reset JEEP CHEROKEE 1988 Service Repair Manual

guide, adjuster screw assembly, parking brake lever and lever pivot
pin with molybdenum disulphide grease.
2) Connect parking brake lever to secondary brake shoe with
washer and "U" clip. Crimp ends of clip to secure clip on pivot.
Remove wheel cylinder clamp. Position brake shoes on brake support
plate and install hold-down springs.
3) Install parking brake lever strut and spring. Install
adjuster cable guide plate and adjuster cable on anchor pin. Install
primary return spring. Install guide to secondary brake shoe. Install
secondary return spring.
4) Install adjuster screw, spring and lever. Connect lever to
cable. Using Brake Gauge (J-21177-01), preset brake shoe adjustment.
Install brake drums. Adjust brake shoes with drum in place.
5) Install wheels and lower vehicle. To adjust and balance
brake system, apply and release brakes 10-15 times while driving
forward and backward. Road test vehicle.
DRUM BRAKE SHOES - GRAND WAGONEER
Removal
1) Raise vehicle and support with safety stands. Remove
wheels. On models with full-floating rear axle, remove 2 screws that
retain drum on hub.
2) On all models, remove primary shoe return spring,
automatic adjuster actuator spring and secondary shoe return spring.
Remove hold-down springs. Remove brake shoe assemblies. See Fig. 10.
3) Disengage parking brake cable from parking brake lever.
Remove parking brake strut and brake shoe assembly as a unit. Place
wheel cylinder clamps over cylinders in order to retain pistons.
4) Inspect automatic adjuster lever and pivot, actuating
lever, parking brake lever, automatic adjuster and springs. Replace
weak springs, bent levers and parts that are worn or broken.
Fig. 10: Exploded View of Drum Brake Assembly (Grand Wagoneer)
Courtesy of American Motors/Jeep Corp.
Installation
1) Clean support plate. Apply a thin film of molybdenum

CRUIS E C O NTR O L S YSTE M

1988 J e ep C hero ke e
1988 Cruise Control Systems
JEEP CRUISE COMMAND
All Models
DESCRIPTION & OPERATION
Jeep vehicles use an electro-mechanical servo system. The
system consists of a control module, speed sensor, servo, control
switch assembly, vacuum storage canister, check valve and release
system. Release system consists of a mechanical vacuum vent valve and
brake and clutch (M/T) release switches.
Cruise control switch is an integral part of turn signal
switch lever and consists of 2 separate switches. First is an "ON-OFF"
and "RESUME" slide switch located on flat of directional switch lever.
Second is "SET/COAST" push button switch located at end of
directional switch lever. To engage system, move slide switch to "ON"
position and accelerate to desired speed. Depress and release
"SET/COAST" button on end of switch lever. System will now maintain
selected speed.
System will automatically disengage when brake or clutch
pedal is depressed. It can be re-engaged to previously selected speed
by accelerating to 30 MPH and moving slide switch to "RESUME"
position, then releasing switch.
NOTE: When slide switch is moved to "OFF" position, pre-set speed
of "RESUME" function is canceled from memory and must be
reset when system is reactivated.
Higher speed can be set by pressing on accelerator pedal
until new speed is reached and then pushing "SET/COAST" button. Lower
speed can be obtained by lightly depressing brake pedal, allowing the
vehicle to slow to desired speed and then depressing and releasing
"SET/COAST" button.
CONTROL MODULE
Control module receives input voltage representing vehicle
speed from speed sensor, which is driven by the speedometer cable.
Control module has a low speed circuit that prevents operation at
speeds below 30 MPH. See Fig. 1.
SERVO
Servo is controlled by control module and uses manifold
vacuum to control throttle. Bead-link chain connects servo cable to
throttle linkage. See Fig. 1.
CONTROL SWITCH
Control switch assembly is an integral part of turn signal
switch lever. See Fig. 1.
RELEASE SYSTEM
Release system deactivates cruise control system when brake
or clutch pedal is depressed. Either servo vent valve or mechanical
vacuum vent switch admits atmospheric pressure into servo when brake
pedal is depressed.

