EPA-450/3-77-041'
'November 1977
MOTOR VEHICLE
EMISSIONS CONTROL
BOOK SIX
SPARK CONTROL SYSTEMS
•V,'..'.
•
• V. »• .•:
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
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EPA-450/3-77-041
M MOTOR VEHICLE EMISSIONS CONTROL
BOOK SIX
SPARK CONTROL 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
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Copies of this publication are available free of charge to Federal employees,
current contractors and grantees, and nonprofit organizations - as supplies
permit - from the Library Services Office (MD-35), Environmental Protection
Agency, Research Triangle Park, North Carolina 27711; or, for a fee, from
the National Technical Information Service, 5285 Port Royal Road, Springfield
Virginia 22161.
This report was furnished to the Environmental Protection Agency by the
Department of Industrial Sciences, Colorado State University, Fort Collins,
Colorado, 80523, through Grant No. 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-450/3-77-041
11
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MOTOR VEHICLE EMISSIONS CONTROL
-- SERIES OF SEVEN BOOKS --
MOTOR VEHICLE EMISSIONS STAFF, COLORADO STATE UNIVERSITY
BOOK ONE - POSITIVE CRANKCASE VENTILATION SYSTEMS
BOOK TWO - THERMOSTATIC 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
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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, 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
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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.
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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.
vt
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CONTENTS
Introduction to Emissions Control 6-1
Hydrocarbons 6-1
Carbon Monoxide 6-1
Oxides of Nitrogen 6-2
Formation of Hydrocarbons 6-2
Formation of Carbon Monoxide 6-3
Formation of Oxides of Nitrogen 6-3
Ignition Timing 6-3
Carburetion 6-5
System Introduction 6-7
System/Component Purpose 6-13
Vacuum Solenoid Valve 6-13
Transmission Switch 6-14
Cold CTO Switch 6-17
Hot CTO Switch 6-18
ESC Solenoid Vacuum Control Valve 6-19
Speed Sensor 6-20
Electronic Amplifier 6-21
Ambient Temperature Switch 6-21
TRS Transmission Switch 6-22
Spark Delay Valve 6-23
OSAC Valve 6-24
System/Component Function 6-27
Vacuum Solenoid Valve 6-27
Transmission Switch 6-30
Spark Control System 6-33
Cold CTO Switch 6-35
Hot CTO Switch 6-38
Thermal Vacuum Switch 6-42
Electronic Spark Control System 6-43
Transmission Regulated Spark System 6-44
Spark Delay System 6-45
Orifice Spark Advance Control System 6-47
vti
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viii
CONTENTS (cont.)
System Inspection 6-49
System Testing 6-51
Testing the TCS System 6-51
Testing the ESC System 6-54
Spark Delay Valve Test 6-55
OSAC Valve Test 6-56
Summary 6-59
Answers 6-61
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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.
6-1
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6-2
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
rt
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.
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6-3
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
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6-4
exerted on the piston. As a result the best performance and fuel econ-
omy could be obtained. Unfortunately, this also produced 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.
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6-5
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
amoung 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.
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sc
6-7
SYSTEM INTRODUCTION
In the introduction of this book you learned that photochemical smog was
formed when oxides of nitrogen and hydrocarbons combine in the presence
of sunlight. You have also learned about the emissions control systems
which reduce the hydrocarbon emissions, as well as the EGR system used
to reduce the oxides of nitrogen (NO ) emissions. It is now time for you
J\
to learn about the spark control system. This system, like the EGR
system, is designed to help reduce oxides of nitrogen or NOX emissions.
It also helps to reduce hydrocarbon emissions.
Spark control systems as we know them today first began to appear on
automobile engines in the very late 1960's and early 1970's. As with
many of the other systems we have discussed, the spark control system is
not installed on all automobile engines. The spark control system was
installed on those vehicles needing it to meet federal regulations. A
large number of American and foreign automobiles are equipped with a
spark control system.
The spark control system helps to reduce the amount of oxides of nitrogen
emitted from the automobile's tailpipe. As you recall from the introduc-
tion, oxides of nitrogen are formed in the combustion chamber. The
spark control system is designed to lower the amount of NO which is
/\
formed during the combustion process. Since less amounts of NO are
* /\
formed in the combustion chamber, there is less NOX which will be
emitted from the tailpipe. This in turn will help to reduce the forma-
tion of photochemical smog.
In addition, the spark control system helps reduce hydrocarbon emissions.
Unlike the reduction of NO emissions, the HC emissions are controlled
A
or reduced after they leave the combustion chamber. These hydrocarbons
are burned in the exhaust manifold after they leave the combustion
chamber. By reducing the HC emissions the spark control system helps
to control the other important component of photochemical smog. This
system reduces both HC and NO .
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6-8
FIGURE 6-1
The period when the most oxides of nitrogen and hydrocarbons are emitted
from the tailpipe is when the engine is under a heavy load. When a
vehicle is accelerating, climbing hills or towing a trailer the engine
will be in a loaded condition. When the engine is loaded in this manner,
the air/fuel ratio entering the combustion chamber will be relatively
rich. This rich condition will raise the HC emissions. The throttle
plates will also be opened fairly wide when the engine is under load.
With these conditions the combustion chamber pressures and temperatures
will be high. As you recall from the introduction, oxides of nitrogen
are formed when high temperatures in the combustion chamber occur. Now
that you have a basic understanding of when the larger amounts of HC and
NO are formed, we will take a look at how they are controlled.
/\
The spark control system actually controls the ignition timing of the
engine. This system will prevent the vacuum advance from operating under
certain engine conditions. By preventing vacuum advance the spark plug
will fire later in the compression stroke. When this occurs, not as much
heat energy will be exerted on the piston. The extra heat energy will be
released in the exhaust manifold during the exhaust stroke.
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sc
6-9
Since preventing vacuum advance causes less heat energy to be exerted on the
piston the combustion chamber temperatures will be lower. You know that the
formation of oxides of nitrogen depends on high temperatures. Since the
combustion temperatures are reduced with the use of a spark control system,
the formation of NO will be reduced. This is how the spark control system
y\
reduces oxides of nitrogen.
Preventing vacuum advance also causes the exhaust gas temperature to increase
Since there is a higher exhaust gas temperature, the hydrocarbons will con-
tinue to burn or oxidize in the exhuast manifold. Preventing vacuum advance
will also cause the idle RPM to drop. By opening the throttle plates wider
the idle speed can be brought back to an acceptable level. This will allow
additional air into the combustion chamber and aid in further oxidizing the
hydrocarbons. So you can now see that the additional air and the hotter
exhaust temperatures will lower the HC emissions.
