JEEP CHEROKEE 1988 Service Workshop Manual

nuts. Install motor and WOT switch bracket assembly on throttle body.
2) Connect wiring harness connector to ISA motor and WOT
switch. Connect the throttle return spring, throttle cable and cruise
control cable. Adjust ISA motor and WOT switch. Install air cleaner
assembly.
NOTE: After replacing or reinstalling the original ISA motor, be
sure motor plunger is fully extended before starting the
engine. If plunger is not fully extended, the closed
throttle switch may open prematurely, causing idle speed to
drop to approximately 400 RPM.
3) Start engine with throttle at 1/4 open position. This
prevents ISA plunger from retracting. Stop engine. When ignition is
turned off, the motor plunger will fully extend. After installation
is complete, adjust ISA as required.
ELECTRONIC CONTROL UNIT
Removal & Installation
Locate ECU in passenger compartment, below glove box. Remove
retaining screws and mounting bracket. Remove the ECU, and disconnect
wiring harness connector from ECU. Reverse removal procedure to
install.
OXYGEN SENSOR
Removal
Disconnect the wire connector from sensor, and unscrew
sensor from exhaust pipe adapter. Clean adapter threads.
Installation
1) Apply anti-seize compound to sensor threads. Do not allow
compound to adhere to any other part of sensor. Hand start the sensor
into place and tighten. Check that wire terminal ends are properly
seated in connector. Connect wire.
2) Do not push the rubber boot over sensor body lower than
1/2" (13 mm) above base of sensor. If the sensor wire should break,
sensor must be replaced. These wires cannot be spliced or otherwise
repaired.
MANIFOLD AIR TEMPERATURE & MANIFOLD ABSOLUTE PRESSURE SENSORS
Removal & Installation
Disconnect wiring harness connector from sensor. Disconnect
vacuum hose from MAP sensor. Remove sensor. Clean MAT sensor manifold
threads, and wrap with Teflon tape. To install, reverse removal
procedure.
COOLANT TEMPERATURE SENSOR (CTS)
Removal & Installation
Allow engine to cool and release pressure from cooling
system. Remove wiring harness from sensor. Remove sensor at rear of
intake manifold, and plug hole to prevent excessive coolant loss. To
install, reverse removal procedure and replace lost coolant.
EGR VALVE & CANISTER PURGE SOLENOID
Removal & Installation
Disconnect wiring harness and vacuum hose from solenoid.
Remove solenoid and bracket as an assembly. Replace solenoid as an

assembly. To install, reverse removal procedure.
ADJUSTMENTS
NOTE: The following adjustment procedures should not be necessary
during normal vehicle operation or maintenance. Adjustment
of the listed components should only be required when a
faulty component is replaced with a new one.
IDLE SPEED ACTUATOR (ISA) MOTOR
1) With air cleaner removed, air conditioner off (if
equipped) and engine at normal operating temperature, connect a
tachometer to terminals 1 (+) and 3 (-) of the small diagnostic
connector D1. See Fig. 16. Turn ignition off and observe ISA motor
plunger. The plunger should move to fully extended position.
2) With ISA plunger fully extended, disconnect wire
connector and start engine. Engine speed should be 3300-3700 RPM. If
not, turn hex head screw on end of plunger until correct speed is
obtained.
3) Hold closed throttle switch plunger all the way in while
opening throttle. Release the throttle. Throttle lever should not make
contact with the plunger. If contact is made, inspect throttle
linkage and/or cable for binding or damage. Repair as needed.
4) Reconnect ISA motor wire connector and turn ignition off
for 10 seconds. Motor should move to fully extended position. Start
engine. Engine speed should be 3300-3700 RPM for a short time and
then fall to normal idle. Turn off engine and remove tachometer.
5) When final adjustments have been made, apply thread
sealer to adjustment screw threads to prevent movement. Install air
cleaner.
WIDE OPEN THROTTLE SWITCH
1) Remove the throttle body assembly from the engine, and
loosen 2 WOT switch retaining screws. Hold throttle in wide open
position, and attach a Throttle Angle Gauge (J-26701) to flat surface
of the throttle lever.
2) Rotate scale to align the 15
mark with the pointer.
Level the gauge. Rotate scale to align zero with the pointer, and
close the throttle enough to center bubble. This positions the
throttle at 15
before wide open throttle.
3) Adjust the WOT switch lever on the throttle cam so that
the plunger is just closed at 15
position. Tighten the retaining
screws, and remove the gauge.

