by the
EGR
-------
EGR
5-27
SYSTEM/COMPONENT FUNCTION
The first component you will look at is the EGR valve. You will look
at the parts that make up an EGR valve and what function these parts
play in the operation of the EGR valve.
EGR VALVE
Figure 5-14 shows a typical EGR valve. The main parts of the EGR valve
are the diaphragm spring, the diaphragm, the pintle or valve and the
pintle or valve seat.
EGR VALVE (CLOSED)
DIAPHRAGM
SPRING ~~^
DIAPHRAGM
PINTLE
SEAT
VACUUM
NIPPLE
PINTLE
FIGURE 5-14
The diaphragm spring pushes down against the diaphragm. This downward
push or force of the spring holds the pintle or valve in its normally
closed position. In the closed position, the pintle or valve rests on
the pintle or valve seat. In this position, no exhaust gas can be
recirculated or mixed with the air/fuel mixture.
The area above the diaphragm, where the diaphragm spring is located, is
a sealed chamber. Coming out of this sealed chamber is a connection for
a vacuum hose.
-------
5-28
As shown in figure 5-15, when vacuum from a vacuum source is allowed to
reach this chamber, the EGR valve begins to open. As the valve or pintle
is lifted off its seat exhaust gases are allowed to flow from the exhaust
passage into the intake manifold. It normally takes between 3 to 5 inches
of vacuum to start opening an EGR valve.
EGR VALVE (OPENS)
DIAPHRAGM
SPRING'
FROM
VACUUM
SOURCE
DIAPHRAG
PINTLE
PINTLE SEAT
FIGURE 5-15
Many EGR valves look very much alike on the outside. Most EGR valves
RESTRICTOR ORIFICE
EGR VALVES
FIGURE 5-16
-------
EGR
5-29
however, are made differently on the inside. If we look at figure 5-16
one of these differences can be seen. The difference between these
valves is in the size of the opening in the bottom of the EGR valve.
This opening or restrictor orifice limits the amount of exhaust gas
that can be recirculated. By changing the size of the restrictor
orifice, the same basic valve can be used for many different engines.
The restrictor orifice size is varied by the manufacturer so it can be
used on a particular engine. So even though the valves look identical
on the outside, be sure to use the correct part number for the car you
are working on. This will insure you are using a valve with the proper
size restriction orifice for that particular engine.
33. The EGR valve is when it is in the normal
position.
34. The EGR valve is held in this closed position by a
35. In this closed position the or pintle is
pushed down against the seat. This prevents exhaust
gas from being recirculated.
36. When the EGR valve is in this closed position, no exhaust
gas can be recirculated or mixed with the
mixture.
-------
5-30
37. The area above the diaphragm, where the diaphragm spring
is located is a chamber.
DUAL DIAPHRAGM EGR VALVE
Another type of EGR valve is the "dual diaphragm" valve shown in figure
5-17. The dual diaphragm EGR valve is recognized by two vacuum hose
DUAL DIAPHRAGM EGR VALVE
jo
CARBURETOR
VACUUM
DUAL
DIAPHRAGMS
INTAKE
MANIFOLD
VACUUM
VALVE
FIGURE 5-17
connections. As you recall, the other EGR valve we have discussed has
only one vacuum hose connection. The dual diaphragm valve, as its name
suggests, has two diaphragms instead of one. The upper chamber has a
connection for carburetor ported vacuum. The lower chamber has a connec-
tion for intake manifold vacuum. Carburetor ported vacuum acts on the
upper diaphragm to open the EGR valve. During high intake manifold con-
ditions with low engine loads, such as highway cruise, intake manifold
vacuum works against ported vacuum. This high intake manifold vacuum
-------
EGR
5-31
pulls the EGR valve towards the closed position. This closing down of
the EGR valve limits the amount of exhaust gas recirculation during
cruise conditions.
During acceleration, intake manifold vacuum drops as the engine load
increases. This drop or decrease in intake manifold vacuum allows the
carburetor ported vacuum to open the EGR valve further. This allows
more exhaust gas recirculation to occur during acceleration. This is
necessary because when the engine loads are greatest, more NO is formed.