LARGER
THROTTLE
OPENING
HOTTER EXHAUST
TEMPERATURE
FIGURE 6-2
1. The spark control system aids in reducing the amount of
emitted from the auto-
mobile 's tailpipe.
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6-10
2. The spark control system is designed to lower the amount
of NO which is formed during the
3. are also reduced
by the spark control systems.
4. The hydrocarbons are controlled by burning in the
after they leave the
combustion chamber.
5. The condition when the most oxides of nitrogen and hydro-
carbons are emitted from the tailpipe is when the engine
is under
6. of the engine is controlled
by the spark control system.
7. The combustion chamber temperature will be lower when
vacuum advance is denied. This causes less heat energy
to be exerted on the
g. temperatures increase when vacuum
advance is denied.
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sc
6-11
You should now have a basic understanding of how the spark control system
controls hydrocarbons and oxides of nitrogen. It is now time to study
the purpose of the components in the spark control system and how they
work.
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6-13
SYSTEM/COMPONENT PURPOSE
The purpose of any spark control system is to prevent or delay distribu-
tor vacuum advance during certain periods of engine operation. By
preventing advanced spark timing, oxides of nitrogen and hydrocarbon
emissions will be reduced. The greatest amount of oxides of nitrogen and
hydrocarbons are produced when the engine is under a heavy load. There-
fore, the purpose of the spark control system is to prevent advanced
ignition spark during periods of heavy engine load. An automobile engine
can achieve better fuel economy if it has an advanced ignition spark.
For this reason, the spark control system must provide an advanced spark
when the automobile is cruising and the engine is not heavily loaded.
In our discussion of the spark control system, we will first look at some
individual components used in this system. Once you know the purpose of
these components, we will look at how they work together as a system.
VACUUM SOLENOID VALVE
The first component we will discuss is the vacuum solenoid valve. Figure
6-3 shows a typical vacuum solenoid valve found in many spark control
systems.
VACUUM ADVANCE
SHUT OFF IN
LOWER GEARS
FIGURE 6-3
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6-14
The purpose of the vacuum solenoid valve is to block or prevent vacuum
from reaching the vacuum advance unit on the distributor. This in done
only when the engine is accelerating from low speeds. When the auto-
mobile is at cruising speed the vacuum solenoid valve will allow vacuum
to reach the advance unit on the distributor. The vacuum solenoid
valve has one other job to do. This is to vent air into the vacuum
advance unit whenever the solenoid denies vacuum.
The vacuum solenoid valve is triggered to allow or deny vacuum advance
by an electrical circuit. This electrical circuit is controlled by a
switch on the transmission.
9. An spark will allow an
automobile engine to achieve better fuel economy.
TRANSMISSION SWITCH
The next component in the spark control system we will look at is the
transmission switch. You know that the spark control system prevents
vacuum advance when the engine is accelerating from low speeds. The
automobile manufacturers found that nearly all heavy load operation of
the automobile occured when the transmission is in the lower gears. For
this reason if vacuum advance was denied in all the lower gears, the NO
A
and HC could be reduced. Nearly all of the cruising engine operation
occurs when the transmission is in high gear. So if vacuum advance was
allowed in high gear the desired fuel economy could be obtained at
cruising speeds. This is how many spark control systems work. On a
car with a three speed automatic or manual transmission, vacuum advance
will be blocked in first and second gears. The engine would be allowed
vacuum advance in third gear. A car with a four speed manual transmission
will have vacuum advance denied in first, second and third gears and it
would be allowed vacuum advance in fourth gear. The transmission switch
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sc
6-15
and the vacuum solenoid valve are the components of the spark control
systems which make this happen.
Figure 6-4 shows two transmission switches. These are electrical
switches which are connected to the transmission. The electrical circuit
through the switch can either be open or closed.
MANUAL AUTOMATIC
TRANSMISSION SWITCH TRANSMISSION SWITCH
(OPENS IN HIGH GEAR) (OPENS AT 35 MPH)
FIGURE 6-4
When the switch is open, no current will flow through the circuit.
When the switch is closed, current will pass through the switch and
the rest of the circuit. The purpose of the transmission switch is to
control the operation of the vacuum solenoid valve. It is connected to
the transmission so it will switch positions and trigger the vacuum
solenoid valve when the transmission shifts into high gear. In this
manner, the transmission switch and the vacuum solenoid valve will
allow vacuum advance only in high gear. Figure 6-5 shows how these
components are connected together in the system.
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6-16
CARBURETOR
TRANSMISSION
SWITCH
SOLENOID VACUUM
SWITCH
DISTRIBUTOR
IGNITION
FIGURE 6-5
10. The valve's purpose is to
block or prevent vacuum from reaching the vacuum advance
diaphragm on the distributor.
11. An
triggers the
vacuum solenoid valve to allow or deny vacuum advance.
12. A switch on the
controls the
electrical circuit.
13. On a car with a three speed automatic transmission,
vacuum advance will be blocked in both _
gears.
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sc
6-17
14. The purpose of the transmission switch is to control the
operation of the valve.
COLD CTO SWITCH
Automobile manufacturers found that this spark control system worked well
most of the time. However, when the engine was cold, the automobile
suffered from driveability problems if vacuum advance was denied by the
system. For this reason a cold temperature override or CTO switch was
added to the system. This switch improved cold engine driveability. A
CTO switch is shown in figure 6-6. .
CTO
SWITCH
COOLANT
TEMPERATURE
OVERRIDE
SWITCH
FIGURE 6-6
The purpose of the cold temperature override or CTO switch, is to allow
full manifold vacuum to the vacuum advance unit when the engine is cold.
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6-18
HOT CTO SWITCH
There is also a hot coolant temperature override switch built into the
spark control system on some automobiles. This switch is called a hot
override. Figure 6-7 shows a hot override switch.
HOT-COOLANT OVERRIDE SWITCH
l.CARBURETOR
VACUUM
DISTRIBUTOR
ADVANCE
PORT
~ MANIFOLD
1 VACUUM
COOLANT
TEMPERATURE
SENSOR
FIGURE 6-7
This switch looks just like a CTO swtich. The purpose of the hot over-
ride switch is to allow full manifold vacuum to reach the advance unit
on the distributor when the engine becomes too hot.