SYSTEM WILL NOT ENGAGE
Restricted vacuum hose or no vacuum. Control switch or
control module defective. Speed sensor defective. Clutch or brake
light switch defective or misadjusted. Brake light switch wire
disconnected. Open circuit between brake light switch and brake
lights.
RESUME FEATURE INOPERATIVE
Defective servo ground connection. Defective control switch.
ACCELERATE FUNCTION INOPERATIVE
Accelerate circuit in control module inoperative. Defective
control switch.
SYSTEM RE-ENGAGES WHEN BRAKE PEDAL IS RELEASED
Defective control module. Mechanical vent valve not opening.
Kink in mechanical vent valve hose. Brake light switch defective.
CARBURETOR THROTTLE DOES NOT RETURN TO IDLE POSITION
Improper linkage adjustment.
ROAD SPEED CHANGES 2 MPH OR MORE WHEN SETTING SPEED
Centering adjustment wrong. Servo link misadjusted.
ENGINE ACCELERATES WHEN STARTED
Improper servo chain adjustment. Vacuum hose connections
reversed at servo. Defective servo.
SYSTEM DISENGAGES ON LEVEL ROAD WITHOUT APPLYING BRAKES
Loose wire connection. Loose vacuum hose connection. Servo
linkage broken. Defective brake light switch.
ERRATIC OPERATION
Reverse polarity of system wiring. Defective servo. Defective
control module.
VEHICLE CONTINUES TO ACCELERATE WHEN "SET" BUTTON IS RELEASED
Servo or control module defective.
SYSTEM ENGAGES BUT SLOWLY LOSES SET SPEED
Air leak at connections or in vacuum hoses. Air leak on vent
valve on brake pedal.
ADJUSTMENTS
CONTROL MODULE ADJUSTMENT
NOTE: Control module adjustments are preset by manufacturer. If
other components in system appear to be functioning properly

lubricant to axle flange bearing bore and install axle.
YOKE & PINION OIL SEAL
Removal
1) Raise and support vehicle. Remove wheels and brake drums.
Mark and remove drive shaft. Using an INCH lb. torque wrench, record
torque required to rotate pinion several revolutions.
2) Hold yoke from turning and remove pinion nut. Mark drive
pinion shaft and yoke for reassembly reference. Remove yoke and pinion
oil seal.
Installation
1) Coat new seal with rear axle lubricant and install. Align
marks made at disassembly and install yoke. Install new pinion nut and
tighten just enough to remove end play.
CAUTION: DO NOT overtighten pinion nut. If desired preload is
exceeded, a new collapsible pinion spacer sleeve must be
installed and drive pinion preload reset.
2) Using an INCH lb. torque wrench, check torque required to
turn pinion. Refer to torque reading recorded during disassembly and
add 5 INCH lbs. (.6 N.m) for correct preload. Tighten pinion nut
slightly and recheck preload. Repeat procedure until desired preload
is obtained.
REAR AXLE ASSEMBLY
Removal
1) Raise and support vehicle. Remove wheels and brake drums.
Disconnect brake hose-to-axle connection and plug line.
2) Disconnect parking brake cable at brake equalizer. Mark
and remove drive shaft. Disconnect track bar at axle bracket (if
equipped). Remove axle vent tube at axle. Support axle assembly.
Remove spring "U" bolts and tie plates.
3) Loosen, but do not remove, bolts which attach front of
rear spring to frame brackets. Lift axle to relieve axle weight from
springs and remove bolts retaining springs to shackles. Lower springs
to floor. Lower jack and remove axle assembly.
NOTE: Factory axles are shipped without lubricant. When adding
lubricant, position axle horizontally with yoke end of
pinion housing facing downward. Turn pinion shaft several
times to lubricate bearings.
Installation
1) To install, support axle assembly with jack and slide axle
into place. Raise, align and install spring-to-frame and shackle
bolts. Tighten spring-to-frame and shackle bolts to 111 ft. lbs. (150
N.m). Install brake hose, axle vent tube and parking brake cable.
Align and connect drive shaft.
2) Bleed hydraulic system and adjust parking brake cable.
Ensure axle is filled with 75-90W gear lubricant. Ensure spring
centering bolt heads are seated in axle spring seat before tightening
"U" bolts.
OVERHAUL
DISASSEMBLY
NOTE: It is not necessary to remove axle assembly from vehicle to

