1988 JEEP CHEROKEE cruise control

The ECU controls the A/C compressor clutch by means of the
A/C clutch relay. See Fig. 15.
UP-SHIFT INDICATOR LAMP
Manual transaxle vehicles are equipped with an up-shift
indicator lamp. The lamp is normally turned on when the ignition
switch is turned "ON", and is turned off when the engine starts.
The lamp will again light during engine operation, according
to engine speed and load conditions. A switch, located on the
transaxle, prevents lamp from lighting when transmission is shifted
to the next highest gear. If the shift of gears is not performed, the
ECU will turn the lamp off after 3-5 seconds.
MODES OF OPERATION
IGNITION SWITCH "ON" MODE
When the TBI system is activated by the ignition switch, the
system power relay is energized, and the fuel pump is energized by
the ECU through the fuel pump relay. The pump will operate for
approximately 1 second, unless the engine is operating or the starter
motor is engaged.
The ECU receives input from the CTS, MAT, and MAP sensors.
The up-shift indicator lamp is illuminated.
ENGINE START-UP MODE
When the starter motor is engaged, the ECU receives inputs
from the CTS and speed sensors, the starter motor relay, and the wide
open throttle switch. The fuel pump is activated by the ECU and
voltage is applied to the injector, with the ECU controlling
injection time.
The ECU determines proper ignition timing from the speed
sensor input. If the wide open throttle switch is engaged, the ECU
will deactivate the injector to prevent flooding.
ENGINE WARM-UP MODE
The ECU receives inputs from the CTS, MAT, MAP, speed, and
knock sensors. It also is informed of throttle, gear (automatic
transaxle models) and A/C control position.
The ECU provides a ground for the injector, precisely
controlling fuel delivery to the engine. The ECU also controls
ignition timing, engine idle speed and throttle stop angle. On
vehicles with manual transmissions, the up-shift indicator lamp is
controlled according to engine speed and load.
CRUISE MODE
During cruising speed, the ECU receives inputs from the CTS,
MAT, MAP, EGO, speed and knock sensors. It is also informed of
throttle, gear (automatic transaxle models), and A/C control position.\
The ECU provides a ground to the injector, precisely
controlling injector time. It also controls idle speed, throttle stop
angle, ignition timing, air/fuel mixture ratio and up-shift indicator
lamp.
DECELERATION MODE
During deceleration, the ECU receives inputs from the CTS,

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

\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

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.

CRUIS E C O NTR O L S YSTE M

1988 J e ep C hero ke e
1988 Cruise Control Systems
JEEP CRUISE COMMAND
All Models
DESCRIPTION & OPERATION
Jeep vehicles use an electro-mechanical servo system. The
system consists of a control module, speed sensor, servo, control
switch assembly, vacuum storage canister, check valve and release
system. Release system consists of a mechanical vacuum vent valve and
brake and clutch (M/T) release switches.
Cruise control switch is an integral part of turn signal
switch lever and consists of 2 separate switches. First is an "ON-OFF"
and "RESUME" slide switch located on flat of directional switch lever.
Second is "SET/COAST" push button switch located at end of
directional switch lever. To engage system, move slide switch to "ON"
position and accelerate to desired speed. Depress and release
"SET/COAST" button on end of switch lever. System will now maintain
selected speed.
System will automatically disengage when brake or clutch
pedal is depressed. It can be re-engaged to previously selected speed
by accelerating to 30 MPH and moving slide switch to "RESUME"
position, then releasing switch.
NOTE: When slide switch is moved to "OFF" position, pre-set speed
of "RESUME" function is canceled from memory and must be
reset when system is reactivated.
Higher speed can be set by pressing on accelerator pedal
until new speed is reached and then pushing "SET/COAST" button. Lower
speed can be obtained by lightly depressing brake pedal, allowing the
vehicle to slow to desired speed and then depressing and releasing
"SET/COAST" button.
CONTROL MODULE
Control module receives input voltage representing vehicle
speed from speed sensor, which is driven by the speedometer cable.
Control module has a low speed circuit that prevents operation at
speeds below 30 MPH. See Fig. 1.
SERVO
Servo is controlled by control module and uses manifold
vacuum to control throttle. Bead-link chain connects servo cable to
throttle linkage. See Fig. 1.
CONTROL SWITCH
Control switch assembly is an integral part of turn signal
switch lever. See Fig. 1.
RELEASE SYSTEM
Release system deactivates cruise control system when brake
or clutch pedal is depressed. Either servo vent valve or mechanical
vacuum vent switch admits atmospheric pressure into servo when brake
pedal is depressed.

Fig. 1: Cruise Control System Components
Courtesy of Chrysler Motors.
TROUBLE SHOOTING
NOTE: Vehicles with computerized engine controls, should be tested
for stored computer codes. Codes and related problems must
be repaired prior to cruise control diagnosis and repair.
For additional information, see COMPUTERIZED ENGINE CONTROLS
section.

and cruise control remains inoperative, perform following
adjustments to determine if control module is functional.
1) Remove control module attaching screws or tie straps and
move control module downward for adjustment access. Turn centering
adjustment screw to 10 o'clock position. Turn low speed adjustment
screw to 10 o'clock position. Turn sensitivity adjustment screw fully
clockwise.
CAUTION: Adjustment potentiometers are extremely delicate. Carefully
insert screwdriver and do not push or turn screws
excessively hard. Maximum movement is 3/4 turn.
2) Adjustments are not precisely correct for vehicle, but are
acceptable to determine if control module is functioning. Perform
precise adjustments by road testing vehicle on level road. If
adjustments have no effect on cruise control, replace control module.
3) If actual engagement speed is 2 MPH or more above selected
speed, stop vehicle and turn centering screw 1/16 of a turn
counterclockwise. Recheck engagement speed and adjust as necessary.
4) If engagement speed is 2 MPH or more below selected speed,
turn centering screw 1/16 of a turn clockwise. Recheck engagement
speed and adjust as necessary.
Fig. 2: Control Module Adjustment Screws
Courtesy of Chrysler Motors.
VACUUM VENT VALVE
Depress brake or clutch pedal and hold in depressed position.
Move vacuum vent valve toward bracket on pedal as far as possible.
Release brake or clutch pedal.
TESTING
NOTE: Vehicles with computerized engine controls, should be tested
for stored computer codes. Codes and related problems must
be repaired prior to cruise control diagnosis and repair.
For additional information, see COMPUTERIZED ENGINE CONTROLS
section.
PRELIMINARY INSPECTION
Ensure cruise control wire harness is properly connected to