As you probably know, the vacuum used to advance the spark on most newer
cars is ported vacuum. This means that the vacuum signal is picked up
from a small port just above the throttle plate. For this reason, there
is no ported vacuum at idle and no vacuum advance at idle. However, the
CTO and hot override switches direct full manifold vacuum to the advance
unit when the engine is either too cold to too hot. This manifold
vacuum will immediately advance the spark. This will cause the idle RPM
to increase which will result in more efficient cooling for the hot
engine and will allow a faster warm-up for the cold engine. When the
engine reaches a normal operating temperature after being either too
cold or too hot the override switch will again direct ported vacuum to
the advance unit.
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sc
6-19
15. To improve cold engine driveability/ a
switch has been
installed in the transmission control spark system.
16. The purpose of the CTO switch is to allow
to the vacuum advance unit on the
distributor when the engine is cold.
17. The purpose of the
switch is to
allow full manifold vacuum to reach the advance unit on
the distributor when the engine becomes too hot.
ESC SOLENOID VACUUM CONTROL VALVE
Another spark control system called the ESC or Electronic Spark Control
system has components which do the same job as those we have just discussed.
The first component of this system we shall discuss is the solenoid vacuum
control valve. This valve may be seen in figure 6-8. The purpose of the
SOLENOID VACUUM CONTROL VALVE
ENERGIZED DE-ENERGIZED
ELECTRIC
T0 t J CURRENT
CARB.
ELECTRIC
CURRENT
APPLIED
VACUUM BLOCKED
VACUUM ALLOWED
FIGURE 6-8
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6-20
solenoid vacuum control valve is exactly the same as the vacuum solenoid
valve which we discussed. The purpose of both solenoid valves is to deny
or prevent vacuum from reaching the advance unit on the distributor.
When either of these valves are denying vacuum advance they will also
vent the line which connects to the advance unit on the distributor.
This will assure the removal of the extra advance provided by the
distributor vacuum advance unit. Remember that the solenoid valves
deny vacuum advance only when the engine is accelerating from low speeds.
18
Another spark control system called the
Control system has components which do the same
job as the other spark control systems.
19. When the engine is
from low
speeds the solenoid valve denies vacuum advance.
SPEED SENSOR
Figure 6-9 shows the next component of this spark control system we will
SPEED SENSOR
FIGURE 6-9
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sc
6-21
discuss. This component is the speed sensor. The speed sensor's purpose
is to generate a small voltage signal. The speed sensor is connected to
the speedometer cable and senses how fast the automobile is moving. The
voltage signal produced by the speed sensor increases as the vehicle
speed increases.
ELECTRONIC AMPLIFIER
The speed sensor signal is sent to an electronic amplifier. Two electronic
amplifiers are shown in figure 6-10.
DIFFERENT COLORS DESIGNATE
DIFFERENT CUT-IN SPEEDS
23MPH
33 MPH
FIGURE 6-10
The purpose of the electronic amplifier is to control the solenoid vacuum
valve's operation. The electronic amplifier will trigger the solenoid
vacuum valve to either allow or deny vacuum to the vacuum advance unit on
the distributor. The electronic amplifier determines when to do this by
the signal received from the speed sensor.
AMBIENT TEMPERATURE SWITCH
This ESC system also has an ambient temperature switch to help cold
engine driveability. This temperature switch is shown in figure 6-11.
The purpose of the ambient temperature switch is to override the ESC
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6-22
TO IGNITION SWITCH
TO VACUUM
SOLENOID
VALVE
FIGURE 6-11
system and allow full vacuum advance to reach the distributor. This
switch will override the system when the outside air temperature 1s below
50°F.
20. The purpose of the speed sensor is to generate a small
21. The
purpose
is to control the solenoid vacuum valve operation.
TRS TRANSMISSION SWITCH
Another system called the TRS or Transmission Regulated Spark system is
very similar to the ESC system. This system, however, uses a transmission
switch instead of the speed sensor and the electronic amplifier. The
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sc
6-23
purpose of the transmission switch, as you should recall, is to trigger
the solenoid vacuum valve to either allow or deny vacuum to pass on to
the distributor vacuum advance unit.
SPARK DELAY VALVE
Another very simple spark control system is the spark delay system.
There is only one component in this system. This component is the spark
delay valve. This valve is shown in figure 6-12. The purpose of the
SPARK DELAY VALVE
5 SEC.
8 SEC.
16 SEC.
FIGURE 6-12
spark delay valve is to simply delay the vacuum from reaching the vacuum
advance unit on the distributor. Whenever the vacuum advance signal drops
to approximately 0" Hg, the valve will vent the vacuum line and the
vacuum advance will be denied. This will occur whenever the throttle
plates are closed or fully open. When the vacuum advance signal again
increases, the spark delay valve will delay this vacuum signal from
reaching the advance unit for a few seconds. After a few seconds vacuum
advance will be allowed.
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6-24
22,
TRS stands for
system.
23. Instead of using the speed sensor and electronic
amplifier the TRS system uses a
switch.
OSAC VALVE
The last spark control system is very similar to the spark delay system
we just discussed. The system uses an Orifice Spark Advance Control
Valve or (OSAC) valve. This valve is shown in figure 6-13.
TO
DISTRIBUTOR
PORTED
VACUUM
OSAC
VALVE
FIGURE 6-13
The OSAC valve is very similar to the spark delay valve. The purpose of
the OSAC valve is to delay the vacuum signal from reaching the distributor
vacuum advance unit for a few seconds. This valve works in the same
-------
sc
6-25
manner as the spark delay valve. The OSAC valve may however, have a
temperature control unit built into its housing. The temperature control
unit simply by-passes the delay portion of the valve when the air
temperature is below 60°F. When the air is below 60°F the vacuum signal
is not delayed but is allowed to the advance diaphragm immediately.
24. The system is another very simple
spark control system.
25. The purpose of the spark is to
delay the vacuum from reaching the vacuum advance unit
on the distributor.
26. OSAC stands for
27. The purpose of the OSAC valve is to delay the vacuum
signal from reaching the
diaphragm for a few seconds.
Now you should be aware of the purpose of the various spark control system
components. We will now move on to the function of these components and
the systems themselves.
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sc
6-27
SYSTEM/COMPONENT FUNCTION
In the purpose section of this book you learned about the components of
the spark control system. You should be familiar with the job each of
the components must do. In this section we will take a look at how these
components do their jobs. Once you know how each component does its job,
you will learn how these components work together in the spark control
system.
VACUUM SOLENOID VALVE
The vacuum solenoid valve is the first component we will discuss. As
you recall the purpose of the vacuum solenoid valve is to allow or prevent
vacuum from reaching the advance unit on the distributor. It must also
vent the line to the advance unit when the vacuum is being denied.
