1988 JEEP CHEROKEE check engine light

Crankshaft End Play
1) Using dial indicator, check crankshaft end play. Inspect
crankshaft thrust surfaces or thrust bearing for wear if not within
specification. See ENGINE SPECIFICATIONS table.
2) Replace thrust bearing if required. When replacing thrust
bearing, pry crankshaft forward then reward prior to tightening main
bearing cap to specification. Recheck end play. Replace crankshaft if
not within specification.
REAR MAIN OIL SEAL
Removal
1) Remove oil pan. See OIL PAN REMOVAL in this section.
Remove rear main bearing cap. Note direction of seal lip installation.
Remove seal from bearing cap. Loosen all remaining main bearing cap
bolts.
2) Using a brass drift, tap upper seal around crankshaft
until seal protrudes enough to permit removal with pliers. Remove
seal.
Installation
1) Clean crankshaft seal surface. Coat seal-to-block contact
areas with liquid soap. Lightly coat all seal lips with engine oil.
See Fig. 7 . Install upper seal into block with lip facing toward front
of engine.
2) Apply Silicone sealer on both sides of lower seal tabs.
Ensure no sealer is applied on seal lip. Apply liquid soap on seal-to-
cap contact surfaces.
3) Install lower seal into bearing cap with lip facing toward
front of engine. Ensure seal is firmly seated in bearing cap. Apply
Silicone sealer to chamfered edges of bearing cap. See Fig. 7.
CAUTION: DO NOT apply Silicone sealer on cap-to-block contact
surfaces. Sealer should only be applied to chamfered edges
only.
4) Install rear main bearing cap. Tighten main bearing cap
bolts to specification.
Fig. 7: Installing Rear Main Bearing Oil Seal
Courtesy of Chrysler Motors.
WATER PUMP

proper increased enrichment for the next engine start. Idle speed is
nonadjustable.
EMISSION CONTROL
The ECU electrically controls Exhaust Gas Recirculation (EGR).\
An ECU-controlled solenoid valve is used to control EGR valve
function. This valve is located on the left inner fender panel and is
operated by the ECU in response to coolant temperature, throttle
position, and manifold pressure.
Under conditions of engine warm-up, engine idle, wide open
throttle, or rapid acceleration/deceleration, the solenoid valve is
energized, blocking vacuum to the EGR valve. At normal operating
temperatures with engine speed above idle, the solenoid valve is de-
energized, allowing normal EGR valve function.
NOTE: If the electrical connector is removed from the EGR solenoid,
EGR flow will be allowed at all times.
A/C CLUTCH CONTROL
The ECU controls the A/C compressor clutch to improve idle
quality. The A/C compressor clutch will be engaged or disengaged as
deemed necessary by the ECU through the A/C clutch relay.
SHIFT LIGHT CONTROL
The shift light system is used on all manual transmission
equipped vehicles. The ECU monitors coolant temperature, throttle
position, vehicle speed, and engine speed to control the shift light.
The ECU calculates what gear position the vehicle should be in and
uses this information to turn on the light. The light indicates the
best shift point to the driver for maximum fuel economy.
The light is tested when the ignition switch is turned on.
When the engine is started, the light should go out. A transmission-
mounted switch prevents the light from illuminating when the
transmission is shifted into high gear. The ECU turns the light off if
the shift to the next higher gear is not performed within 3-5 seconds
after light comes on.
DIAGNOSIS & TESTING
PRELIMINARY CHECKS
Before assuming that the ECU is faulty, the following systems
and components must be in good condition and operating properly:
* Air filter.
* All support systems and wiring.
* Battery connections and specific gravity.
* Compression pressure.
* Electrical and vacuum connections to components, sensors and
switches.
* Emission control devices.
* Ignition system.
* All vacuum and fuel line (hose) connections.
FUEL SYSTEM TEST
Fuel Pressure
1) Remove cap from pressure test port on fuel rail and

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A/C C O M PR ESSO R O IL C HEC KIN G

