engine JEEP CHEROKEE 1988 Service Repair Manual

Fig. 1: 2.5L Firing Order & Distributor Rotation
IGNITION TIMING
NOTE: No adjustment is possible on models with Renix ignition.
HOT (SLOW) IDLE RPM
NOTE: Adjust ISC motor plunger only after replacing ISC motor.
Idle Speed Control (ISC) Motor Plunger
1) Remove air cleaner, turn off A/C (if equipped) and warm
engine to normal operating temperature. Connect tachometer negative
lead to diagnostic connector terminal "D1-3" and positive lead to
connector terminal "D1-1". See Fig. 2. Turn ignition off. ISC plunger
should fully extend.

Fig. 2: TBI Diagnostic Connector & Terminal ID
Courtesy of Chrysler Motors.
2) With plunger extended, disconnect ISC motor electrical
connector. Start engine. Engine idle speed should be 3300-3700 RPM. If
not, turn plunger hex head to obtain 3500 RPM. See Fig. 3.
3) To fully retract ISC motor, hold closed throttle switch
plunger inward while opening throttle. Closed throttle switch plunger
should not touch throttle lever when throttle is closed. If this
occurs, check linkage and/or cable for binding.

Fig. 3: TBI Idle Speed Control (ISC) Motor Adjustment
Courtesy of Chrysler Motors.
4) Connect ISC motor connector. Turn ignition off for 10
seconds. ISC motor should fully extend. Restart engine. Engine speed
should momentarily be about 3500 RPM and return to idle speed. Turn
ignition off and disconnect tachometer. Apply sealant to adjustment
screw threads. Install air cleaner.
IDLE SPEED (RPM)









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Application Curb Idle
2.5L TBI (ISC Plunger Extended) ............................... 3500\









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NOTE: Holding plunger inward may create an intermittent trouble
code in ECU memory. To clear ECU memory, turn ignition off
and disconnect negative battery cable for 10 seconds.
THROTTLE POSITION SENSOR (TPS) ADJUSTMENT
NOTE: On some models, it may be necessary to remove throttle body
from intake manifold, to access sensor wiring harness.
Automatic Transmission
1) Locate the square TPS connector. Note connector terminal
identification stamped on the back of the connector. Turn ignition on.
2) Connect voltmeter through back of wiring harness

NOTE: Idle mixture adjustment is not possible on TBI models.
COLD (FAST) IDLE RPM
NOTE: Fast idle is not adjustable on TBI models.
SERVICING
EMISSION CONTROL
See EMISSIONS section.
SPECIFICATIONS
IGNITION
Distributor
All models are equipped with Renix solid state ignition.
IGNITION COIL RESISTANCE - OHMS @ 75
F (24C)








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Application Primary Secondary
2.5L ........................ .4-.8 .................... 2500-4000









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FUEL SYSTEM
FUEL INJECTION








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Application Model
2.5L ..................................................... Renix TBI









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Fuel Pump
The 2.5L engine with TBI uses an electric fuel pump located
in the tank.
FUEL PUMP SPECIFICATIONS









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Application Pressure: psi (kg/cm) Volume: Pts. (L)
2.5L (TBI) .............. 14.5 (1.0) ......................... N\
/A









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BATTERY
BATTERY SPECIFICATIONS








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Application Cold Cranking Reserve Capacity
** ( 1) Amps Minutes
Standard ..................... 421 ............................ 75
Optional ..................... 452 ............................ 81
( 1) - At 0
F (-18C).