2) Slowly tighten pinion nut until torque required to rotate
pinion gear is 15-25 INCH lbs. (2-3 N.m). Check torque frequently and
only tighten nut in small amounts.
CAUTION: DO NOT overtighten pinion nut. If preload torque is
exceeded, collapsible spacer must be replaced and preload
reset.
DIFFERENTIAL BEARING END PLAY
1) Place bearing cup over each differential bearing. Install
differential case assembly (without drive gear) in axle housing. On
standard drive axles, install a .142" (3.60 mm) shim on each side of
differential bearing cup and housing. On heavy duty drive axles,
install a .080" (2.03 mm) shim on each side of differential bearing
cup and housing.
2) Install bearing caps and tighten bolts finger tight. Mount
dial indicator to housing so indicator button touches ring gear face
of differential case. Prying between shims and housing, move assembly
to one side. Zero dial indicator, then pry assembly to opposite side.
Read and record indicator reading. DO NOT zero or read indicator while
prying.
3) Amount read on indicator is shim thickness which must be
added in order to arrive at a no preload or end play condition. Shims
are available in thicknesses of .142" (3.60 mm) to .174" (4.41 mm) i\
n
.002" (.050 mm) increments.
4) When all side play is eliminated, check drive gear face of
case for runout. Runout should not exceed .002" (.050 mm). Remove case\
from housing and retain shims used to eliminate side play. See Fig. 5.
Fig. 5: Differential Bearing End Play & Runout Measurement
RING GEAR BACKLASH ADJUSTMENT
1) Install differential and ring gear assembly in housing

EG R S YSTE M

1988 J e ep C hero ke e
1983-88 Exhaust Emission Systems
JEEP EXHAUST GAS RECIRCULATION
DESCRIPTION
Purpose of the Exhaust Gas Recirculation (EGR) system is to
limit formation of oxides of nitrogen (NOx) emissions. This is done by\
reducing high peak combustion temperatures at which NOx is formed. By
reintroducing some exhaust gas back into combustion chamber, high
temperatures are avoided. Thus NOx emissions formation is reduced.
System consists of vacuum-operated EGR valve and coolant
temperature override (CTO) switch. In addition, some models are
equipped with air cleaner-mounted thermal vacuum switch (TVS), and
some are equipped with an EGR vacuum dump valve.
OPERATION
When the EGR valve receives vacuum signal, through the CTO
switch, EGR valve opens and meters gases from exhaust manifold into
intake manifold. Individual component operation is as follows:
EGR VALVE
EGR valve is mounted on intake manifold. Exhaust gas is drawn
from exhaust crossover passage or exhaust manifold. Two types of EGR
valves are used: valve without backpressure sensor and valve with
integral backpressure sensor.
EGR Valve W/O Integral Backpressure Sensor
EGR valves are calibrated by use of different shapes of valve
pintles or orifices. Valve is normally held closed by spring (above
diaphragm). Valve opens by overcoming spring tension when vacuum is
sensed through coolant temperature override switch (CTO) and
backpressure sensor (if equipped).
EGR Valve W/Integral Backpressure Sensor
Calibration is accomplished by use of different diaphragm
spring loads and flow control orifices. This integral type unit
combines EGR valve and backpressure sensor functions into one
component. Restrictor plate is required with some engines.
Exhaust gas exerts backpressure inside exhaust manifold
whenever engine is running. This pressure is conducted through hollow
pintle stem into EGR diaphragm control chamber. If this pressure is
great enough to overcome spring tension against diaphragm, diaphragm
is moved against bleed valve and exhaust gas flow begins.
COOLANT TEMPERATURE OVERRIDE (CTO) SWITCH
Coolant temperature override (CTO) switch is located in
coolant passage at cylinder head or coolant passage at intake
manifold.
Inner port of switch is connected to EGR port on intake
manifold and outer port is connected to EGR valve, or EGR-TVS. Switch
opens at a preset temperature. Below these temperatures, no EGR is
possible.

Fig. 1: Jeep V8 Carbureted Engine EGR System
Courtesy of Chrysler Motors.
THERMAL VACUUM SWITCH (TVS)
Used only on carbureted 6-cylinder and V8 engines, this
switch is located in air cleaner and acts as on-off switch for EGR
system. It is controlled by ambient temperature in air cleaner. Switch
controls vacuum passage between CTO switch and EGR valve. Below preset
temperature, TVS blocks passage of vacuum delaying EGR operation and
improving cold driveability.