Figure 6-14 shows the inside of a typical vacuum solenoid valve. As you
can see in figure 6-14, inside the main body of the vacuum solenoid valve
1s a wire coil and a small rod. On the outside of the vacuum solenoid
COIL
ROD
VACUUM ADVANCE
SHUT OFF IN
LOWER GEARS
FILTER
FIGURE 6-14
valve are two electrical terminals. There terminals are connected to both
ends of the wire coil. When current flows through the wire coil, a
-------
6-28
magnetic field will be produced. This magnetic field will collapse or
disappear when the current is removed from the wire coil.
The small metal rod inside the vacuum solenoid valve moves in the magnetic
field created bythewire coil. When no current is flowing through the
wire coil, the metal rod will be in the position shown in figure 6-15.
VACUUM SOLENOID
VALVE (DE-ENERGIZED)
CARBURETOR
VENT
DISTRIBUTOR
FIGURE 6-15
When the rod is in this position it will block off the filtered vent
passageway. This is the position the valve will be in when it is allow-
ing vacuum advance. When the valve is in this position the air in the
advance unit will be drawn through the hose connection which connects the
valve to the advance unit. This air will then be drawn past the metal
rod and out of the valve to the vacuum source. Once this air has been
removed the vacuum advance unit will be in the advanced position. This
is shown in figure 6-15.
When current flows through the wire coil the metal rod is pulled to the
carburetor end of the valve. In this position, the filtered vent will
allow air to pass through the valve and into the advance unit. This
will eliminate all spark advance caused by the vacuum advance unit. The
end of the metal rod will also block the vacuum source hose connection
and prevent any vacuum from moving beyond the valve.
-------
sc
6-29
The flow of current through the vacuum solenoid wire coil is controlled
by the automobile's ignition switch and the transmission switch. These
switches are connected in a series circuit. For this reason both
switches must be closed to complete the circuit and energize the vacuum
solenoid valve. Whenever the ignition switch is in the engine run
position it is closed. For this reason the transmission switch is what
controls the vacuum solenoid valve.
28. Located inside the main body of the vacuum solenoid valve
is a small rod and a
29. Two are located on
the outside of the vacuum solenoid valve.
30. The small metal rod inside the vacuum valve moves in the
created by current flow in
the wire coil.
31. When flows through the wire coil the metal
rod is pulled to one end of the valve.
32. The automobile's' and the
transmission switch control the flow of current through
the vacuum solenoid wire coil.
-------
6-30
33. The ignition and transmission switches are connected in
a circuit.
TRANSMISSION SWITCH
The transmission switch, vacuum solenoid valve, and the ignition switch
are connected together as shown in figure 6-16. The transmission switch
is an on-off switch. This means that it can only be open or closed or
that it can only block or pass current.
VACUUM
SOLENOID
VALVE
TRANSMISSION
SWITCH
FIGURE 6-16
The transmission switch used for automobiles equipped with automatic
transmissions is connected into the hydraulic circuit of the transmission.
This switch senses hydraulic pressure in the transmission. Figure 6-17
shows when the switch is open or closed. As you can see in figure 6-17,
the switch will open and block current flow when the automobile speed
reaches 35 MPH or higher. The switch will be closed and pass current
whenever the automobile is moving slower than 35 MPH. The transmission
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sc
6-31
AUTOMATIC TRANSMISSIONS
CLOSED OPEN
BELOW 35 MPH
OR LOWER GEARS
ABOVE 35 MPH
OR HIGH GEAR
FIGURE 6-17
switch knows how fast the automobile is moving because it senses hydrau-
lic pressure in the transmission. The end of the transmission switch
which connects to the transmission has a small pressure sensor built into
it. As the speed of the automobile changes, the hydraulic pressure
changes. When the automobile reaches a speed of approximately 35 MPH,
the hydraulic pressure will change to the point where it will trigger
the sensor, which in turn will open the electrical part of the switch.
When this happens, current; can no longer flow through the transmission
switch and the vacuum solenoid valve will de-energize. As you already
know, when this happens vacuum will be allowed to the vacuum advance unit
on the distributor.
The transmission switch used on automobiles equipped with manual trans-
missions are very similar to the automatic transmission switch. The
manual transmission switch however, is not triggered by a pressure sensor.
The manual transmission switch is mounted on the transmission so when the
automobile is shifted into high gear the shift linkage comes in contact
with the switch. Figure 6-18 shows the electrical condition of the switch
when the transmission is in the lower gears and when it is in high gear.
As you can see when the transmission is in the lower gears, the linkage is
-------
6-32
MANUAL TRANSMISSIONS
CLOSED OPEN
LOW GEARS
HIGH GEAR
FIGURE 6-18
not in contact with the switch. In this position the switch will remain
closed and current will pass through the switch. This will energize the
vacuum solenoid valve and block the vacuum signal from reaching the advance
unit. However, when the transmission is shifted to high gear, the shift
linkage will contact the transmission switch. This will open the switch
and stop the current flow through the circuit. As you know, when this
current flow stops, the vacuum solenoid valve de-energizes and the engine
is allowed vacuum advance.
34. The
switch is an on-off switch.
35. The transmission switch used with automatic transmissions
knows how fast the automobile is moving because it senses
in the transmission.
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sc
6-33
36. The manual transmission switch is triggered by physical
contact with the shift
37. The vacuum solenoid valve will be
when the transmission switch is open.
SPARK CONTROL SYSTEM
Now you should understand the function of the vacuum solenoid valve and
the transmission switch circuit. You probably understand how they work
together to prevent or allow vacuum advance. However, we will now look
at these components in the system and see how they work together.
Figure 6-19 shows this spark control system with the automobile in high
gear or above 35 MPH. As you know, when the automobile is traveling at
this speed, the transmission switch is open. This is shown in figure 6-19.
When the switch-is open the vacuum solenoid valve will be de-energized.
SOLENOID VACUUM
SWITCH
DISTRIBUTOR
TRANSMISSION
SWITCH
IGNITION
FIGURE 6-19
-------
6-34
As you can see in figure 6-19, when the valve is de-energized, the valve
rod moves down and seals the filtered vent on the end of the vacuum
solenoid valve. In this position, the vacuum will pass through the
valve by going around the metal rod. It will then move on to the
distributor vacuum advance unit. The system, when it is in this position,
will allow vacuum advance.