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STARTER

All 2.5L engines use a Bosch positive engagement starter.
STARTER SPECIFICATIONS









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Application Volts Amps Test RPM
2.5L .................. 12 ............ 75 ................ 2900









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ALTERNATOR
All 2.5L engines use a Delco-Remy 10SI or 12SI alternator
with integral regulator.
ALTERNATOR SPECIFICATIONS









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Application Field Current Rated Amp
** Draw @ 12 Volts Output
Standard ................ 4.0-5.0 Amps ........................ 56
Optional ................ 4.0-5.0 Amps ........................ 66
Optional ................ 4.0-5.0 Amps ........................ 78









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ALTERNATOR REGULATOR
All 2.5L models use Delco-Remy nonadjustable regulators,
integral with alternator.
REGULATOR OPERATING VOLTAGE @ 80
F (27C)








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Application Voltage
2.5L ..................................................... 13.9-14.9









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BELT ADJUSTMENT
BELT ADJUSTMENT - TENSION IN LBS. (KG) USING STRAND TENSION GAUGE








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Application New Belt Used Belt
"V" Belts ( 1) .......... 125-155 (57-70) .......... 90-115 (41-52)
Serpentine ............. 180-200 (82-91) ......... 140-150 (64-68\
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( 1) - Adjust new P/S belt to 120-140 lbs. (54-64 kg).









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SERVICE INTERVALS
REPLACEMENT INTERVALS








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Component Interval (Miles)\
Air Filter .................................................. 30,000
Fuel Filter ................................................. 30,000
Engine Oil & Filter ........................................... 7500
PCV Valve ................................................... 30,000
Spark Plugs ................................................. 30,000









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\003
TU NE-U P - 6 -C YL

1988 J e ep C hero ke e
1987-88 TUNE-UP
Jeep 6 Cylinder Tune-Up
Cherokee, Comanche, Wagoneer, Wrangler
IDENTIFICATION
ENGINE IDENTIFICATION
Engine can be identified by the fourth character of engine
Build Date Code number, located on a tag attached to right side of
block between No. 2 and 3 cylinders.
The same code letter is also the fourth character in the
Vehicle Identification Number (VIN), located at top left corner of
dashboard.
ENGINE CODE TABLE









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Engine Code
4.0L (242") MPFI ....................................... M
4.2L (258") 2-Bbl. ..................................... C









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TUNE-UP NOTES
NOTE: When performing tune-up procedures described in this
article, these notes and precautions must be followed.
Due to late changes and corrections, always refer to Emission
Control Label in engine compartment before attempting tune-up. If
manual and label specifications differ, use label specifications.
When performing tune-up on vehicles equipped with a catalytic
converter, do not allow or create an engine misfire in one or more
cylinders for an extended period of time. Damage to converter from
overheating may occur due to loading with unburned fuel.
TESTING
ENGINE COMPRESSION
Check compression pressure with engine at normal operating
temperature, all spark plugs removed, throttle and choke valves wide
open and engine at cranking speed.
COMPRESSION SPECIFICATIONS TABLE









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Application Specification
Compression Ratio .................................. 9.2:1
Compression Pressure ....... 120-150 psi (8.4-10.5 kg/cm
)
Maximum Variation Between Cylinders .. 30 psi (2.1 kg/cm)








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HIGH TENSION WIRE RESISTANCE
Do not puncture spark plug wires with any type of probe.
Remove spark plug wire and check resistance using an ohmmeter.

inlet line or filter disconnected at carburetor. Disconnect fuel
return line at fuel filter and plug nipple on filter. Make all tests
at idle speed. See FUEL PUMP SPECIFICATIONS TABLE .
FUEL PUMP SPECIFICATIONS TABLE









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Application Pressure Volume
** psi (kg/cm) ( 1) Pts. (L)
4.0L .................... ( 2) 31 (2.1) ............ 1.0 (.47)
4.0L .................... ( 3) 39 (2.6) ............ 1.0 (.47)
4.2L .................. 4.0-5.0 (.28-.35) ......... 1.0 (.47)
( 1) - Volume per 30 seconds.
( 2) - With the vacuum hose connected to the pressure regulator.
( 3) - With the vacuum hose removed from the pressure regulator.









