check engine JEEP CHEROKEE 1988 Service User Guide

engine.
3) Install bearings. Check oil clearance and connecting rod
side play clearance. Reverse removal procedure for remaining
components. Tighten bolts to specification.
Fitting Pistons
1) Determine cylinder taper, wear and out-of-roundness and
piston clearance. For cylinder specifications, see CYLINDER, PISTON &
ROD SPECIFICATIONS table. If taper or out-of-roundness are not within
specification, hone or bore cylinders for installation of new pistons.
2) Measure piston at right angle of the piston pin at the
center line of the pin. Compare reading to cylinder bore to determine
clearance. Mark fitted piston for cylinder location.
CYLINDER, PISTON & ROD SPECIFICATIONS TABLE









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Application In. (mm)
Connecting Rod
Crankshaft Bore ................ 2.2080-2.2085 (56.083-56.095)
Pin Bore ......................... .9288-.9298 (23.591-23.616)
Cylinder Bore
Diameter
4.0L ......................... 3.8751-3.8775 (98.427-98.488)
4.2L ......................... 3.7501-3.7533 (95.252-95.334)
Out-of-Round ...................................... .001 (.02)
Taper ............................................. .001 (.02)
Piston Pin Bore Diameter ........... .9308-.9313 (23.642-23.655)
Piston Pin Diameter ................ .9304-.9309 (23.632-23.644)
Piston-to-Cylinder Clearance ..... .0009-.0017 (.022-.043)









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PISTON PIN
NOTE: Note direction of arrows on piston and oil squirt hole in
connecting rod location prior to removal.
Removal
Position piston on Support (J-21872-1), Pin Pilot (J-21872-2\
)
and Driver (J-21872-3) on an arbor press. See Fig. 6. Note location of
piston pin through gauge window. Press piston pin from piston.
NOTE: Piston and pin must be at standard room temperature when
measuring fit. Piston pin should gravity-fall through the
piston at room temperature. Piston pin cannot be reused
after removal.
Inspection
Measure piston pin diameter, piston bore and connecting rod
bores. Replace components if not within specification. See CYLINDER,
PISTON & ROD SPECIFICATIONS table.
NOTE: Rod must be positioned on the piston so the oil squirt hole
faces the camshaft side of the engine when piston is
installed with arrow toward the front of the engine.
Installation
1) Insert pin pilot through piston and connecting rod. Place
assembly on support. Insert piston pin through the upper piston pin
bore and into connecting rod pin bore. See Fig. 6.

ROD BEARING
NOTE: Crankshaft journal diameters are indicated by a color coded
mark placed on the adjacent counterweight or cheek toward
the flanged (rear) end of crankshaft. Note color code to
determine proper bearing usage. Check oil clearance after
bearing installation.
Removal
Remove oil pan. See OIL PAN REMOVAL at end of ENGINE section.
Rotate crankshaft to position rod to be serviced at bottom of stroke.
Mark bearing cap and connecting rod. Remove bearing cap with bearing.
Push piston and rod assembly up to remove upper bearing.
Installation
1) Note color code on edge of bearings removed. Install
bearings. Using Plastigage method, check bearing clearances. Replace
bearings as necessary to obtain correct clearance. Bearings are
available in standard and undersize application.
2) If required, different sized upper and lower bearings may
be installed to obtain correct oil clearance. Tighten bolts to
specification. Check rod side play. Rotate crankshaft to ensure
freedom of movement. Reverse removal procedure for remaining
components. Tighten bolts to specification.
NOTE: Avoid combining bearing inserts in excess of .001" (.02 mm)
difference in size.
MAIN BEARING
Removal
Remove oil pan. See OIL PAN REMOVAL at end of ENGINE section.
Ensure main bearing caps are marked for location. Remove bearing cap.
Rotate crankshaft to remove bearings. Note color code on edge of
bearing.
NOTE: Crankshaft main bearing journal diameters are indicated by a
color code. Color code is placed on the adjacent cheek
toward the flanged (rear) end of crankshaft for all except
the rear main. Rear main is color coded on the rear flange.
Note color code to determine proper bearing usage. Check oil
clearance after bearing installation.
Installation
1) Note color code on edge of bearings removed. Install
bearings. Ensure caps are installed in original location with arrow on
cap facing toward front of engine. Using Plastigage method, check
bearing clearances.
2) Replace bearings as necessary to obtain correct clearance.
Bearings are available in standard and undersize applications. If
required, different sized upper and lower bearings may be installed to
obtain correct oil clearance.
NOTE: If different sized bearings are used, odd sized bearings must
all be uniform in location (upper or lower). DO NOT use
bearings with a thickness difference exceeding
.001" (.02 mm).
3) Tighten bolts to specification. Check crankshaft end play.
See CRANKSHAFT END PLAY in this article. Rotate crankshaft to ensure
freedom of movement. Reverse removal procedure for remaining
components. Tighten bolts to specification.