Figure 6-20 shows the spark control system when the vehicle is in a lower
gear or below 35 MPH. When the vehicle is traveling at this lower speed,
the transmission switch will be closed and current will flow through the
circuit. As you can see in figure 6-20, when current flows through the
SOLENOID VACUUM
SWITCH
DISTRIBUTOR
TRANSMISSION
SWITCH
CARBURETOR
IGNITION
FIGURE 6-20
circuit the metal rod will be pulled to the opposite end of the vacuum
solenoid valve. This rod will seat against the upper connection of the
valve and block the vacuum at that point. In this position, the engine
will be denied vacuum advance. When the rod moves to the opposite end
of the valve the filtered vent will be exposed. When this happens,
outside air will move into the valve, connecting line, and vacuum advance
unit. This can be seen in figure 6-21. For this reason the engine will
be permitted no vacuum spark advance
-------
sc
6-35
NO SPARK ADVANCE
FIGURE 6-21
COLD CTO SWITCH
The next component of this spark control system we will look at is the
CTO or coolant temperature override switch. Figure 6-22 shows a cut-away
view of a CTO switch. The CTO switch is mounted in such a way that the
lower portion of the switch is in contact with the engine coolant. This
is how a CTO switch senses coolant temperature. As you can see in figure
6-22, the CTO switch has three hose connections on the switch body.
CTO
SWITCH
COOLANT
TEMPERATURE
OVERRIDE
SWITCH
FIGURE 6-22
-------
6-36
Inside the switch body is a small ball and a spring. One other important
substance is in the CTO switch which you can't readily see. This sub-
stance is a heat-sensitive paste which controls the operation of the CTO
switch. This heat-sensitive paste will expand as it takes on heat from
the engine coolant. As this paste expands it will push the ball up
against spring pressure. In this way, when the paste is cold and con-
tracted, the ball will be in the lower portion of the switch body.
When the paste is hot and has expanded, the ball will be in the upper
part of the valve body. Now we will look at how the CTO switch is used
to further control the operation of the spark control system.
Figure 6-23 shows how the CTO switch is connected into the spark control
system we have been discussing. As you can see in figure 6-23, the
upper hose connection of the CTO switch is connected to a manifold vacuum
TO IGNITION
SWITCH
OPEN OVER
35MPH
OR HIGH GEARS
FIGURE 6-23
source. The middle connection goes to the vacuum advance unit on the
distributor. The lower connection is connected to the solenoid vacuum
switch. You will recall that this hose went to the vacuum advance unit
on the distributor on the system we just discussed. Figure 6-23 shows
this spark control system with a cold engine. The paste in the CTO
switch is cold and contracted. For this reason the ball is in the lower
portion of the switch body.
-------
sc
6-37
When the CTO switch is in this position, the manifold vacuum signal is
allowed to pass to the spark advance unit on the distributor. This may
be seen in figure 6-23. Since the engine is cold this will aid drive-
ability and help warm the engine more quickly.
As the engine coolant approaches approximately 160°F, the paste in the
CTO switch will be fully expanded and the ball will be in the upper
portion of the switch body. This condition is shown in figure 6-24.
ABOVE I6O-F
TO IGNITION
SWITCH
OPEN OVER
35MPH
OR HIGH GEARS
FIGURE 6-24
When the CTO switch is in this position, the spark control system will
operate exactly as the first spark control system we discussed. Figure
6-24 shows the system when the automobile is in high gear. With this
condition, the vacuum signal will pass through the solenoid vacuum switch
then through the CTO switch and on to the vacuum advance unit. If the
transmission shifts to any of the lower gears, the solenoid vacuum switch
will block vacuum from reaching the advance unit on the distributor.
38. The lower portion of the CTO switch is in contact with
the
-------
6-38
39. An important substance in the CTO switch is a
paste which controls the operation of
the switch.
40. The paste in the CTO switch will be fully expanded as the
engine coolant approaches approximately 160°F. The ball
in the CTO switch will be in the
of the switch body.
HOT CTO SWITCH
You will remember from the purpose section of this book that a hot coolant
temperature override switch was built into some spark control systems to
help cool the engine if it began to overheat. We will now see how this
device functions and how it is connected into the spark control system.
Figure 6-25 shows a cut-away view of a hot coolant temperature override
switch. As you can see, the hot coolant temperature override switch looks
HOT-COOLANT OVERRIDE SWITCH
..CARBURETOR
{ VACUUM
, ^DISTRIBUTOR
/ADVANCE
, MANIFOLD
1 VACUUM
COOLANT
TEMPERATURE
SENSOR
FIGURE 6-25
-------
sc
6-39
very similar to a cold coolant temperature override switch. It also
functions the same way as a cold CTO switch.
The hot override CTO switch is built exactly like the CTO switch we just
discussed. As with the cold override, the paste in the switch expands
when it gets hot. The temperature at which the ball starts to move up-
ward in the switch body, however, is much higher in a hot override
switch. When the coolant temperature is below approximately 225°F, the
ball valve will be in the lower portion of the switch body. When the
ball valve is in this position, the upper two hose connections will be
linked together. The switch in figure 6-25 is in this position.
As the coolant temperature approaches about 225°F, the ball will start
to move upwards. When the coolant temperature is above 225°F the ball
will be positioned in the upper portion of the valve body. When the ball
is in this position the lower two hose connections will be linked to-
gether. The hot coolant temperature override switch will move to this
position when the engine is overheating.
As you can see in figure 6-25, the upper hose connection of the hot CTO
switch connects to the carburetor or ported vacuum source. The lower
hose connection attaches to a manifold vacuum source. The center hose
connection on the CTO switch is the distributor advance port.
With hose connections arranged in this manner, the desired vacuums will
be routed to the distributor during the proper engine conditions. We
will now look at the hot override switch in the spark control system.
Figure 6-26 shows how the hot override switch is connected into the
spark control system. As you can see in figure 6-26, the engine coolant
temperature is between 160°F and 225°F. Since this is the case, neither
override switch will allow manifold vacuum to the advanct unit. As you
can see in figure 6-26, ported vacuum is allowed to pass through both
switches and on to the vacuum advance unit on the distributor. As you
-------
6-40
BELOW 225°F-ABOVE I60°F
PORTED
VACUUM
-CTO
HOT OVERRIDE
PORTED
VACUUM
FIGURE 6-26
recall, when the coolant temperature reaches about 225°F, the ball in the
hot override will move upwards in the switch body. This will direct mani-
fold vacuum to the vacuum advance unit on the distributor. This condition
is shown in figure 6-27. When the coolant temperature drops below 225°F,
the hot CTO switch will again direct ported vacuum to the advance unit.