Fig. 28: Jeep 2.5L TBI System Wiring Diagram
FUEL PRESSURE REGULATOR
1) Remove air cleaner assembly. Connect a tachometer to
terminals 1 and 3 of small diagnostic connector D1. Remove screw plug
and install special Fuel Pressure Test Fitting (8983 501 572).

2) Connect accurate fuel pressure gauge to fuel pressure
test fitting. Start engine and accelerate to 2000 RPM. Turn torx head
adjustment screw on bottom of fuel regulator to obtain 17.3 psi (1.2
kg/cm(C)) of fuel pressure.
NOTE: Turning screw inward increases pressure; turning screw
outward decreases it.
3) After specification is reached, install a lead seal ball
to cover regulator adjustment screw. Turn ignition switch off, and
disconnect tachometer. Disconnect fuel pressure gauge, remove test
fitting, and install original plug screw. Install air cleaner
assembly.

\003
4.0 L 6 -C YL - V IN [ M ] & 4 .2 L 6 -C YL - V IN [ C ]

1 988 J e ep C hero ke e
1988 ENGINES
Chrysler Motors 4.0L & 4.2L 6-Cylinder
Jeep; Cherokee, Comanche, Wagoneer, Wrangler
ENGINE CODING
ENGINE IDENTIFICATION
NOTE: For engine repair procedures not covered in this article,
see ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION article
in the GENERAL INFORMATION section.
The Vehicle Identification Number (VIN) is located on upper
left side of dash and is visible through windshield. The fourth
character identifies the engine size. The tenth character identifies
the model year.
ENGINE IDENTIFICATION CODES TABLE









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Application VIN Code
4.0L 6-Cylinder MPFI ........................ M
4.2L 6-Cylinder 2-Bbl. ...................... C









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SPECIAL ENGINE MARKS
Some engines are produced at factory with oversize or
undersize components. These engines are identified by a letter code
stamped on a boss between ignition coil and distributor. Letters are
decoded as follows:
* "B" indicates all cylinder bores are .010" (.25 mm)
oversize.
* "C" indicates all camshaft bearing bores are .010" (.25 mm)
oversize.
* "M" indicates all main bearing journals are .010" (.25 mm)
undersize.
* "P" indicates all connecting rod journals are .010" (.25 mm)
undersize.
REMOVAL & INSTALLATION
ENGINE REMOVAL
See ENGINE REMOVAL in this section.
INTAKE & EXHAUST MANIFOLD (4.0L)
WARNING: Fuel system is under pressure. Use care when removing fuel
lines to prevent personal injury.
Removal
1) Disconnect negative battery cable. Remove air inlet from
throttle plate assembly. Disconnect throttle, cruise control and
throttle valve (A/T models) cables (if equipped).
2) Disconnect and mark all vacuum and electrical connectors