1988 J e ep C hero ke e
A/C General Servicing
COMPRESSOR OIL CHECK
* PLEASE READ THIS FIRST *
CAUTION: When discharging air conditioning system, use only approved
refrigerant recovery/recycling equipment. Make every attempt
to avoid discharging refrigerant into the atmosphere.
ISOLATING COMPRESSOR - GRAND WAGONEER ONLY
1) Connect service gauge set to the compressor service valves
and open compressor valves slightly (turn clockwise). Start engine and\
operate air conditioning. Slowly turn compressor suction valve
clockwise toward closed (front-seated) position.
2) When suction pressure is reduced to zero or less, turn off
engine and compressor and quickly turn suction valve stem in to full
front-seated position. Suction pressure should be slightly above zero.
Turn discharge valve into front-seated position.
3) To check oil lever, slowly open crankcase plug to relieve
any remaining pressure. After oil level is correct, cap service gauge
parts on both valves. Back-seat suction service valve to allow
refrigerant to enter compressor. Open discharge valve halfway.
4) Loosen discharge service valve cap, allowing refrigerant
pressure to force air out of compressor. Back-seat service valve and
tighten cap. Compressor is now ready for operation.
REFRIGERANT OIL
Only new, pure, moisture-free refrigerant oil should be used
in the air conditioning system. This oil is highly refined and
dehydrated to a point where moisture content is less than 10 parts per
million. The oil container must be tightly closed at all times when
not in use, or moisture will be absorbed from the air and introduced
into the refrigeration system.
DISCHARGING SYSTEM
CAUTION: When discharging air conditioning system, use only approved
refrigerant recovery/recycling equipment. Make every attempt
to avoid discharging refrigerant into the atmosphere.
If compressor has stem-type service valves, it can be
isolated and removed without discharging entire system. Otherwise,
discharge system completely using approved refrigerant
recovery/recycling equipment before loosening any fittings.
DISCONNECTING LINES & FITTINGS
After system is discharged, carefully clean area around all
fittings to be opened. Always use 2 wrenches when tightening or
loosening fittings to avoid twisting or distorting lines. Cap or plug
all openings as soon as lines are removed. Do not remove caps until
immediately before connections are made. This will keep entry of air
and moisture to a minimum, reducing the chance of damage to
components.

Isolating Compressor
1) Connect manifold gauge set to service valves on
compressor. Close both gauge valves. Open both service valves to the
mid-position.
2) Start engine and operate air conditioning. Turn suction
service valve slowly clockwise toward front-seated position. When
suction pressure is reduced to zero or less, stop engine and quickly
close suction service valve (front-seated).
3) Front-seat the discharge valve. Loosen oil check plug
slowly to release any internal pressure. Service valves can now be
removed from compressor and compressor removed from vehicle (if
necessary). Purge compressor after servicing.
Purging Compressor
1) Remove gauge set and place caps on service valve ports.
Back-seat the suction service valve to allow refrigerant to enter
compressor.
2) Loosen discharge port valve slightly. Loosen valve port
cap to allow refrigerant to force out air from compressor. Back-seat
the discharge valve and tighten the port cap. Compressor is ready for
service.
Compressor Oil Check
1) Operate system for 10 minutes, then stop and isolate
compressor. Loosen filler plug slowly to release any pressure in
crankcase.
2) Use dipstick to check oil level. See Fig. 2. Add oil as
necessary. Install plug with new "O" ring. Purge compressor of air.
Fig. 2: York Compressor Oil Level Dipstick
Check oil with shaft keyway facing head.
SYSTEM SERVICING CAUTIONS

Fig. 3: Assembling Ford Spring-Coupling Fitting
3) Lubricate both sides of fitting with clean refrigeration
oil. Assemble the fitting by pushing together with a slight twisting
motion. Check to make sure spring is over flared end of female
fitting.
PLACING SYSTEM IN OPERATION
After component replacement and/or system servicing has been
completed and all connections have been made, proceed as follows:
1) Evacuate the system using vacuum pump.
2) Charge the system with R-12. See REFRIGERANT CAPACITY in
the A/C SYSTEM SERVICE SPECIFICATIONS in this article.
3) Leak test the system, with particular attention to all new
connections and components.
4) Make a performance test of the system. Never assume that a
recharging has automatically corrected a problem.
DIAGNOSTIC PROCEDURES
Diagnosis is an important first step in A/C system servicing.
To save time and effort, systems should be carefully checked to
identify the causes of poor performance. By using the following
diagnostic charts, defective components or system damage can be
quickly located. To identify problems that are specific to one system,
refer to the repair sections of this article. The charts in this
article apply to all systems.
PREPARATION FOR TESTING
1) Attach Low and High side gauges.
2) Start engine and allow it to warm up.
3) Set system to COOL and blower to HIGH.
4) Open car doors and hood.
5) Run at fast idle for 2-3 minutes.