ABOVE 225°F
HOT OVERRIDE
PORTED
VACUUM
-CTO
MANIFOLD
VACUUM
FIGURE 6-27
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sc
6-41
Now you should understand how the hot coolant temperature override
switch works in this spark control system.
Figure 6-28 shows this spark control system with the vacuum solenoid
valve. Remember that the vacuum solenoid valve will allow or block
ported vacuum to the distributor. It will either allow or block ported
vacuum depending on which gear the transmission has been shifted to.
PORTED
VACUUM
-CTO
HOT OVERRIDE
PORTED
VACUUM
FIGURE 6-28
If the engine coolant is either above 225°F or below 160°F, a CTO switch
will direct manifold vacuum to the advance unit. When the engine reaches
normal operating temperature ported vacuum will again be used to advance
the spark.
41. The upper hose connection of the CTO switch connects to
vacuum.
-------
6-42
42. When the coolant temperature reaches about 225°F, the
ball in the _^ will move upward in
the switch body.
THERMAL VACUUM SWITCH
General Motors has used a slightly different hot override switch for their
spark control system. This switch is called a Thermal Vacuum Switch.
This switch does the same job as the hot CTO switch. The inside of this
switch is slightly different, however. As you can see in figure 6-29,
this switch has a small piston instead of a ball in the switch body. The
G.M. THERMAL VACUUM VALVE
HOT OVERRIDE NORMAL ADVANCE
POSITION POSITION
D-TO DIS-
TRIBUTOR —T]
C-TO PORTEDL
VACUUM
MT-TO INTAKE
MANIFOLD
FIGURE 6-29
vacuum signal passes through the switch in a different fashion. For this
reason, the vacuum line connections are arranged differently. This can
also be seen in figure 6-29. Since these thermal vacuum switches look
much the same as the hot CTO switch, but have different hose connections,
it is very important to check the manufacturer's specifications for
servicing any specific engine.
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sc
6-43
ELECTRONIC SPARK CONTROL SYSTEM
The next spark control system you will study is the ESC or Electronic
Spark Control system. Figure 6-30 shows the components of the ESC system.
The electronic amplifier is the heart of the ESC system. The electronic
amplifier either energizes or de-energizes the vacuum solenoid valve.
The amplifier does this by the messages it receives from the ambient
temperature switch and the speed sensor.
ELECTRONIC SPARK CONTROL
CARBURETOR
DISTRIBUTOR
SOLENOID
VACUUM VALVE
TEMPERATURE.
SWITCH
ELECTRONIC
AMPLIFIER
FIGURE 6-30
If the ambient air temperature is below approximately 65°F, the vacuum
solenoid valve will be de-energized. This will allow the vacuum signal
to reach the advance unit on the distributor. When the ambient air
temperature is above 65°F, the electronic amplifier will energize the
vacuum solenoid valve if the vehicle speed is below a pre-set value.
When the vacuum solenoid valve is energized it will block vacuum from
reaching the advance unit. When the speed sensor tells the electronic
amplifier that the vehicle is traveling faster than the pre-set speed,
the electronic amplifier will de-energize the vacuum solenoid valve.
This will again allow vacuum to reach the advance unit on the distribu-
tor. With this system spark advance will only be allowed during cruise
conditions and the HC and NO emissions will be reduced.
A
-------
6-44
43. A slightly different hot override switch has been used by
General Motors for thier spark control system. This
switch is called a
44. The inside of the TVS switch is slightly different from
the CTO switch. This switch has a small
instead of a ball in the switch body.
45. ESC stands for
46. The
is the heart
of the ESC system.
TRANSMISSION REGULATED SPARK SYSTEM
The TRS or Transmission Regulated Spark system functions very much like
TRANSMISSION REGULATED SPARK
/X^ IGNITION
/ ^CARBURETOR SW|TCH,
SOLENOID
VACUUM VALVE
TEMPERATURE
SWITCH
TRANSMISSION
SWITCH
^DISTRIBUTOR
FIGURE 6-31
-------
sc
6-45
the ESC system we just discussed. This system, however, uses a trans-
mission switch instead of the speed sensor and electronic amplifier.
Both the transmission switch and the air temperature switch must be
closed to energize the solenoid vacuum valve.
When the solenoid vacuum valve is energized, no vacuum will be allowed
to the advance unit. When the transmission is in any of the lower gears,
it will complete the electrical circuit and energize the vacuum solenoid.
When the transmission shifts into high gear, the transmission switch will
open. This will de-energize the solenoid and allow vacuum advance. The
air temeprature switch will open any time the air is below 50°F. This
will allow vacuum advance until the air temperature increases above 50°F.
Once the air temperature is above 50°F, the transmission switch controls
when advance will be allowed and denied.
SPARK DELAY SYSTEM
The last two spark control systems we will look at are very simple. The
first of these is the spark delay system. As you recall, this system
only has one component. This is the spark delay valve.
The spark delay valve is located in the vacuum line between the carbure-
tor ported vacuum tap and the advance unit on the distributor. You must
remember that this vacuum will drop to 0" Hg every time the throttle
plates close or are fully open. When this vacuum does go to 0", the
vacuum advance will be denied immediately. When the ported vacuum
signal increases again, it will be delayed for a few seconds before it
is allowed to advance the spark. Let's now take a look inside the spark
delay valve and see how it delays this vacuum signal.
Figure 6-32 shows the inside of a spark delay valve. This figure shows
the delay valve with a vacuum condition on the carburetor side of the
valve. When the spark delay valve is in this position the air in the
advance unit and vacuum line will be slowly drawn through the valve.
-------
6-46
TO
CARBURETOR
TO
DISTRIBUTOR
SINTERED METAL RESTRICTOR
FIGURE 6-32
You can see in figure 6-32 a sintered metal restrictor is used in the
delay valve. The air in the distributor advance unit will slowly pass
through the metal restrictor. This is how the vacuum is delayed. It
takes a few seconds for the air to bleed through the restriction.
When the ported vacuum signal drops to 0", air will rush into the
TO
CARBURETOR
TO
DISTRIBUTOR
SINTERED METAL RESTRICTOR
FIGURE 6-33
-------
sc
6-47
carburetor side of the delay valve. This air will unseat the small
rubber check valve inside the delay valve body. This will immediately
remove the vacuum condition in the advance unit. Figure 6-33 shows the
delay valve in this condition.