38. A dual diaphragm EGR valve can be recognized by
vacuum hose connections.
39. The upper chamber of a dual diaphragm EGR valve has a
connection for ported vacuum.
40. The lower chamber of a dual diaphragm EGR valve has a
connection for vacuum.
41. During high intake manifold conditions (low engine load)
such as highway cruise, intake manifold vacuum works
against vacuum in the dual diaphragm EGR
valve.
42. The dual diaphragm EGR valve allows more exhaust gas
recirculation during .
-------
5-32
43. This extra EGR during acceleration is necessary because
formation is greatest during heavy engine loads.
PORTED VACUUM EGR SYSTEM
The ported vacuum EGR system is made up of three components, the EGR
valve, the coolant temperature override (CTO) switch, and a ported
vacuum tapoff in the carburetor. The ported vacuum tap in the carbu-
retor is located above the carburetor throttle plates.
PORTED VACUUM SYSTEM
LOW COOLANT TEMPERATURE
EGR
CTO
SWITCH
CARBURETOR
EGR VALVE
FIGURE 5-18
As you recall, this port location above the throttle plates only allows
vacuum to the EGR valve when the throttle is opened. Let's look at the
way the ported vacuum system works. We will begin from a cold start
condition. Remember the CTO switch is located in a place where it can
sense the temperature of the engine coolant. When a cold engine is
started the CTO switch prevents vacuum from reaching the EGR valve. In
-------
EXHAUST
GAS
RECIRCULATION
COOLANT
TEMPERATURE
OVERRIDE
SWITCH
EGR
5-33
FIGURE 5-19
the CTO switch a ball valve, shown in figure 5-19, is forced down by a
spring. In this position the ball blocks the path of ported vacuum to
the EGR valve. This prevents the EGR valve from operating when the
throttle is opened.
As the engine coolant temperature increases, the CTO switch senses the
increase in temperature. At a certain temperature the ball valve is
forced upward. The exact temperature varies with the make of car, the
year of the car, and the engine used in that vehicle. As the ball valve
moves upward it opens the path from the carburetor to the EGR valve.
As the throttle is opened, the ported vacuum tap in the carburetor is
uncovered. This allows the ported vacuum to go from the carburetor,
to the now open CTO switch and to the EGR valve. You can see this in
figure 5-20. The vacuum signal can now act on the EGR valve diaphragm
and the EGR valve begins to open, allowing exhaust gas to be recirculated,
With the ported vacuum system, when the throttle plates are wide open,
no exhaust gas recirculation takes place.
-------
5-34
PORTED VACUUM SYSTEM
COOLANT AT
NORMAL OPERATING TEMPERATURE
CARBURETOR
EGR
CTO
SWITCH
FIGURE 5-20
You will recall that it takes between 3 to 5 inches of vacuum to start
opening an EGR valve. During wide open throttle operation intake mani-
fold vacuum will be below this value. So at wide open throttle, the
EGR valve is closed by spring pressure.
44. When coolant temperature is above the specified value,
the in the CTO switch moves up and allows a
path for ported vacuum to reach the EGR valve.
45. A ported vacuum signal will reach the EGR valve when the
throttle is
Now that the ported vacuum system is understood let's look at another
type of system: The venturi vacuum EGR system.
-------
EGR
5-35
VENTURI VACUUM EGR SYSTEM
The venturi vacuum EGR system is made up of four major parts. These
are the EGR valve, a vacuum amplifier, a CTO switch and the venturi
vacuum tap on the carburetor. Let's look at the events that make this
VENTURI VACUUM EGR SYSTEM
CARBURETOR
VENTURI VACUUM LINE
VACUUM
AMPLIFIER'
V
INTAKE MANIFOLD
VACUUM LINE
EGR VALVE
FIGURE 5-21
type of EGR system operate. When the engine is started there is a con-
tinuous flow of air through the carburetor. As the engine is accelerated
this air flow increases. This increase in air flow means the speed of
the air must also increase. As the speed of the air increases, a vacuum
is created in the venturi vacuum signal line that goes to the vacuum
amplifier. The vacuum amplifier also has a manifold vacuum line connected
to it and one other line that goes to the CTO switch. At idle the air
flow and speed are very low and no venturi vacuum signal is sent to the
vacuum amplifier. As engine speed increases a weak venturi vacuum reaches
the vacuum amplifier. This venturi vacuum signal tells the vacuum ampli-
fier how much intake manifold vacuum should be allowed to the CTO switch
and the EGR valve. If the engine coolant temperature is below what the
CTO switch operates at, vacuum is prevented from reaching the EGR valve.