from intake manifold. Disconnect fuel lines at fuel rail. Fuel lines
are removed by squeezing the 2 retaining tabs against the fuel line
and pulling the fuel line from the connector. Use caution as these
fuel lines are under pressure.
3) Loosen drive belt tensioner and remove drive belt. Remove
power steering pump and bracket from intake manifold. Remove fuel rail
retaining bolts. Remove fuel rail and injector assembly.
4) Remove intake manifold heat shield. Disconnect EGR tube
fittings. Disconnect exhaust pipe from manifold. Disconnect oxygen
sensor. Remove retaining bolts and remove manifolds.
Installation
1) Install new gasket. Install exhaust and intake manifolds
and loosely install bolts. Install EGR tube between manifolds. Tighten
manifold bolts in proper sequence see Fig. 1. Tighten to
specifications, see TORQUE SPECIFICATIONS TABLE in this article.
2) Tighten EGR tube bolts. Apply anti-seize to oxygen sensor
threads prior to installation. Reverse removal procedures for
remaining components. Tighten bolts to specification.
3) Install new "O" rings on fuel line connectors prior to
installation. Ensure "CLICK" sound is heard when installing fuel
lines. This indicates that fuel lines are properly seated.
Fig. 1: Manifold Tightening Sequence (4.0L)
Courtesy of Chrysler Motors.
INTAKE & EXHAUST MANIFOLD (4.2L)
Removal
1) Remove air cleaner. Disconnect fuel line at carburetor.
Mark and disconnect all vacuum hoses, ventilation hoses and electrical
connectors at intake manifold.
2) Disconnect throttle cable at bellcrank. On A/T models,
disconnect throttle valve rod. On all models, remove PCV hose from
manifold. Drain cooling system. Remove coolant hoses from intake

manifold.
3) Remove EGR tube fittings from manifolds. Remove power
steering pump and A/C compressor and mounting brackets (if equipped).
4) Remove intake manifold bolts. Remove intake manifold. If
exhaust manifold requires removal, disconnect exhaust pipe from
manifold. Remove oxygen sensor (if equipped). Remove exhaust manifold.\
Installation
1) Install new gasket. Install exhaust manifold and loosely
install bolts. Install intake manifold. Tighten bolts to specification
in proper sequence. See Fig. 2.
2) Apply anti-seize to oxygen sensor threads prior to
installation. Reverse removal procedure for remaining components.
Tighten bolts to specification. Fill and purge cooling system. See
COOLING SYSTEM AIR PURGE under WATER PUMP in this article.
Fig. 2: Manifold Tightening Sequence (4.2L)
Courtesy of Chrysler Motors.
CYLINDER HEAD
Removal
1) Disconnect negative battery cable. Drain cooling system.
Disconnect hoses at thermostat housing. Remove intake and exhaust
manifolds. See the following:
* INTAKE & EXHAUST MANIFOLD (4.0L) .
* INTAKE & EXHAUST MANIFOLD (4.2L) .
2) Disconnect and mark all hoses and electrical connections
at cylinder head. Disconnect and mark spark plug wires. Remove spark
plugs. Remove valve cover bolts.
3) Remove the rocker arms and the push rods. Remove cylinder
head bolts. Remove cylinder head. See ROCKER ARMS & BRIDGE.
Inspection
Inspect cylinder head for cracks or damage. Using
straightedge, check cylinder head for warpage in several areas. Repair

or replace cylinder head if warpage exceeds .002" (.05 mm) per each 6"\
(152 mm) or damage exists.
Installation
1) Ensure all gasket surfaces are clean. Clean carbon from
combustion chambers and tops of pistons. Apply sealant to both sides
of new cylinder head gasket. Install new gasket with the word "TOP"
upward. Ensure all holes are aligned.
2) Install cylinder head. Apply sealing compound to threads
of cylinder head bolt No. 11 prior to installation. See Fig. 3.
Install head bolts.
3) Tighten all bolts in sequence (except No. 11) to 110 ft.
lbs. (149 N.m) on 4.0L or 85 ft. lbs. (115 N.m) on 4.2L models.
Tighten No. 11 head bolt to 100 ft. lbs. (136 N.m) on 4.0L or 75 ft.
lbs. (136 N.m) on 4.2L. See Fig. 3.
4) Reverse removal procedure for remaining components.
Install valve cover and new gasket. Tighten bolts to specification.
5) Refill and purge cooling system. See COOLING SYSTEM AIR
PURGE under WATER PUMP in this article.
Fig. 3: Cylinder Head Bolt Tightening Sequence
Courtesy of Chrysler Motors.
Valve Arrangement
E-I-I-E-I-E-E-I-E-I-I-E (Front-to-rear).
ROCKER ARMS & BRIDGE
Removal
1) Remove PCV valve hose at valve cover. Remove cruise
control servo (if equipped). Remove valve cover. Alternately loosen
each rocker arm bolt one turn at a time.
2) Remove rocker arm assemblies and push rods. Mark
components for reassembly. Components must be installed in original
location.
Installation
Reverse removal procedure. Install rocker arm components in
original location. Install valve cover and new gasket. Tighten bolts
to specification.
Valve Guide
Valve guides are not replaceable. If clearance is excessive,
valve guides must be reamed to accommodate oversized stem valves.