ORIFICE SPARK ADVANCE CONTROL SYSTEM
Now that you understand how the delay valve spark control system func-
tions, we will look briefly at the last spark control system. This is
the Orifice Spark Advance Control system.
Figure 6-34 shows the OSAC valve and how it is connected to the carbu-
retor and distributor. This valve functions the very same way as the
TO
DISTRIBUTOR
PORTED
VACUUM
OSAC
VALVE
FIGURE 6-34
spark delay valve. It will delay the vacuum signal from reaching the
distributor. It will vent the vacuum from the distributor at the same
time the ported vacuum signal goes to 0" Hg. The OSAC valve may, however,
have a temperature override. If the OSAC valve is so equipped, it will
not delay the vacuum signal if the temperature is below 60°F. It will
not start delaying the vacuum until the air temperature is above 60°F.
-------
6-48
47. TRS stands for
system.
48. The TRS system uses a switch
instead of the speed sensor and electronic amplifier.
49. The valve is the only component in
the spark delay system.
Now you should be familiar with the function of the various spark control
systems and components. It is now time to look at the inspection
procedures for the spark control system.
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sc
6-49
SYSTEM INSPECTION
An inspection of the Spark Control system should be made periodically and
prior to any testing of the system. This inspection will require no tools
and takes only a few minutes. Many problems may be avoided or corrected
by these steps.
1. Obtain a good service manual and see that all components
are properly installed on the engine. Make sure no
modifications have been done to the system or any of its
components. All vacuum and electrical components should
be in place.
In order for the spark control system to operate properly,
all components must be installed on the vehicle.
2. Check the system connecting hoses for cracks, deterioration
and loose connections.
Any air leaks in the hoses will reduce the spark control
system's effectiveness. If any vacuum line is leaking
severely, a lean miss condition may occur.
3. Check the electrical wires in the system for cracks, frays
or other deterioration in the insulation. Also check the
wire connectors for improper fits, dirt and corrosion.
If any shorted, grounded, or open wires are present in the
spark control system, the vehicle will not operate correctly.
Performance, driveability and emissions can all suffer if
poor wiring exists in the system.
A good visual inspection should take only a few minutes. This inspection
can show you where trouble might occur and can solve some problems before
you begin testing the spark control system.
-------
6-50
50. When inspecting the spark control system check the system
connecting for cracks, deterioration and loose
connections.
51. Performance, driveability and can all
suffer if poor wiring exists in the spark control system.
-------
sc
6-51
SYSTEM TESTING
Now that you are familiar with the spark control system, we will look at
some of the test procedures for this system. Since there are many
variations in spark control systems, you must always check the manufac-
turer's recommended test procedures for the specific automobile you are
working with.
When testing the transmission control spark system with an automatic
transmission, it is first necessary to identify if the transmission switch
is installed in the governor oil pressure circuit or connected to the
direct clutch circuit. A good service manual should tell you which method
is used on the car you are working with.
TESTING THE TCS SYSTEM
If the transmission switch is connected to the governor oil pressure
circuit, it will be necessary to do the following:
1. Raise the rear wheels and install safety stands.
2. Install a vacuum gauge in the vacuum hose just before the
vacuum advance unit on the distributor.
3. Start the engine.
4. Put the transmission in drive.
TO IGNITION
SWITCH
FIGURE 6-35
-------
6-52
5. Once the engine coolant has warmed to operating temperature,
maintain speeds of 0-40 MPH.
6. The vacuum gauge should allow ported vacuum as you reach
speeds of approximately 40 MPH.
7. Use a timing light to verify that the vacuum advance unit
is working.
If the transmission switch is installed in the direct clutch circuit on
the automatic transmission, the following is needed to check the
system:
1. Install a vacuum gauge in the vacuum hose, just before the
vacuum advance unit on the distributor.
2. Start the engine.
3. Apply the brakes.
4. Put the transmission in reverse.
5. Once the coolant has reached normal operating temperature,
increase the engine speed to 1500 RPM.
6. At this time, vacuum should be applied to the distributor
advance unit on the distributor.
If the automobile is equipped with a standard transmission, it can be
checked by the following:
1. Bring the engine to normal operating temperature.
2. Connect a vacuum gauge to the vacuum line, just before the
advance unit on the distributor.
3. Apply the brakes.
4. Bring the engine to 1500 RPM.
5. Depress the clutch.
6. Run the transmission through all gears while observing the
vacuum gauge. The vacuum gauge should read "0" in all
low gears. In high gear, carburetor ported vacuum should be
indicated. If for some reason, after the transmission
control spark system has been tested and vacuum was not
applied to the vacuum advance unit on the distributor,
-------
sc
6-53
0 VACUUM
2ND GEAR
1ST GEAR
PORTED VACUUM
3RD GEAR
FIGURE 6-36
it becomes necessary to follow manufacturer's technical or
shop manual for exact procedures for testing individual
components.
52. When testing the transmission control spark system with
an automatic transmission, it is first necessary to iden-
tify if the transmission switch is installed in the
governor oil pressure circuit or connected to the
53. If the transmission switch is connected to the governor
oil pressure circuit, it will be necessary to use a
to verify that the vacuum advance
unit is working.
-------
6-54
TESTING THE ESC SYSTEM
Testing the operation of the ESC system is much like any of the spark
control systems. This system is tested as follows:
1. Jack up the rear wheels and install safety stands.
2. Tee a vacuum gauge into the line just before the distributor
advance unit.
3. Place the transmission in neutral.
4. Speed the-engine to approximately 1500 RPM.
5. With the temperature switch below 50°F, the vacuum gauge
should have a vacuum reading of approximately 6 to 10 inches
of mercury.
6. With the transmission in neutral and ambient air temperature
above 65°F, the vacuum gauge should read "0".
7. Shift the transmission into gear and accelerate slowly to
between approximately 28 to 35 MPH. The vacuum gauge should
read at least 6 inches of vacuum.
30 MPH VACUUM = 6" hg
FIGURE 6-37
8. Start allowing the engine to decelerate. Somewhere between
18 and 15 MPH the vacuum gauge reading should drop to 0.
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sc
6-55
DECELERATE TO 15 MPH VACUUM * 0
FIGURE 6-38
This is an operational procedure test and it is important
to check the manufacturer's technical or shop manual for
exact procedures for each make and model of automobile.