If coolant temperature is above what the CTO switch operates at, vacuum
is allowed to the EGR valve.
-------
5-36
VENTURI VACUUM EGR SYSTEM
VACUUM
AMPLIFIER
VENTURI VACUUM LINE\
\J (( NNTAKE MANIFOLD
VACUUM LINE
EGR VALVE
FIGURE 5-22
When vacuum reaches the EGR valve, it begins to open and allows exhaust
gas recirculation to occur. The venturi vacuum EGR system is similar
to the ported vacuum system in that it does not allow exhaust gas recir-
culation to take place at wide open or full throttle conditions. At
full throttle, there is a large amount of air flowing through the carbure-
tor venturi. This large amount of air is traveling at a very high speed.
This high speed results in a very high venturi vacuum signal. But as
you recall, intake manifold vacuum drops to a very low valve during full
throttle operation. The vacuum amplifier compares the high venturi
vacuum to the low intake manifold vacuum. The vacuum amplifier then
limits intake manifold vacuum to the EGR valve. Intake manifold vacuum
is limited to a value less than the amount of vacuum needed to open the
EGR valve. This prevents exhaust gas recirculation during wide open
throttle.
46. The venturi vacuum signal tells the vacuum amplifier how
much vacuum to apply to the
EGR valve.
-------
EGR
5-37
The next EGR system we will look at will be a ported vacuum system with
a back pressure sensor.
BACK PRESSURE SENSOR EGR SYSTEM
The ported vacuum EGR system with an exhaust back pressure sensor has
five major components. These may be seen in figure 5-23. These components
are the EGR valve, a spacer under the EGR valve, an exhaust back pressure
sensor, a CTO switch, and a ported vacuum tapoff on the carburetor.
PORTED VACUUM EGR SYSTEM WITH
BACK PRESSURE SENSOR
EXHAUST BACK PRESSURE
SENSOR
X
EXHAUST PRESSURE
SENSING LINE
VALVE
SPACER
PORTED VACUUM
FIGURE 5-23
Except for the exhaust back pressure sensor, the other parts are similar
to the ported vacuum EGR system. A cutaway view of the back pressure
sensor and spacer is shown in figure 5-24. Exhaust pressure is sensed
from a hole in the adaptor. This pressure signal travels through a tube
to the sensor or transducer. Inside the transducer is a flexible dia-
phragm that exhaust pressure pushes against. If exhaust pressure is not
strong enough to overcome the spring that is pushing down on the diaphragm,
the air bleed hole remains open. The air bleed hole allows air to be
drawn into the vacuum line when the diaphragm is in the lower position.
An air filter is used in the sensor. This filter removes dirt and dust
from the air that is being drawn into the vacuum line. Let's look at
-------
5-38
ENGINE IDLING
BACK PRESSURE
SENSOR
EXHAUST BACK
PRESSURE
SENSING TU
L EXHAUST BACK PRESSURE
2. SENSOR AIR BLEED OPEN
(AIR DRAWN REDUCES VACUUM)
3. NO PORTED VACUUM SIGNAL
4. E6R VALVE CLOSED
FIGURE 5-24
the operation of this system during idle or low speed (light load) condi-
tions. As shown in figure 5-24, exhaust system back pressure is sensed
from a hole drilled in the spacer under the EGR valve. The exhaust system
pressure signal travels through a hollow tube to the pressure sensor or
transducer. At idle or during a light load condition exhaust back pressure
is low. The exhaust signal at the back pressure sensor is also low. This
signal is too low to overcome the spring pressure that is pushing down on
the sensor diaphragm. This is shown in figure 5-24. With the diaphragm
being pushed down by the spring the air bleed hole is open. This allows
air to bleed into the vacuum line going to the EGR valve. The air being
bled into the vacuum line reduces the vacuum going to the EGR valve. The
reduced vacuum is not strong enough to overcome the EGR valve spring
pressure and the EGR valve is held shut. No exhaust gas recirculation
occurs.