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

COMPONENT TESTING
Throttle Position Sensor
See THROTTLE POSITION SENSOR DIAGNOSTICS chart near the end
of this article. See Fig. 8.
Coolant Temperature Sensor (CTS) &
Manifold Air Temperature (MAT) Sensor
1) Disconnect the electrical connector from the sensor. Using
a high impedance, digital volt/ohmmeter, measure the resistance of the
sensor. If measured resistance is not as specified, replace sensor.
See the CTS & MAT SENSOR TEMPERATURE-TO-RESISTANCE VALUE table.
2) Test electrical harness resistance of both sensors by
testing between ECU harness connector "D-3" and sensor connector. Also
test between sensor connector and ECU harness connector "C-10" ("C-8"
on MAT sensor). Repair wire if open circuit is detected. Repair MAT
sensor wiring harness if resistance is greater than one ohm.
CTS & MAT SENSOR TEMPERATURE-TO-RESISTANCE VALUE









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F(C) Ohms
212 (100) .................................. 185
160 (71) ................................... 450
100 (38) .................................. 1600
70 (21) ................................... 3400
40 (4) .................................... 7500
20 (-7) ................................. 13,500
0 (-18) ................................. 25,000
-40 (-40) .............................. 100,700









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Manifold Absolute Pressure (MAP) Sensor
NOTE: Terminal identification letters are stamped on MAP sensor
body.
1) Disconnect electrical connector from sensor. With ignition
on and engine stopped, measure voltage output of sensor terminal "B".
See Fig. 4 . Ensure wiring harness is okay by also measuring voltage at
ECU terminal "C-t". Output voltage should be 4-6 volts at both points.
Repair or replace wiring harness as required.
2) With ignition on and engine stopped, measure supply
voltage of sensor terminal "C". See Fig. 4. Ensure wiring harness is
okay by also measuring voltage at ECU terminal "C-14". Supply voltage
should be 4.4-5.5 volts at both points. Repair or replace wiring
harness as required.
3) Using an ohmmeter, measure ground circuit resistance at
sensor terminal "A" and ECU connector terminal "D-3". Ensure wiring
harness is okay by also measuring resistance between ECU terminal "D-
3" and "B-11". If ohmmeter indicates an open circuit, check for
defective sensor ground connection at right side of cylinder block.
4) If ground connection is okay, replace ECU. If ECU terminal
"D-3" has short to 12-volts, repair wire before replacing ECU. Repair
or replace wiring harness as required.

Fig. 5: Testing Oxygen Sensor Heating
Element Resistance
Knock Sensor
Knock sensor must be tested with System Tester (M.S. 1700).
Speed Sensor
Disconnect speed sensor electrical connector from the sensor.
Using an ohmmeter, measure resistance between connector terminals "A"
and "B" (marked on connector). If reading is not 125-275 ohms with
engine at normal operating temperature, replace speed sensor.
"Synch Pulse" (Stator)
1) Using an analog voltmeter, insert positive probe into Blue
wire at distributor connector. Insert negative probe into Gray wire
with tracer at distributor connector.
NOTE: Do not remove connector from distributor. Insert voltmeter
leads from rear of connector. Do not puncture wire.
2) With voltmeter set on "15-Volt A/C" scale, turn ignition
on. Voltmeter should indicate 5 volts. If voltage is indicated, go to
step 4). If no voltage is indicated, check voltmeter leads for good
connection and go to next step.
3) If there is still no voltage reading, turn ignition off
and remove ECU. Reconnect harness and turn ignition off and remove
ECU. Reconnect harness and turn ignition on. Check for voltage between
ECU pin "C-16" and good ground. If voltage still does not register,
test system with System Tester (M.S. 1700).
4) If 5 volts was detected, check for continuity at the
following points:
* Between Blue wire at distributor connector and terminal "C-16"
at ECU.
* Between Gray wire with tracer at distributor connector and
terminal "C-5" at ECU.
* Between Black wire at distributor connector and good ground.

If no continuity is shown, repair wiring harness. If
continuity is shown, reconnect voltmeter as in step 2).
5) While observing voltmeter, crank engine. Voltmeter needle
should fluctuate back and forth during engine cranking. This verifies
proper operation of distributor stator. If voltmeter needle does not
fluctuate, replace stator.
EGR Solenoid Valve
1) Make sure vacuum is present at port "C" of the solenoid.
See Fig. 6 . Remove vacuum connector from ports "A" and "B" of
solenoid. Connect vacuum gauge to port "B". Start engine and run at
idle. Vacuum should not be present at port "B".
2) Disconnect electrical connector from solenoid. Vacuum
should now be present at port "B". Stop engine. Reconnect electrical
connector at solenoid. Remove vacuum gauge and reconnect vacuum hoses.
Relays - General Testing
1) The relays used on the 4.0L engine are all of the same
basic construction and design. Terminal No. 30 is usually connected to
battery voltage ("switched" or battery positive at all times).
Terminal No. 87A is connected to terminal No. 30 in de-energized
position.
2) Terminal No. 87 is connected to terminal No. 30 in the
energized position. This connection supplies battery voltage to the
operated device.
3) Terminal No. 86 is connected to the electromagnet of the
operated device; usually through a "switched" power source. Terminal
No. 85 is connected to the electromagnet of the operated device;
usually grounded through a switch or the ECU.
NOTE: Not all relays have battery voltage applied at terminal No.
30. Some may have battery voltage applied at terminal Nos. 87
or 87A. Check design of relay before testing.
4) When testing relays, there should be continuity between
terminal Nos. 87A and 30 when relay is in de-energized position.
Resistance between terminal Nos. 85 and 86 should be 70-80 ohms for
resistor-type relays and 81-91 ohms for diode-type relays.
Fig. 6: Testing EGR Solenoid Valve
Starter Motor Relay
1) Disconnect electrical connectors from terminals "I" and
"G". Using an ohmmeter, measure resistance between the terminals.