SPARK DELAY VALVE TEST
When testing a spark delay valve with a hand vacuum pump, connect the
pump to the black side of the valve. You should be able to pump up
TESTING SPARK DELAY VALVE
FIGURE 6-39
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6-56
TESTING SPARK DELAY VALVE
FIGURE 6-40
vacuum and the gauge will slowly drop to 0. If the gauge does not drop
to 0, the valve is plugged. When the hand pump is connected to the
colored side of the spark delay valve, no vacuum can be pumped. If
vacuum can be pumped, the valve is not working correctly.
OSAC VALVE TEST
In testing the OSAC valve, all that is necessary to do is to bring the
FIGURE 6-41
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sc
6-57
engine to curb idle and have an outside temperature of approximately 60°F
or more. Check to make sure that vacuum is being applied to the OSAC
valve and install a vacuum gauge in the hose from the OSAC valve to the
distributor. Increase the engine speed to approximately 2000 RPM and
hold it there. The vacuum gauge should rise slowly to the maximum vacuum
in a few seconds. If no vacuum shows on the vacuum gauge after approxi-
mately 17 seconds, this shows that the OSAC valve is defective. Also, it
should be noted, that the vacuum should increase slowly proving that the
valve is working correctly.
54. When testing a spark delay valve with a hand vacuum pump,
connect the pump to the black side of the valve. You
will be able to pump up vacuum and the gauge will
to 0.
55. In testing the OSAC valve, when the engine is accelerated
to 2000 RPM, vacuum to the distributor should be delayed
for about seconds.
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sc
6-59
SYSTEM SUMMARY
PURPOSE
The purpose of the spark control system is to control the advance and
retard of the ignition spark to improve combustidn and reduce the forma-
tion of hydrocarbons (HC) and oxides of nitrogen (NO ) during varying
X
engine operations.
MAIN COMPONENTS
Coolant Temperature Switch - Senses cooling system temperature and allows
vacuum advance only when the engine is cold.
Hot Override Switch - Senses cooling system temperature and allows full
vacuum when the engine starts to overheat.
Transmission Switch - Prevents vacuum advance in all gears except high
gear.
Vacuum Advance Solenoid Valve - A two-position valve allowing vacuum to
reach the distributor advance unit or venting air preventing vacuum advance
SYSTEM FUNCTION
The spark control system operates to allow vacuum advance when the coolant
temperature is cold, or when the transmission is in high gear. At other
times, the spark is in retard position which increases exhaust gas tempera-
ture, promoting additional burning of hydrocarbons (HC) in the exhaust
manifold. Retarded spark will also lower peak combustion temperature (by
igniting spark later in the cycle) thereby reducing oxides of nitrogen
(NO ) formation.
A
Some manufacturers use the following individual components on certain
engines to control spark advance.
Orifice Spark Advance Control (OSAC) - This system is now used on all
Chrysler products. Its function is to delay vacuum advance for approxi-
mately 30-45 seconds under normal engine temperatures. When the engine
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6-60
air cleaner temperature is below 50°F, vacuum will flow through the valve
unrestricted. The valve is mounted in the air cleaner assembly.
Spark Delays - Ford has used a number of spark delay valves operating
similar to Chrysler's OSAC valve. This delay serves to lower HC emissions
by not allowing full vacuum advance until the vehicle has been cruising
for 7-20 seconds. The spark delays used by Ford do not contain a cold
engine by-pass system. The spark delay valves are normally found mounted
in the vacuum line near the distributor.
Electronic Spark Control (ESC) - Operates similar to the transmission
switch discussed in the main components of the spark comtrol system.
However, the ESC uses an electrical signal from a temperature switch
mounted in the left front door pillar in some 71-73 Fords to activate an
amplifier which in turn supplies the signal to the vacuum advance.
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ANSWERS
sc
6-61
1. oxides of nitrogen
2. combustion process
3. hydrocarbon emissions
4. exhaust manifold
5. heavy load
6. ignition timing
7. piston
8. exhaust gas
9. advanced ignition
10. vacuum solenoid
11. electrical circuit
12. transmission
13. first and second
14. vacuum solenoid
15. cold temperature override
16. manifold vacuum
17. hot override
18. Electronic Spark
19. accelerating
20. voltage signal
21. electronic amplifier's
22. Transmission Regulated Spark
23. transmission
24. spark delay
25. delay valve
26. orifice spark advance control
27. distributor advance or
vacuum advance
28. wire coil
29. electrical terminals or
hose connections
30. magnetic field
31. current
32. ignition switch
33. series
34. transmission
35. hydraulic pressure
36. linkage
37. de-energized
38. engine coolant
39. heat sensitive
40. upper portion or upper p
41. intake manifold
42. hot override
43. thermal vacuum switch
44. piston
45. Electronic Spark Control
46. electronic amplifier
47. Transmission Regulated Sp
48. transmission
49. spark delay
50. hoses
51. emissions
52. direct clutch circuit
53. timing light
54. slowly drop
55. 17
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1 REPORT NO.
EPA-450/3-77-041
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AMD SUBTITLE 5. REPORT DATE
Motor Vehicle Emissions Control - Book Six November 1977
Spark Control Systems
7. AUTHORtS)
B.D. Hayes
M.T. Maness
R.A. Ragazzi
R.A. Barrett
9, PERFORMING ORGANIZATION NAME AND ADDRESS
Department of Industrial Sciences
Colorado State University
Fort Collins, Colorado 80523
12. SPONSORING AGENCY NAME AND ADDRESS
Control Programs Development Division
Office of Air Quality Planning and Standar
Office of Air and Waste Management
U.S. Environmental Protection Agency
15. SUPPLEMENTARY NOTES Research Triangle Park,
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
T008135-01-0
T900621-01-0
13. TYPE OF REPORT AND PERIOD COVERED
Final Report
jg 14. SPONSORING AGENCY CODE
EPA 200/04
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 Spark Control Systems which are an
integral part of automobiles today. The mechanic's increased knowledge 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.
17.
KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
Air Pollution Exhaust Manifold
Spark Control Systems Ignition Timing
Photochemical Vacuum Solenoid
System Inspection Manifold Vacuum
Hydrocarbons Electronic Spark
Carbon Monoxide Thermal Vacuum
Oxides of Nitrogen Switch
13. DISTRIBUTION STATEMENT
Release Unlimited
b.IDENTIFIERS/OPEIM ENDED TERMS
19. SECURITY CLASS (This Report)
Unclassified
20. SECURITY CLASS (This page)
Unclassified
c. COSATI Field/Group
21. NO. OF PAGES
69
22. PRICE
EPA Form 2220-1 (9-73)
. GOVERNMENT PRINTING OFFICE: 1978-745-
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