As the load on the engine is increased, such as during part throttle accel-
eration, exhaust back pressure increases. This increase in exhaust back
-------
EGR
5-39
pressure is felt on the bottom of the back pressure sensor diaphragm.
This condition is shown in figure 5-25. The increased exhaust pressure
overcomes spring tension and pushes the diaphragm up. This upward move-
ment of the diaphragm closes off the air bleed hole. With the air bleed
hole closed off, no air can enter the vacuum line to the EGR valve. This
condition allows the ported vacuum signal from the carburetor to reach
the EGR valve. Now the vacuum that reaches the EGR valve is strong
enough to overcome the EGR valve spring and open the valve. Exhaust
gas recirculation now takes place.
ACCELERATION
AIR BLEED PORT
if TEXHAU:
ST GAS
TO INTAKE
MANIFOLD
I. EXHAUST BACK
HIGH
2. SENSOR AIR BLEED CLOSED
3. HIGH PORTED VACUUM SIGNAL
4. EGR VALVE OPEN
PRESSURE
FIGURE 5-25
Under wide open throttle, heavy load conditions, exhaust back pressure
is very high. This high exhaust pressure forces the diaphragm against
the air bleed hole in the back pressure sensor. With the air bleed hole
blocked, no air can enter the vacuum line going to the EGR valve. However,
during full throttle operation intake manifold vacuum and ported vacuum
will be very low. The ported vacuum signal will be so low that the EGR
valve spring will close the EGR valve. There is no exhaust gas recircula-
tion during full throttle with this system as shown in figure 5-26.
-------
5-40
FULL THROTTLE OPERATION
I. EXHAUST BACK PRESSURE HIGH
2. SENSOR AIR BLEED CLOSED
3. LOW PORTED VACUUM SIGNAL
4. EGR VALVE CLOSED
FIGURE 5-26
47. During acceleration, exhaust back pressure is
48. The exhaust gas recirculation system that uses the exhaust
back pressure sensor is very similar to the
EGR system.
FLOOR JET EGR SYSTEM
The last EGR system we will look at is the Floor Jet EGR System. This
system is called the floor jet EGR system because of the location of the
jets. The jets are located in the floor of the intake manifold. See
figure 5-27. These floor jets allow a metered passage for exhaust gases
to flow from the exhaust crossover passage to the intake side of the
-------
EGR
5-41
FLOOR JET EGR SYSTEM
INCOMING
FUEL-AIR ORIFICE
MIXTURE
FLOOR JET
•. •. *jj*s« * • * ^^
EXHAUST GAS
CROSS-OVER
INTAKE
MANIFOLD
RECIRCULATING
GASES
FIGURE 5-27
manifold. Intake manifold vacuum continually draws exhaust gases into
the intake manifold. With this system exhaust gas recirculation occurs
during idle, cruise and wide open throttle conditions. This system was
used by one manufacturer and only for 1973 models.
-------
EGR
5-43
SYSTEM INSPECTION
A visual inspection is important to insure the proper operation of the
EGR system. A visual inspection of hoses and components should be done
periodically. This inspection should take place before any testing of
the system is done. Inspection requires no tools or instruments and
takes only a few minutes. Many problems can be avoided or corrected by
following these steps.
1. Obtain a good technical manual or the manufacturer's
service manual. Use this to locate a vacuum circuit
diagram for the vehicle you are going to inspect.
FIGURE 5-28
There are many different types of EGR systems. These
systems may have different components in them. In
order to do a thorough inspection a good manual should
be used. A good manual will have vacuum circuits in
it. These circuits show what components you can expect
to find on each make and model of car as well as the
components on different engine sizes.
-------
5-44
1. Visually inspect the EGR system. Use the vacuum cir-
cuit diagram to insure all the parts or components
that are required on the vehicle you are inspecting
are installed.
FIGURE 5-29
Each car and engine combination has an EGR system de-
signed for it. This system was designed to keep NO
A
emissions at or below federal standards. In addition
to emissions, the system was designed to insure the
driveability of the car would be acceptable. All
the system components must be installed to insure
the proper operation of the EGR system.