ELECTRONIC CONTROL UNIT (ECU)
Removal & Installation
Information not available from manufacturer.
COOLANT TEMPERATURE SENSOR (CTS)
Removal & Installation
Drain cooling system. Remove air cleaner assembly. Disconnect
electrical connector and remove sensor from block. To install, reverse
removal procedure. Refill cooling system.
OXYGEN (O2) SENSOR
Removal & Installation
Raise and support vehicle. Disconnect electrical connector
from sensor. Remove sensor from exhaust manifold. Install and tighten
sensor to 35 ft. lbs. (47 N.m). Reconnect electrical connector. Lower
vehicle.
THROTTLE POSITION SENSOR (TPS)
Removal
Disconnect electrical connector from TPS. Bend lock tabs away
from retaining screws and remove screws. Remove TPS.
Installation
With throttle valve in normal closed position, install TPS.
Install TPS retaining screws. Perform OUTPUT CHECK.
NOTE: Throttle position sensor is nonadjustable. Only output
voltage can be monitored.
Output Check (Manual Transmission Only)
1) Connect negative lead of digital voltmeter to terminal "B"
and positive lead to terminal "A" of TPS connector. Do not disconnect
electrical connector. Insert leads through back of connector. It may
be necessary to remove throttle body from vehicle to gain access to
connector.
2) Turn ignition on, engine off. With throttle closed and
resting against idle stop, input voltage should be about 5 volts. Move
positive lead from terminal "B" to terminal "C" and read voltage
output. Output voltage should be about 0.8 volt with throttle closed
and resting against idle stop.
3) If voltage is not as specified, loosen lower retaining
screw and pivot sensor for large adjustments. Loosen upper retaining
screw and pivot sensor for small adjustments. Adjust sensor so output
voltage reading equals 16 percent of input voltage. If voltage
specifications cannot be obtained, replace sensor. Remove voltmeter.
Tighten screws and bend retaining tabs into position.
ALL OTHER SENSORS, SOLENOIDS & SWITCHES
Removal & Installation
Removal of sensors, switches, and solenoids is accomplished
by disconnecting the electrical and/or vacuum connectors and removing
or detaching the component. To install, reverse removal procedure.
TESTING
NOTE: Refer to Figs. 8-10 for Testing information.

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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.

of the scale, a symbol for defroster indicates defrost position. In
"BI-LEVEL" position, a mixture of floor heat and defroster air is
obtained.
The lower temperature control lever operates blend-air door
in heater core housing. At full right position, all air is directed
through heater core, providing maximum heat flow. At full left
position, all air is directed around heater core providing fresh air.
Control can be set in any intermediate position to provide a blend of
heated and unheated air. Heater must be in heat or defrost mode before
any air can enter vehicle.
TROUBLE SHOOTING
See JEEP TROUBLE SHOOTING at the end of this article.
REMOVAL & INSTALLATION
CONDENSER
Removal (Cherokee, Comanche & Wagoneer) NOTE: On these
models, condenser and receiver-drier are replaced
as a unit.
1) Drain radiator. Disconnect fan shroud and radiator hoses.
Disconnect automatic transmission cooler lines (if equipped).
Discharge A/C system using approved refrigerant recovery/recycling
equipment.
2) Disconnect A/C hoses from condenser. Unplug low pressure
switch. Remove radiator and condenser as an assembly. Detach condenser
retaining bolts. Separate condenser from radiator. Remove receiver-
drier from condenser.
NOTE: Plug receiver-drier openings whenever unit is removed from
condenser. Add 1 oz. of refrigerant oil (AMC No. 8132400) to
system when replacing condenser.
Installation
To install, reverse removal procedure. Fill radiator.
Evacuate, leak test, recharge and check A/C system operation.
Removal (Wrangler)
1) Discharge system (slowly to prevent loss of compressor
oil) using approved refrigerant recovery/recycling equipment. Drain
coolant. Remove fan shroud and radiator. Disconnect pressure line at
condenser. Remove condenser mounting screws. Tilt bottom of condenser
toward engine.
2) From underside of vehicle, disconnect hose attaching
receiver-drier to evaporator. Plug all openings to prevent entry of
dirt or moisture. Remove receiver-drier and condenser assembly. Remove
receiver-drier from condenser.
Installation
To install, reverse removal procedure. Fill radiator.
Evacuate, leak test, recharge and check A/C system operation.
RECEIVER-DRIER
NOTE: On Cherokee, Comanche and Wagoneer, receiver-drier is
removed with condenser and radiator as an assembly.
Removal (Wrangler)