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ADJUSTMENTS
VALVE ARRANGEMENT
* E-I-I-E-I-E-E-I-E-I-I-E (Front-to-rear).
VALVE CLEARANCE
All engines are equipped with hydraulic lifters. Valve
clearance is not adjustable.
IGNITION COIL WIRE
Remove ignition coil wire from coil and distributor cap.
Check terminals for corrosion and clean (if necessary). Check coil
wire resistance. Replace wire if resistance is excessive.
HIGH TENSION WIRE RESISTANCE (OHMS) TABLE









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Wire Length Minimum Maximum
0-15" .................. 3000 ................... 10,000
15-25" ................. 4000 ................... 15,000
25-35" ................. 6000 ................... 20,000
Over 35" ............... 8000 ................... 25,000









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DISTRIBUTOR
4.0L
Information not available from manufacturer.
4.2L
All models are equipped with Motorcraft Solid State Ignition
(SSI) systems. No adjustments are required.

Fig. 2: 4.0L & 4.2L Timing Marks & Firing Order
Magnetic probe located at 9.5 degrees ATDC on 4.2L.
IGNITION TIMING (4.0L)
Information not available from manufacturer.
IGNITION TIMING (4.2L)
NOTE: Engines are equipped with a receptacle for a magnetic probe
timing light, located 9.5 degrees ATDC. Do not use this
location to check timing with a conventional light, use a
magnetic probe timing light.
Standard Timing Procedure
1) Apply parking brake, and place transmission in Neutral
(Park for automatic transmissions). Operate engine to normal operating\
temperature. Turn ignition off. Install timing light.
2) Connect tachometer. Disconnect and plug vacuum hose at
distributor. Disconnect vacuum switch assembly wire connector, located
on top of valve cover. Start engine and increase engine speed to 1600
RPM.
3) Compare timing to specification. See
IGNITION TIMING SPECIFICATIONS table. To adjust timing, loosen
distributor clamp bolt and turn distributor. Recheck timing after
clamp bolt is tightened.
Alternate Timing Procedure
1) Apply parking brake and place transmission in Neutral
(Drive for automatic transmissions). Operate engine to obtain normal
operating temperature. Turn ignition off. Install timing light.
2) Disconnect and plug vacuum switch hose (Red and Black

wires connected to switch). Disconnect distributor vacuum advance hose
and connect hose to vacuum switch. Disconnect wire connector from
knock sensor, located in cylinder head.
3) Using a jumper wire, ground knock sensor wire connector to
engine block. Start engine. With engine at idle speed (solenoid
energized), check timing. Adjust timing to one degree more than
specification (if required). See Emission Control Label.
IGNITION TIMING SPECIFICATIONS (DEGREES BTDC@RPM) - 4.2L









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Application Man. Trans. Auto. Trans.
50 State ............. 9 @ 1600 ............... 9 @ 1600
High Altitude ........ 16 @ 1600 ............. 16 @ 1600









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HOT (SLOW) IDLE RPM
4.0L
1) Apply parking brake and place transmission in Neutral
(Drive for automatic transmissions). Operate engine to normal
operating temperature. Turn ignition off.
2) Ensure all accessories are off. Connect positive
tachometer lead to terminal "D1-1" and negative lead to "D2-7" of
diagnostic connectors. See Fig. 3. Disconnect air stepper motor
connector and TPS wiring connector. See Fig. 4.
Fig. 3: Diagnostic Connector Terminal Identification
Courtesy of Chrysler Motors.

Fig. 4: Installing Air Stepper Motor Exerciser
Courtesy of Chrysler Motors.
3) Install Air Stepper Motor Exerciser (Ele.CT01) on the air\
stepper motor connector. See Fig. 4. Install the Red terminal of the
air stepper exerciser on the positive battery post and the Black
terminal on the negative battery terminal.
4) Start engine and place stepper motor exerciser switch on
the "LOW" position and note engine RPM. Idle speed should be 750F50
RPM. Disconnect and remove air stepper motor exerciser.
5) If adjustment is required, turn ignition off. Remove the
welch plug from the RPM adjusting screw cavity. See Fig. 5. Turn RPM
adjusting screw inward 2 turns. Start the engine and note engine RPM.