3. Using the vacuum circuit diagram, check for proper
hose routing between the EGR system components.
There are many types of EGR systems; some have up
to five or six components. The proper hook-up or
connection of these components requires many vacuum
hoses. Proper hose routing and the right connections
are very important to the proper operation of the EGR
-------
EGR
5-45
system. The best way to check for the proper routing
of hoses and connections is to use a vacuum circuit
diagram to insure the connections are correct.
4. Inspect all vacuum lines for cracks, loose connections,
or excessive hardness.
Vacuum lines, being located in the engine compartment,
are subjected to a large amount of heat from the engine.
This heat causes these vacuum hoses to become brittle
or hard. When a vacuum hose becomes brittle or hard, it
only takes a small push to crack the hose. This leads
to a vacuum leak that can effect engine performance and
EGR system operation. Each connection should be checked
to make sure the vacuum hose fits snugly. If the hose
does not fit snugly on the connection there is a very
good chance for a vacuum leak to occur. Any vacuum
leak can effect engine performance and cause the EGR
system to operate improperly.
A good visual inspection should only take about ten minutes. This
inspection could show points where trouble might occur and could solve
some problems quickly.
49. Inspection of the EGR system should take place before any
of the system is done.
50. Obtain a good technical manual or the manufacturer's
-------
5-46
51. Using the circuit diagram, check for proper
hose routing between the EGR system components.
-------
EGR
5-47
SYSTEM TESTING
The purpose of testing the EGR system is to insure it is working properly,
EGR systems should be inspected and tested any time the vehicle is being
tuned or when the EGR system is suspected of not operating properly. We
will begin the testing with a ported vacuum EGR system with a CTO switch.
TESTING THE PORTED VACUUM EGR SYSTEM
To test the complete ported vacuum EGR system at one time the following
steps should be followed.
1. Start with a cold engine.
2. Start the engine and slowly increase engine speed to
approximately 2000 RPM.
3. While increasing engine speed watch the stem on the
EGR valve. The EGR valve stem should not move and
the valve should remain closed. If the EGR valve opens
when the engine is cold, the CTO switch is defective
and should be replaced. Remember, the purpose of the
CTO switch is to prevent vacuum from reaching the EGR
valve until the coolant temperature reaches a certain
temperature. The exact temperature the CTO switch should
• .
operate at 'can be found in a technical manual or the
manufacturer's service manual.
4. Allow the engine to warm up to operating temperature.
5. Increase engine speed to approximately 2000 RPM.
6. While increasing engine speed, watch the EGR valve
stem. The EGR valve stem should move in the upward
direction. This test with the warm engine verifies
that the CTO switch did operate and allow vacuum to
reach the EGR valve. If the EGR valve does not open
during this test the following steps should be taken.
7. Disconnect the .vacuum line on the lower connection of
the CTO switch. This vacuum line runs from the ported
vacuum connection on the carburetor to the CTO switch.
-------
5-48
Connect a vacuum gauge to the CTO switch end of the
vacuum line.
8. Increase engine speed to 2000 RPM while watching
the vacuum gauge. If no vacuum reading shows on
the vacuum gauge, the signal ports in the carbure-
tor could be plugged or the vacuum line between
the carburetor and the CTO switch could be plugged.
Determine which is the fault and correct the problem.
EGR VALVE
FIGURE 5-30
if a vacuum reading does show on the gauge, this
verifies that vacuum is available to the CTO switch.
9. Remove the vacuum gauge from the vacuum line and
reinstall the vacuum line on the CTO switch.
10. Remove the vacuum line at the EGR valve and connect
the vacuum gauge to this line.
11. Increase engine speed to 2000 RPM and observe the
vacuum gauge. If reading appears on the vacuum
gauge, this verifies that the CTO switch has opened
and is allowing vacuum to the EGR valve. If no
-------
EGR
5-49
EGR VALVE
FIGURE 5-31
vacuum reading appears on the gauge the CTO switch
is not operating properly and should be replaced.
