1988 JEEP CHEROKEE engine

Fig. 23: Chart 4-K - System Operational Test (Cont.)
Fig. 24: Chart 5 - Basic Engine Test

THROTTLE BODY ASSEMBLY
Removal
1) Remove throttle return spring, throttle cable and cruise
control cable, if equipped. Disconnect wiring harness connector from
injector, WOT switch, and ISA motor. Remove fuel supply and return
pipes from throttle body.
2) Identify and tag vacuum hoses for installation later.
Disconnect vacuum hoses from throttle body assembly. Remove throttle
body-to-manifold retaining nuts from studs.
3) Remove throttle body assembly from intake manifold. If
being replaced, transfer ISA motor and WOT switch and bracket
assembly to new throttle body.
Installation
To install, reverse removal procedure using a new gasket
between components. Adjust ISA motor and WOT switch.
FUEL INJECTOR
Removal
Remove air cleaner assembly, injector wire connector, and
injector retainer clip screws. Using a pair of small pliers, gently
grasp center collar of injector (between electrical terminals), and
carefully remove injector with a lifting and twisting motion. Note
back-up ring fits over upper "O" ring.
Installation
1) Lubricate new lower "O" ring with light oil and install
in housing bore. Lubricate new upper "O" ring with light oil and
install in housing bore. Install back-up ring over upper "O" ring.
2) Position new injector in fuel body, and center nozzle in
lower housing bore. Seat injector with a pushing and twisting motion.
Align wire connector terminals properly. Install retainer clip and
screws. Connect injector wire connector.
FUEL PRESSURE REGULATOR
Removal
Remove 3 retaining screws, securing pressure regulator to
fuel body. After noting location of components for reassembly
reference, remove regulator assembly.
Installation
Position pressure regulator assembly with a new gasket.
Install 3 retaining screws, securing regulator to throttle body.
Adjust regulator. Operate engine and inspect for leaks.
IDLE SPEED ACTUATOR, MOTOR & WIDE OPEN THROTTLE SWITCH
NOTE: Closed throttle (idle) switch is integral with ISA and motor
assembly.
Removal
1) Remove air cleaner assembly. Disconnect throttle return
spring, throttle cable and cruise control cable, if equipped.
Disconnect wiring harness connector from ISA motor and WOT switch.
2) Remove ISA motor and WOT switch bracket from throttle
body. Remove motor-to-bracket retaining nuts. See Fig. 23. Do not
remove nuts from motor studs.
CAUTION: Do not attempt to remove ISA motor attaching nuts without

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.

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

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