1988 JEEP CHEROKEE Service Repair Manual

Fig. 3: Dash Gauges & Warning Lights (Turbo-Diesel Engines)
Courtesy of Chrysler Motors.

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97I0 02000: S H IF T IN TE R LO CK

1988 J e ep C hero ke e
NHTSA RECALL BULLETIN
Model(s): 1984-95 Jeep Cherokee
1993-95 Jeep Grand Cherokee
Campaign No: 97I002000
Number of Affected Vehicles: 2200000
Beginning Date of Manufacture: 1983 AUG
Ending Date of Manufacture: 1995 JUL
VEHICLE DESCRIPTION:
Multipurpose passenger vehicles equipped with automatic transmissions.
DESCRIPTION OF DEFECT:
This is not a safety recall in accordance with Federal Regulation 573.
However, it is deemed a safety improvement campaign by the agency.
Drivers can mistakenly step on the accelerator pedal when they intend
to step on the brake pedal.
CONSEQUENCE OF DEFECT:
Pedal misapplication by a driver can cause unintended acceleration.
CORRECTIVE ACTION
Dealers will install a shift interlock on the automatic transmission
of these vehicles.
Chrysler has decided to conduct a safety improvement campaign to
install a shift interlock on these vehicles. Owners can contact
Chrysler at 1-800-853-1403.
ADDITIONAL INFORMATION:
The National Highway Traffic Safety Administration operates Monday
through Friday from 8:00 AM to 4:00 PM, Eastern Time. For more
information call (800) 424-9393 or (202) 366-0123. For the hearing
impaired, call (800) 424-9153.

SPA R K C O NTR O L S YSTE M

1988 J e ep C hero ke e
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 (1)









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Valve Color Min. Time Max Time

Black/Purple ................. 3.2 ........................... 4.8
Black/Gray .................... 8 ............................. 12
Black/Brown .................. 16 ............................. 24
Black/Orange ................. 1.5 ........................... 2.5
Black/White .................. 50 ............................. 77
Black/Yellow ................. 80 ............................ 120
Black/Green .................. 160 ........................... 240
(1) - Time in seconds.









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REVERSE DELAY VALVE
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 (1)









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Valve Color Min. Time Max. Time
White/Purple ................. 3.2 ........................... 4.8
White/Gray .................... 8 ............................. 12
White/Gold ................... 12 ............................. 18
White/Brown .................. 16 ............................. 24
White/Yellow ................. 80 ............................ 120
White/Red .................... 300 ........................... 450
White/Orange ................. 1.5 ........................... 2.5
(1) - Time in seconds.









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VACUUM SPARK CONTROL DELAY VALVE
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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STA R TE R - B O SC H/M IT S U BIS H I

1 988 J e ep C hero ke e
1988 Starters
BOSCH & MITSUBISHI
Jeep with 4.0L 6-Cyl.
DESCRIPTION
NOTE: Information on Jeep 2.5L starter not available from
manufacturer.
Bosch and Mitsubishi use a permanent magnet starter. A
planetary gear train transmits power between starter motor and pinion
shaft. The starter magnetic field is produced by 6 permanent magnets.
The Mitsubishi starter is a 12-volt unit that has the solenoid mounted
on the starter housing. See Fig. 3.
TROUBLE SHOOTING
NOTE: See the TROUBLE SHOOTING - BASIC PROCEDURES article
in the GENERAL TROUBLE SHOOTING section.
TESTING (ON VEHICLE)
AMPERAGE DRAW TEST
NOTE: Engine should be at operating temperature before performing
this test. Heavy duty oil or a tight engine will increase
starter draw amperage. Tests are performed with standard
volt-ammeter tester.
1) Connect tester and remote starter switch. Set voltmeter
selector to 16-volt position. Select function to 0-500-amp scale.
Connect voltmeter leads to corresponding polarity battery terminals.
2) Connect ammeter leads to corresponding battery terminals.
Disconnect coil wire from distributor cap and attach to ground to
prevent engine from starting.
3) Crank engine and observe exact reading on voltmeter. Stop
cranking engine. Turn tester control knob clockwise until voltmeter
reads exactly the same as when engine was cranked with remote starter
switch. Ammeter should indicate starter draw of about 150-220 amps.
STARTER RESISTANCE TEST
Use a voltmeter that will indicate tenths of a volt. Without
disconnecting any starter connections, perform the following
resistance tests:
1) Perform following tests with engine cranking and all
terminals connected. Connect a voltmeter at following locations:
* Positive lead to battery positive post and negative lead
to battery terminal on starter.
* Positive lead to starter housing and negative lead to
negative post on battery.
* Positive lead to battery negative post and negative lead
to battery cable connector on engine block.
2) Each of these 3 connections should show a voltmeter

reading of .2 volt or less. If reading exceeds .2 volt, clean or
repair cables and connections in circuit. Connect a voltmeter at
following locations:
* Positive lead to battery positive post and negative lead
to cable clamp.
* Positive lead to battery negative post and negative lead
to cable clamp.
3) If reading is other than zero on voltmeter, clean or
repair cables and connections in circuit. Connect a voltmeter at
following location:
* Positive lead to battery positive post and negative lead
to starter solenoid lead to the field coils.
4) If reading exceeds .3 volt, clean or repair cables and
connections in circuit.
SOLENOID TEST
1) Connect a heavy jumper wire on starter relay between
battery and solenoid terminals. If engine cranks, solenoid is okay. Go
to RELAY TEST .
2) If engine does not crank, check wiring and connections
from relay to starter. Repair or replace as necessary. If engine still
fails to crank, starter is defective.
RELAY TEST
1) On automatic transmission/transaxle vehicles, put gear
selector in "NEUTRAL" or "PARK". On manual transmission/transaxle
vehicles, put gear selector in "NEUTRAL". Set parking brake and block
wheels. DO NOT remove relay connector. Using a 12-volt test light,
check for battery voltage between starter relay battery terminal and
ground.
2) Use a jumper wire on starter relay between battery and
ignition terminals. If engine cranks starter relay is good. If starter
does not crank go to next step.
3) Connect another jumper wire to starter relay between
ground terminal and ground. Repeat above test. If engine cranks,
starter relay is good. Inspect transmission linkage for improper
adjustment (automatic transmission), defective neutral safety switch
(automatic transmission) or poor ground connection between relay
housing and mounting surface.
TESTING (ON BENCH)
STARTER SOLENOID
1) With starter removed, disconnect field coil wire from
field coil terminal on starter. Using an ohmmeter, check for
continuity between solenoid and field coil terminals.
2) Check for continuity between solenoid terminal solenoid
housing. Continuity should be present in both tests. If continuity is
present, solenoid is good. If no continuity is present, replace
solenoid. Reconnect field coil wire to field coil terminal.
ARMATURE FOR SHORT CIRCUIT
Place armature in a growler and hold a thin steel blade
parallel 3/16" above core while rotating armature slowly. If armature

is shorted, blade will vibrate and be attracted to core. Replace
shorted armature.
ARMATURE FOR GROUND
Using a self-powered test light and touch one lead to
armature shaft and other lead to each commutator bar. See Fig. 1. If
light glows, armature is grounded and should be replaced.
Fig. 1: Testing Starter Armature for Ground
FIELD COILS FOR GROUND
Using a self-powered test light and touch one probe to series
field coil lead and other probe to field frame. If light glows,
replace field coil housing assembly.
DRIVE CLUTCH UNIT
While holding clutch housing, rotate pinion. Drive pinion
should rotate smoothly in one direction only (should not rotate in
opposite direction). If drive unit does not operate properly, or if
pinion is worn or burred, replace drive unit.