If the CTO is operating properly and allowing vacuum
to the EGR valve, the following steps should be taken,
EGR
VALVE
FIGURE 5-32
-------
5-50
12. Connect a vacuum hand pump, or an intake manifold vacuum
source, to the EGR valve.
13. Apply 12"-16" of vacuum to the EGR valve.
14. If the EGR valve does not open, it should be replaced.
NOTE: Most manufacturers recommend removing and inspect-
ing the EGR valve at the following intervals.
a. Every 12,000 miles if leaded gasoline is used.
b. Every 25,000 miles if unleaded gasoline is used.
If this maintenance is not performed, carbon and/or lead
deposits build up around the valve seat and valve. These
deposits could prevent the valve from closing completely
or keep it from opening.
The next procedure can be used to check all EGR valves, no matter what
type of system is used to operate them.
1. Start the engine and allow it to come to operating
temperature.
2. Disconnect the vacuum line at the EGR valve.
3. Connect a hand vacuum pump to the EGR valve.
4. Apply vacuum to the EGR valve until it begins to open.
As the EGR valve opens, the engine will begine to idle
roughly and may even stall. If this condition occurs as
the EGR valve is opened and stops when the vacuum is re-
moved from the EGR valve, you can be reasonably sure of
the following:
a. The diaphragm in the EGR valve is not leaking.
b. The EGR valve seats tightly when it is closed.
c. The exhaust passages from the exhaust crossover
on the intake manifold are clear and allowing
exhaust gas recirculation to occur.
If the EGR valve does not open when vacuum is applied
to it, replace the EGR valve.
-------
EGR
5-51
TESTING THE VENTURI VACUUM EGR SYSTEM
The following procedure can be used to test the venturi vacuum EGR
system.
1. Start with a cold engine.
2. Disconnect the venturi vacuum signal hose from the
carburetor.
3. Connect a hand vacuum pump to the venturi vacuum line.
4. Start the engine and apply l"-3" of vacuum to the
venturi vacuum sensing line.
5. Watch the EGR valve stem while applying the vacuum.
The valve stem should not move.
6. Release the l"-3" of vacuum. If the valve begins to
open while the engine is cold the CTO switch is not
operating properly and should be replaced.
TESTING THE
VENTURI VACUUM EGR SYSTEM VACUUM
AMPLIFIER
CTO SWITCH
VENTURI
VACUUM
LINE
INTAKE MANIFOLD
VACUUM LINE
/
EGR VALVE
FIGURE 5-33
7. Allow the engine to come to normal operating temperature.
8. Apply l"-3" of vacuum to the venturi vacuum sensing line.
The EGR valve should begin to open. This can be seen by
watching the EGR valve stem or by a sudden rough idling
-------
5-52
or stalling of the engine. If the EGR valve does not
open, follow these steps.
9. Connect the hand vacuum pump to the EGR valve.
10. Apply 10"-12" of vacuum to the EGR valve.
11. If the valve does not open - replace the EGR valve.
12. If the valve does open, disconnect the vacuum line going
to the bottom connection of the CTO switch and install a
vacuum gauge.
13. Connect the hand vacuum pump to the venturi sensing line
and apply l"-3" of vacuum.
14. If a vacuum reading is present on the gauge this tells
you that vacuum is available to the CTO switch. With a
warm engine the CTO switch should be open to allow vacuum
to the EGR valve. If vacuum is available to the CTO
switch but is not getting to the EGR valve, replace the
CTO switch.
TESTING THE
VENTURI VACUUM EGR SYSTEM
CTO SWITCH
VACUUM
AMPLIFIER
VENTURI
VACUUM
LINE
INTAKE MANIFOLD
VACUUM LINE
EGR VALVE
FIGURE 5-34
If no vacuum is available to the CTO switch replace the
vacuum amplifier.
-------
EGR
5-53
TESTING THE BACK PRESSURE SENSOR EGR SYSTEM
The following procedure can be used to test the back pressure sensor EGR
system.
1. Start with a cold engine.
2. Disconnect the vacuum line at the EGR valve and install
a tee and vacuum gauge. Reconnect the vacuum line to
EGR valve.
EGR VALVE
BACK PRESSURE
SENSOR
(TRANSDUCER)
FIGURE 5-35
3. Start the engine and check the vacuum gauge. It should
read 0".