VALVE SPRING
Valve springs can be removed without removing cylinder head.
Valve Spring Installed
For 4.0L the Valve Spring Installed Height Specification is
1.625 inches or 41.29 mm. For the 4.2L the information is not
available from manufacturer.
HYDRAULIC VALVE LIFTER
Removal
Remove cylinder head. See CYLINDER HEAD. Using Lifter
Remover/Installer (J-21884), remove lifter. Mark lifter location for
reassembly reference. Replace lifters as an assembly if damaged.
Internal components cannot be interchanged.
Inspection
Inspect lifter and camshaft mating surfaces for wear. Check
cylinder block lifter bore diameter. Lifter bore diameter should be
within .9055-.9065" (22.999-23.025 mm). Replace parts as necessary.
Installation
Soak lifter assembly in engine oil prior to installation.
Reverse removal procedure for installation. Install lifter in original
location.
ENGINE FRONT COVER
Removal
1) Disconnect negative battery cable. Remove drive belts, fan
and hub assembly. Remove pulley from vibration damper. Remove
vibration damper retaining bolt and washer.
2) Using Puller (J-21719-01), remove vibration damper and
key. Remove alternator and A/C compressor bracket (if equipped).
Remove oil pan-to-front cover bolts. Remove cover-to-block retaining
bolts. Remove front cover.
3) Cut oil pan gasket tabs even with face of cylinder block.
Remove tabs. Remove gasket from oil pan. Pry crankshaft oil seal from
cover.
Installation
1) Ensure all gasket surfaces are clean. Ensure oil slinger
is installed on crankshaft. Apply sealing compound on both sides of
front cover gasket. Install gasket on cylinder block. Replace front
section of oil pan seal with similar section fabricated from new seal.
2) Coat seal with RTV sealant and place in position. Apply
sealant to the joint area of oil pan and cylinder block. Apply engine
oil on seal-to-oil pan contact areas.
3) Place front cover on cylinder block. Place Front Cover
Seal Installer (J-22248) in front cover seal area. Install all
retaining bolts. Tighten bolts to specification.
4) Install front cover oil seal. See FRONT COVER OIL SEAL in
this article. Remove front cover seal installer. Reverse removal
procedure for remaining components. Lubricate vibration damper
retaining bolt with oil prior to installation. Tighten bolts to
specification.
FRONT COVER OIL SEAL
1) Remove vibration damper. Pry seal from front cover. Use

care not to damage seal area. Position new seal on Front Cover Seal
Installer (J-22248) with lip facing outward.
2) Apply sealant to seal outer diameter. Lightly coat
crankshaft with oil. Place front cover seal installer on front of
crankshaft. Tap seal into front cover. Lightly coat seal contact area
of vibration damper with oil.
3) Install key in crankshaft (if removed). Install vibration\
damper. Lubricate vibration damper bolt with oil. Install retaining
bolt and washer. Tighten to specification.
TIMING CHAIN & SPROCKET
Removal
1) Drain cooling system. Remove radiator. Remove engine front
cover. See ENGINE FRONT COVER in this article. Remove oil slinger.
Rotate crankshaft until timing marks on sprockets are aligned. See
Fig. 4 .
2) Remove camshaft sprocket bolt. Remove timing chain and
both sprockets as an assembly.
Installation
Install timing chain and sprockets. Ensure timing marks are
aligned. See Fig. 4. Install camshaft sprocket bolt. Tighten bolts to
specification. Install new front cover oil seal. Reverse removal
procedure for remaining components.
Fig. 4: Timing Chain & Sprocket Alignment
Courtesy of Chrysler Motors.
CAMSHAFT