control module before starting diagnosis or repair procedure, as this
connection is disturbed when Cruise Command System Tester (AM PC-1-R)
is used. Poor connection at this point may be improperly diagnosed as
control module malfunction.
Brake light and clutch switches should be properly adjusted.
Ensure that all vacuum lines are correctly routed and tightly
connected.
CRUISE COMMAND SYSTEM TESTS
Testing is performed with Cruise Command System Tester (AM
PC-1-R). Remove wire harness connector from control module. Connect
tester to wire harness connector. Perform tests as part of service
diagnosis to determine cause and correction of system malfunction.
Various tester lights are associated with specific components,
circuits, etc.
CONTROL SWITCH CONTINUITY
Wrangler
NOTE: Voltage checks should show battery voltage. If resistance
readings are incorrect, check circuit for an open or a
short. Cruise control module terminal No. 1 grounds through
connector at engine block.
Light No. 1 "OFF" (Set Switch)
With control switch in "ON" position, check for battery
voltage between HAZ/STOP and in-line fuse, terminal No. 14 and ground
terminal No. 1
Light No. 2 "OFF" (Control Switch & Speed Sensor)
With control switch in "ON" position, check for battery
voltage between HAZ/STOP and in-line fuse, terminal No. 5 and ground
terminal No. 1. With ignition switch in "OFF" position, check
resistance between terminals No. 2 and No. 3. Resistance should be 15-
50 ohms.
Light No. 3 "OFF" (Brake Light Ground)
With ignition switch in "ON" position, install jumper wire
between terminals No. 7 and No. 13. If brake lights do not turn on,
check fuses and brake light switch connections.
Light No. 4 "OFF" (Throttle Position Feedback Sensor)
With ignition switch in "ON" position, check for battery
voltage between gauge fuses at terminals No. 7 and No. 1.
With ignition switch in "OFF" position, check resistance
between terminals No. 2 and No. 11. Resistance should be 2400-4000
ohms. At idle resistance should be 2800-4300 ohms and at wide open
throttle resistance should be 4000 ohms.
Light No. 5 "OFF" (Resume/Accel/Vent Valve)
With control switch in "RESUME/ACCEL" position, check for
battery voltage between HAZ/STOP and in-line fuse, terminal No. 10 and
ground terminal No. 1. With ignition switch in "OFF" position, check
resistance between terminals No. 6 and No. 12. Resistance should be
30-50 ohms. Resistance between terminals No. 6 and ground, and
terminal No. 12 and ground should be infinite (open).
Light No. 6 "OFF" (Resume/Accel/Charge Valve)
With control switch in "RESUME/ACCEL" position, check for
battery voltage between HAZ/STOP and in-line fuse, terminal No. 10 and
ground terminal No. 1. With ignition switch in "OFF" position, check
resistance between terminals No. 4 and No. 12. Resistance should be

With ignition and control switches in "OFF" position, test
lights should be off. If one or more lights are on, remove Brown (5)
wire at control module connector and check for direct source of
voltage or repair defective control switch.
SYSTEM ELECTRICAL CONTINUITY
Cherokee, Comanche & Wagoneer
1) With ignition and control switches in "ON" position,
lights No. 2, 3 and 4 should be on. Lights No. 1, 5 and 6 should be
off. If light No. 2 is off, check speed sensor continuity, check speed
sensor terminals to Gray and Drk. Blue wires, and check terminals No.
2, 3, 5 and 7 (Gray, Drk. Blue and Lt. Green wires are not grounded).
2) If light No. 3 is off, check brake light switch and all
Brown, Lt. Blue and Lt. Green wire connections. If light No. 4 is off,
check terminals No. 2 and No. 11 at control module connector. Check
continuity of throttle position feedback rheostat of servo.
Grand Wagoneer
1) With ignition and control switches in "ON" position,
lights No. 1, 2, 3, and 4 should be on. Lights No. 5 and 6 should be
off. If light No. 1 is off, check for blown fuse in brake light switch
to control switch circuit. Check Red, Brown and Green wires at control
switch for continuity to switch. Check Drk. Green wire (14) at control\
module connector for continuity to control module.
2) If light No. 2 is off, check speed sensor for correct
output voltage. Check Gray and Drk. Blue wire at speed sensor
connector for continuity to control module connector. Check terminals
No. 2, 3, 5 and 7 at control module connector for proper connection to
wires.
3) If light No. 3 is off, check brake and clutch switch
adjustment. If light No. 4 is off, check for defective connection at
terminals No. 2 and 11 on control module connector. Check operation of
throttle position feedback rheostat on servo.
COAST CONTINUITY TEST
Cherokee, Comanche & Wagoneer
1) With ignition and control switches in "ON" position,
depress and hold "SET/COAST" button. Lights No. 1, 2, 3 and 4 should
be on. Lights No. 5 and 6 should be off. If light No. 1 is off, check
voltage from brake light switch, check 4-amp in-line fuse of Pink
wire, and check Pink, Brown and Drk. Green wires at control switch
connector and Drk. Green (14) wire at control module connector for
good connections.
2) If light No. 2 is off, check speed sensor continuity,
check speed sensor terminals to Gray and Drk. Blue wires, and check
terminals No. 2, 3, 5 and 7 (Gray, Drk. Blue and Lt. Green wires) for
ground.
3) If light No. 3 is off, check brake light switch, check all
Brown, Lt. Blue and Lt. Green wire connections. If light No. 4 is off,
check terminals No. 2 and 11 at control module connector, and check
continuity of throttle position feedback rheostat of servo.
SERVO CHARGE VALVE SOLENOID CONTINUITY
CAUTION: If engine is running, servo will move throttle to wide open
position.
Grand Wagoneer
1) With ignition and control switches in "ON" position,
depress and hold "SET/COAST" button. Lights No. 2, 3, 4, 5 and 6
should be on. Light No. 1 should be off. Light No. 4 will dim when