If equipped, the EMR light (some models may use a reminder
flag) reminds vehicle operator that an emission system maintenance is
required. This indicator is activated after a predetermined
time/mileage.
When performing a smog check inspection, ensure EMR indicator
is not activated. On models using an EMR light, light should glow when
ignition switch is turned to ON position and should turn off when
engine is running.
If an EMR flag is present or an EMR light stays on with
engine running, fail vehicle and service or replace applicable
emission-related components. To reset an EMR indicator, refer to
appropriate MAINTENANCE REMINDER LIGHTS in the MAINTENANCE section.
MALFUNCTION INDICATOR LIGHT (MIL)
The Malfunction Indicator Light (MIL) is used to alert
vehicle operator that the computerized engine control system has
detected a malfunction (when it stays on all the time with engine
running). On some models, the MIL may also be used to display trouble
codes.
As a bulb and system check, malfunction indicator light will
glow when ignition switch is turned to ON position and engine is not
running. When engine is started, light should go out.

mounted on throttle body and senses angle of throttle blade opening.
A voltage signal of up to 5 volts at wide open throttle is
produced by TPS. Voltage varies with throttle angle changes. This
signal is transmitted to ECU where it is used to adjust air/fuel
ratio during acceleration, deceleration, idle, and wide open throttle
conditions.
A dual TPS is used on models with automatic transmissions.
This dual TPS not only provides ECU with input voltages but also
supplies automatic transmission control unit with input signals
relative to throttle position.
Knock Sensor
Knock sensor (detonation sensor) is located on lower left
side of cylinder block just above oil pan. Knock sensor picks up
detonation vibration from engine and converts it to an electrical
signal for use by ECU.
ECU uses this information to determine when a change in
ignition timing is required. Knock sensor allows for engine operation
on either "premium" unleaded or "regular" unleaded fuel.
When knock occurs, ECU retards ignition timing in one or
more cylinders until detonation is eliminated.
Speed Sensor
Speed sensor is secured by special shouldered bolts to
flywheel/drive plate housing. Speed sensor is nonadjustable and
preset at factory. Speed sensor senses TDC and engine speed by
detecting flywheel teeth as they pass pick-up coil during engine
operation. See Fig. 2.
Flywheel has a large trigger tooth and notch located 12
small teeth before each TDC position. When a small tooth and notch
pass the magnetic core in sensor, concentration and collapse of the
magnetic field created induces a small voltage spike into sensor
pick-up coil windings. These small voltage spikes are sent to ECU,
allowing ECU to count the teeth as they pass sensor.
When a large tooth and notch pass magnetic core in sensor,
increased concentration and collapse of the magnetic field induces a
higher voltage spike than smaller teeth. Higher spike indicates to
ECU that a piston will soon be at TDC position, 12 teeth later.
Ignition timing for cylinder is either advanced or retarded by ECU
based upon "sensor input".
Fig. 2: Speed Sensor Operation
Courtesy of Chrysler Motors.
Engine Switches
Several switches provide operating information to ECU. These

MAIN TE N AN CE R EM IN DER L IG HT R ESET P R O CED URES

1988 J e ep C hero ke e
1988-92 MAINTENANCE
Chrysler Motors Maintenance Reminder Lights
Jeep; Cherokee, Comanche, Wagoneer (1988-90), Wrangler
EMISSION MAINTENANCE INDICATOR LIGHT (1988-90)
Vehicles are equipped with an emission maintenance indicator
light on instrument cluster. This light will come on one time at 82,
500 miles to alert driver that emission service is required. At this
time, oxygen sensor and PCV valve must be replaced and all other
emission components should be inspected and serviced or replaced as
necessary.
Indicator timer is located under dash, near accelerator pedal
or to right of steering column. Timer cannot be reset. To turn off
light, timer must be replaced or disconnected. Since timer and sensor
are interdependent, if timer should fail prematurely, oxygen sensor
should be replaced at same time to preserve correct replacement
interval.
To replace timer on Cherokee, Comanche and Wagoneer models,
remove cruise control module (if equipped). Remove timer mounting
screws. Disconnect electrical connector. On Wrangler models, remove
timer mounting screws. Disconnect electrical connector. On all models,
install remaining components.
EMISSION MAINTENANCE INDICATOR LIGHT (1991-92)
Vehicles are equipped with an emission maintenance indicator
light on instrument cluster. This light will come on one time at 82,
500 miles to alert driver that emission service is required. At this
time, oxygen sensor must be replaced and all other emission components
should be inspected and serviced or replaced as necessary. Chrysler's
Diagnostic Readout Box (DRB-II) tester is required to reset the
emission maintenance indicator light.
Reset Procedure
Using DRB-II tester, access SELECT SYSTEMS. Select
appropriate engine. Select with or without A/C. Select FUEL &
IGNITION. Select ADJUSTMENTS. Select RESET EMR LIGHT. Reset EMR light.
When DRB-II is finished resetting light, DRB-II display will read EMR
LIGHT IS RESET.