1988 JEEP CHEROKEE Service Repair Manual

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

connector. Connect negative voltmeter lead to terminal "D" and
positive voltmeter lead to terminal "A" to check input voltage. DO NOT
disconnect TPS connector.
3) Hold throttle plate closed against idle stop and note
voltage. Input voltage should be approximately 5 volts. Disconnect
voltmeter positive lead and connect to terminal "B" to measure output
voltage.
4) With throttle plate closed, measure the output voltage.
The output voltage should be approximately .2 volts. If output voltage
is not within specification, loosen TPS retaining screws.
5) Partially tighten one retaining screw. Rotate TPS to
obtain correct output voltage. Tighten retaining screws once correct
voltage is obtained.
Manual Transmission
1) Turn ignition on. Connect voltmeter through back of wiring
harness connector. Connect negative voltmeter lead to terminal "B" and
positive voltmeter lead to terminal "C". DO NOT disconnect TPS
connector. See Fig. 4.
2) Rotate and hold throttle plate in wide open position.
Ensure throttle linkage contacts stop. Note voltmeter reading. Voltage
reading should be 5 volts at wide open throttle. Return throttle plate
to closed throttle position. Disconnect voltmeter positive lead from
sensor terminal "C" and connect it to terminal "A".
3) Rotate and hold throttle plate in wide open position.
Ensure throttle linkage contacts stop. Note voltmeter reading. Output
voltage should be 4.6-4.7 volts. If voltage is not as specified,
loosen sensor mounting screw. Loosen upper sensor mounting screw for
small adjustments and lower screw for large adjustments.
4) Adjust sensor. Tighten sensor mounting screws. Remove
voltmeter and return throttle plate to closed position. Replace sensor
if specified output voltage cannot be obtained.
Fig. 4: Adjusting Throttle Position Sensor (Man Trans)
Courtesy of Chrysler Motors.
IDLE MIXTURE ADJUSTMENT

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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CAPACITIES
FLUID CAPACITIES








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Application Quantity
Auto. Trans. (Dexron II)
Wrangler ......................................... 8.0 qts. (7.6L)\
All Others ....................................... 8.5 qts. (8.0L)\
Cooling System
Wrangler ......................................... 9.0 qts. (8.5L)\
All Others ...................................... 10.0 qts. (9.5L)\
Crankcase (Includes Filter) ........................ 4.0 qts. (3.8L\
)
Drive Axle
Front ............................................ 2.5 pts. (1.2L)\
Rear
Commanche
Standard Capacity ............................ 2.5 pts. (1.2L)\
Metric Ton Axle .............................. 4.8 pts. (2.3L)\
All Others ..................................... 2.5 pts. (1.2L)\
Fuel Tank
Cherokee & Wagoneer
Standard ...................................... 13.5 gals. (51L)\
Optional ........................................ 20 gals. (76L)\
Comanche
Standard ........................................ 16 gals. (60L)\
Optional ...................................... 23.5 gals. (89L)\
Wrangler
Standard ........................................ 15 gals. (57L)\
Optional ........................................ 20 gals. (75L)\
Manual Transmission
AX4 .............................................. 7.8 pts. (3.7L)\
AX5 .............................................. 7.4 pts. (3.5L)\
BA 10/5 .......................................... 3.5 pts. (1.6L)\
Transfer Case (Dexron II)
Wrangler ........................................ 3.25 pts. (1.5L)\
All Others
Command Trac ................................... 2.2 pts. (1.0L)\
Select Trac .................................... 3.0 pts. (1.4L)\









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SYSTEM REFRIGERANT CAPACITIES








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Application Ozs.
All Models ...................................................... 36









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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.

SPARK PLUGS
SPARK PLUG TYPE TABLE








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Application Champion No.
All Models ....................................... RFN14LY









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SPARK PLUG SPECIFICATIONS TABLE








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Gap: In. (mm) Torque: Ft. Lbs. (N.m)
0.035 (0.89) ................................ 7-15 (10-20)









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FUEL PUMP
4.0L
1) Remove the cap from the pressure test port located in the
fuel rail. See Fig. 1. Connect Fuel Pressure Gauge (J-34730-1) to the
pressure fitting.
2) Start vehicle. Pressure should be approximately 31 psi (2.\
1 kg/cm
) with the vacuum hose connected to the pressure regulator and
39 psi (2.6 kg/cm) with the vacuum hose removed from the pressure
regulator. See FUEL PUMP SPECIFICATIONS TABLE .
3) Check the fuel pump flow rate. A good fuel pump will
deliver at least one liter of fuel per minute with the fuel return
line pinched off. If the fuel pump does not pump adequately, inspect
the fuel system for a plugged fuel filter or filter sock.
4) Fuel pump flow rate can be checked by connecting one end
of an old A/C gauge hose to the fuel test port on the fuel rail and
inserting the other end of the hose into a container of at least one
liter or more capacity.
5) Run the fuel pump by installing a jumper wire into
diagnostic connector terminals D1-5 and D1-6. Be sure to pinch off the
fuel return line or most of the fuel will be returned to the fuel
tank.
Fig. 1: Fuel System Pressure Test Components
Courtesy of American Motors/Jeep Corp.
4.2L
Perform fuel pump test with air cleaner removed and fuel

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.