4. Accelerate the engine to 2000 RPM. The vacuum gauge should
read 0" of vacuum. With the engine coolant temperature low
the CTO switch should be blocking vacuum to the back pressure
sensor and EGR valve.
5. Allow the engine to warm up to normal operating temperature.
6. Accelerate the engine to 2000 RPM. If the CTO switch is
open and the back pressure sensor is operating the vacuum
gauge should read between l"-4" of vacuum. If the gauge
reads 0" of vacuum, follow the following procedure.
-------
5-54
7. Follow the vacuum line that comes from the top connection
of the CTO switch and goes to the exhaust back pressure
sensor.
8. Disconnect the vacuum line at the back pressure sensor
and install a vacuum gauge.
EGR VALVE
BACK PRESSURE
SENSOR
(TRANSDUCER)
FIGURE 5-36
9. Accelerate the engine to 2000 RPM and watch the vacuum
gauge. If there is no reading on the vacuum gauge, the
CTO switch is not operating properly. Replace the CTO
switch. If a vacuum reading appears on the gauge, the
exhaust back pressure sensor is not operating properly.
10. Remove the back pressure sensor and check the exhaust
pressure signal tube for restrictions. If the signal
tube has carbon and/or lead deposits, a spiral wire
brush can be used to clean this area.
11. Re-install the exhaust back pressure sensor.
12. Re-connect the vacuum lines making sure they are installed
correctly.
13. Re-install the vacuum gauge with a tee at the EGR valve.
-------
EGR
5-55
IF NO VACUUM
• CHECK
CONNECTIONS
• INSPECT SPACER
• CLEAN
SENSOR
FIGURE 5-37
14. Start the engine and allow it to come to normal operating
temperature.
15. Accelerate the engine to 2000 RPM and watch the vacuum gauge.
If there is no vacuum reading on the gauge the back pressure
sensor is not operating properly. Replace the exhaust back
pressure sensor, as it connot be serviced.
NOTE: Cars with single exhaust systems use a different
back pressure sensor than cars with a dual exhaust
system. Be sure the one you are going to install
is the proper sensor. If a dual exhaust sensor is
used on a car with a single exhaust system this
will cause a driveability problem.
A dual exhaust sensor operates at a lower back pressure.
If this sensor is used on a vehicle with a single exhaust
system it will result in too much exhaust gas recirculation.
This will cause a large drop in engine power and fuel
economy.
-------
5-56
52. EGR systems should be inspected and tested anytime the
vehicle is being , or when the EGR system is
suspected of not operating properly.
53. If leaded gasoline is used most manufacturers recommend
removing and inspecting the EGR valve every
miles.
54. If unleaded gasoline is used most manufacturers recommend
removing and inspecting the EGR valve every
miles.
55. The CTO switch is not operating properly and should be
replaced if the EGR valve begins to open while the engine
is
56. The CTO switch should be open to allow vacuum to the EGR
valve with a engine.
57. With the engine coolant temperature low the CTO switch
should be blocking to the back pressure
sensor and EGR valve.
60. A dual exhaust sensor operates at a back
pressure than a single exhaust sensor.
-------
EGR
5-57
SYSTEM SUMMARY
PURPOSE
The purpose of the exhaust gas recirculation system is to supply, in the
proper proportion, inert exhaust gas to the air/fuel mixture in the intake
manifold. This dilution of the air/fuel mixture reduces peak flame
temperatures during combustion and reduces the amount of oxides of nitro-
gen (NO ) in the exhaust.
A
MAIN COMPONENTS
EGR Valve - Meters or shuts off exhaust gas flow to the air/fuel side of
the intake manifold.
Intake Manifold - Contains specially cast exhaust passages that connect
to the intake side of the manifold through the EGR valve.
Carburetor Signal Port (on ported vacuum controlled EGR) - Located in the
carburetor throttle body to sense manifold vacuum and control the EGR valve.
Venturi Vacuum Signal Tap (on Venturi Vacuum controlled EGR) - Located on
carburetor throat to sense venturi vacuum signal. This signal is trans-
mitted through a vacuum amplifier to control manifold vacuum to regulate
the EGR valve.
