spark control system.pdf

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SPARK CONTROL SYSTEM
1988 Jeep Cherokee
1988 Exhaust Emission Systems
JEEP SPARK CONTROL SYSTEMS
DESCRIPTION
Jeep vehicles use spark control devices to assist ignition
system in controlling exhaust emissions. They are Spark Control
Temperature Override (CTO) valve, Non-Linear Vacuum Regulator (NLVR)
valve, Forward Delay Valve, Reverse Delay Valve and on 4-cylinder
engines, Vacuum Spark Control Delay Valve. System application depends
upon engine size, emissions category and vehicle model.
COOLANT TEMPERATURE SENSOR (CTS)
The coolant temperature sensor is located in the intake
manifold coolant jacket. This sensor provides a voltage signal to the
Electronic Control Unit (ECU). The ECU uses this signal to determine
engine temperature. During cold engine operation, the ECU responds by
increasing ignition advance and inhibiting EGR operation.
NON-LINEAR VACUUM REGULATOR VALVE (NLVR)
NLVR valve is used on carbureted 6.0L models. This valve
supplies vacuum advance unit with a regulated combination of manifold
and carburetor ported vacuum when engine load is low and switches to
supply only carburetor ported vacuum as load increases.
Fig. 1: Non-Linear Vacuum Regulator Valve
Courtesy of Chrysler Motors.
OPERATION
NON-LINEAR VACUUM REGULATOR VALVE
There are 2 input ports on NLVR: intake manifold vacuum and
carburetor ported vacuum. One outlet port connects to distributor
vacuum unit. At curb idle, regulated vacuum is supplied to advance
unit, when manifold vacuum is high and ported vacuum is very low. See
Fig. 1.
NLVR regulates vacuum signal so it is between these 2 vacuum
source levels at idle. As engine load increases and vacuum signal is
above 7.5 in. Hg vacuum, regulator valve switches to ported vacuum
output.
FORWARD DELAY VALVE
Some engines use this valve to improve driveability and
reduce hydrocarbon emissions. Valve functions to delay effects of
sudden increases in vacuum. This prevents sudden spark advance during
deceleration.
REVERSE DELAY VALVE
Some engines use this valve to improve cold driveability and
reduce hydrocarbon emissions. Valve is installed in vacuum line to
delay effects of manifold vacuum decrease causing retarded ignition
timing.
VACUUM ADVANCE COOLANT TEMPERATURE OVERRIDE (VA-CTO)
This valve is used on carbureted 6.0L engines to improve
driveability when engine is cold. It is located in vacuum advance
circuit. When vacuum is greater at port "4" than at port "1", air
must flow through orifice to equalize pressure. This creates
momentary delay that prevents sudden decrease in spark advance. When
vacuum is greater at port "1" than at port "4", air flows freely
through check valve and pressure is instantly equalized.
TESTING
NON-LINEAR VACUUM REGULATOR VALVE (NLVR)
Connect vacuum gauge to distributor port "DIST" on NLVR.
With engine at idle speed, a vacuum reading of 7 in. Hg vacuum should
be shown. As throttle is opened and engine speed increases, ported
vacuum level should be indicated. If not, replace NLVR. See Fig. 1.
FORWARD DELAY VALVE
1) Connect external vacuum source to port on Black (or Red)
side of delay valve. Connect vacuum gauge to port on colored side of
valve.
2) Apply a constant 10 in. Hg vacuum. Note time required for
gauge pointer to move from 0-8 in. Hg.
3) If valve fails to meet time limits, replace valve. If
valve meets specifications, install so that Black (or Red) side is
toward vacuum source.
FORWARD DELAY VALVE TIME LIMITS
Valve Color
(1)
Min. Time
Max Time
                                                                                                               
¡¡¡¡¡¡¡¡¡¡¡¡¡ ¡¡¡ ¡¡¡ ¡¡¡¡ ¡¡¡ ¡¡¡ ¡¡ ¡¡ ¡¡¡ ¡¡¡ ¡¡¡ ¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡ ¡¡¡ ¡¡¡¡¡¡ 
Black/Purple .................
Black/Gray ....................
Black/Brown ..................
Black/Orange .................
Black/White ..................
Black/Yellow .................
Black/Green ..................
(1) - Time in seconds.
3.2
8
16
1.5
50
80
160
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4.8
12
24
2.5
77
120
240
1) Connect external vacuum source to port on White side of
delay valve. Connect vacuum gauge to port on colored (non-White) side
of valve.
2) Apply a constant 10 in. Hg vacuum, note time required for
gauge pointer to move from 0-8 in. Hg.
3) If valve fails to meet time limits, replace valve. If
valve meets specifications, install with non-White side toward vacuum
source.
REVERSE DELAY VALVE TIME LIMITS
Valve Color
(1)
Min. Time
3.2
8
12
16
80
300
1.5
Max. Time
4.8
12
18
24
120
450
2.5
White/Purple .................
White/Gray ....................
White/Gold ...................
White/Brown ..................
White/Yellow .................
White/Red ....................
White/Orange .................
(1) - Time in seconds.
1) Connect "T" fitting at ports "1" and "4". Connect vacuum
gauge to each fitting. Start engine. Vacuum should be equal at both
ports. See Fig. 2.
2) When throttle is suddenly depressed, vacuum at port "1"
will instantly decrease and vacuum at port "4" should be maintained
momentarily. If valve fails these tests, replace valve.
Fig. 2: Vacuum Spark Control Delay Valve
Courtesy of Chrysler Motors.
                                                                                                               
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REVERSE DELAY VALVE
                                                                                                               
¡¡¡¡¡¡¡¡¡¡¡¡¡ ¡¡¡ ¡¡¡ ¡¡¡¡ ¡¡¡ ¡¡¡ ¡¡ ¡¡ ¡¡¡ ¡¡¡ ¡¡¡ ¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡ ¡¡¡ ¡¡¡¡¡¡ 
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VACUUM SPARK CONTROL DELAY VALVE

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