servo moves throttle to wide open position with engine operating.
2) If light No. 2 is off, check speed sensor for correct
output voltage. Check Gray and Drk. Blue wire at speed sensor
connector for continuity to control module connector. Check terminals
No. 2, 3, 5 and 7 at control module connector for proper connection to
wires.
3) If light No. 3 is off, check brake and clutch switch
adjustment. If light No. 4 is off, check for defective connection at
terminals No. 2 and 11 on control module connector. Check operation of
throttle position feedback rheostat on servo.
4) If light No. 5 is off, check for defective connections at
terminals No. 4 and 12 on control module connector. If necessary,
replace defective servo. If light No. 6 is off, check for defective
connection at terminals No. 6 and 12 on control module connector. If
necessary, replace defective servo.
5) If all lights are off after depressing set/coast speed
switch, check for blown fuse. Check for short circuits in Red, Pink
and Brown wire circuits at control switch. If necessary, replace
defective servo.
SYSTEM DISENGAGEMENT WITH BRAKE PEDAL DEPRESSED
Cherokee, Comanche & Wagoneer
1) With ignition and control switches in "ON" position and
brake pedal depressed, lights No. 2 and 4 should be on. Lights No. 1,
3, 5 and 6 should be off. Light No. 3 should be on when brake pedal is
released.
2) If light No. 2 is off, check speed sensor continuity,
check speed sensor terminals to Gray and Drk. Blue wires, and check
terminals No. 2, 3, 5 and 7 (Gray, Drk. Blue and Lt. Green) for
ground.
3) If light No. 4 is off, check terminals No. 2 and 11 at
control module connector, and check continuity of throttle position
feedback rheostat of servo.
Grand Wagoneer
1) With ignition and control switches in "ON" position and
brake pedal depressed, lights No. 1, 2 and 4 should be on. Lights No.
3, 5 and 6 should be off. Light No. 3 should be on when brake pedal is
released.
2) If light No. 1 is off, check for blown fuse in brake light
switch to control switch circuit. Check Red, Brown and Green wires at
control switch connector for continuity to switch. Check Drk. Green
wire (14) at control module connector for continuity to control
module.
3) If light No. 2 is off, check speed sensor for correct
output voltage. Check Gray and Drk. Blue wire at speed sensor
connector for continuity to control module connector. Check terminals
No. 2, 3, 5 and 7 at control module connector for proper connection to
wires.
4) If light No. 4 is off, check for defective connection at
terminals No. 2 and 11 on control module connector. Check operation of
throttle position feedback rheostat on servo. If light No. 3 is off
when brake pedal is released, check brake light switch adjustment.
"RESUME/ACCEL" FUNCTION
CAUTION: If engine is running, servo will move throttle to wide open
position.
Cherokee, Comanche & Wagoneer
1) With ignition and control switches in "ON" position, slide
and hold control switch in "R/A" position. Lights No. 2, 3, 4, 5 and 6