Temperature Controlled Vacuum Valve - Prevents vacuum from reaching and
operating the EGR valve until radiator top tank temperature reaches approx-
imately 16°C (60°F).
SYSTEM FUNCTION
In order for the EGR system to operate, a manifold vacuum signal must reach
the EGR valve. Vacuum can be sensed and directed to the EGR valve between
idle and full throttle engine operation. The EGR system will not operate
at idle or full throttle - only between these two conditions. However, a
vacuum signal cannot reach the EGR valve under any conditions until the
radiator top tank temperature or engine coolant temperature has reached
-------
5-58
approximately 60°F. This assures good cold engine driveabiltiy. When
in operation, the EGR system will divert a regulated amount of exhausted
gases from the exhaust manifold back into the intake manifold to be
mixed with the fresh air/fuel charge. This process reduces combustion
temperatures and helps eliminate oxides of nitrogen (NO ) from auto
emissions.
-------
ANSWERS
EGR
5-59
1. exhaust 30.
2. exhaust 31.
3. nitrogen 32.
4. 2500°F 33.
5. inert 34.
6. lower 35.
7. NO 36.
H
8. Exhaust Gas Recirculation 37.
9. intake manifold 38.
10. valve 39.
11. vacuum 40.
12. no 41.
13. port 42.
14. venturi 43.
15. zero 44.
16. increases 45.
17. coolant temperature override 46.
18. coolant temperature 47.
19. vacuum 48.
20. ambient 49.
21. EGR 50.
22. venturi 51.
23. intake manifold 52.
24. pressure 53.
25. vacuum 54.
26. exhaust 55.
27. surge 56.
28. high 57.
29. prevent 58.
35 seconds
vacuum solenoid
timer control or delay timer
closed
spring
valve
air/fuel
sealed
two
carburetor
intake manifold
ported
acceleration
N0x
ball
open
intake manifold
high
ported vacuum
testing
service manual
vacuum
tuned up
12,000
25,000
cold
warm
vacuum
lower
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
EPA-450/3-77-040
TITLE A \DSU3TITLE
Motor Vehicle Emissions Control - Book Five
Exhaust Gas Recirculation Systems
3. RECIPIENT'S ACCESSIOWNO.
S. REPORT DATE
November 1977
6. PERFORMING ORGANIZATION CODE
7. AUTHOR'S)
H.D. Hayes
M.T. Maness
8. PERFORMING ORGANIZATION REPORT NO.
R.A.
R.A.
Ragazzi
Barrett
P£F!F:OPMiNG ORGANIZATION NAME ANDADDRESS
Department of Industrial Sciences
Colorado State University
Fort Collins, Colorado 80523
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
T008135-01-0
T900621-01-0
'. SPONSORING AGENCY NAME AND ADDRESS
Control Programs Development Division
Office of Air Quality Planning and Standards
Office of Air and Waste Management
U.S. Environmental Protection Agency
13. TYPE OF REPORT AND PERIOD COVERED
Final Report
14. SPONSORING AGENCY CODE
EPA 200/04
15. SUPPLEMENTARY NOTES Research Triangle Park, North Carolina 27711
16. ABSTRACT
This book is one of a series designed specifically to teach the concepts of auto-
mobile emissions control systems. It is intended to assist the practicing mechanic
or the home mechanic to better understand the Exhaust Gas Recirculation Systems
which are an integral part of automobiles today. The mechanic's increased know-
ledge should help him keep "emissions controlled" vehicles operating as designed.
Respectable fuel economy, performance and driveability, as well as cleaner air, can
be obtained from the automobile engine that has all of its emissions systems
functioning properly.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lOENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air Pollution
Exhaust Gas Recirculation
Photochemical
Intake Manifold
System Inspection
Hydrocarbons
Carbon Monoxide
Oxides of
Nitrogen
Carburetor
Vacuum Sole-
noid
Acceleration
13. DISTRIBUTION STATEMENT
Release Unlimited
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
65
20. SECURITY CLASS (Thispagt)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
*U.S. GOVERNMENT PWhTTING OFFICE: 1978 -7«t 5 - 22
------- |