engine JEEP CHEROKEE 1988 Service Repair Manual

housing with 2 shoulder bolts. Tighten the engine speed sensor
shoulder bolts.
2) Connect the engine speed sensor wire connector.
ELECTRONIC CONTROL UNIT (ECU)
Removal
NOTE: The ECU is located below the instrument panel, between
the steering column and the A/C-Heater housing. See
Fig. 22. Three screws mount the ECU to a bracket.
1) Disconnect the negative battery cable.
2) Remove the 3 ECU attaching screws. See Fig. 23.
3) Disconnect the ECU wiring harness connector.
4) Remove the ECU.
Fig. 22: Location of ECU
Courtesy of Chrysler Motors.

Removal
1) Disconnect the battery negative cable.
2) On vehicles equipped with A/C, remove the electrical
cooling fan and shroud assembly from the radiator to allow room to
rotate the engine with a socket and ratchet using the vibration damper
bolt.
3) Scribe a mark on the distributor housing below the left
side (past) the number one spark plug wire post of the distributor cap\
for reassembly reference for No 1 cylinder firing position.
4) Remove the distributor cap.
5) Turn the engine in a clockwise direction until the rotor
is approaching the scribed mark on the distributor housing. Then
slowly turn the engine until the timing mark on the crankshaft
vibration damper lines up with zero on the front cover timing scale.
See Fig. 24 .
NOTE: The timing mark is located on the edge of the vibration
damper closest to the front cover.
Fig. 24: View of Crankshaft Vibration Damper Timing Marks
Courtesy of Chrysler Motors.
6) Align the trailing edge of the rotor blade with the mark
previously scribed on the distributor housing. See Fig. 25.

Fig. 25: Aligning Rotor & Distributor Cap for Removal
Courtesy of Chrysler Motors.
7) Remove the distributor hold-down bolt and clamp.
8) Remove the distributor from the engine.

Installation
1) If needed, use a flat blade screwdriver to turn the oil
pump gear shaft until the slot is slightly past the 11 o'clock
position. See Fig. 26. The oil pump shaft is located down in the
distributor hole.
Fig. 26: Aligning Oil Pump Gear Shaft
Courtesy of Chrysler Motors.
2) Install the rotor.
3) Without engaging the distributor gear into the cam gear
and ensuring the distributor gasket is installed, position the
distributor into the hole in the engine block.
4) Visually line up the hold down ear of the distributor
housing with the hold down clamp hole. See Fig. 27.
Fig. 27: Installing Distributor
Courtesy of Chrysler Motors.
5) Turn the rotor to the 4 o'clock position. See Fig. 28.

Electronic Spark Timing (EST) is used on most computer
controlled systems. The Electronic Control Module (ECM) monitors
information from various engine sensors, computes desired spark
timing, and signals distributor for correct timing change. The HEI
distributor with EST does not have centrifugal advance weights,
springs, or a vacuum advance unit. See Figs. 2 and 3.
HEI & EST WITH ELECTRONIC SPARK CONTROL (ESC)
All fuel injected vehicles are equipped with Electronic Spark
Control (ESC). ESC systems contain a knock sensor mounted in the
engine block. A Blue wire connects the sensor to the ESC module. If
the sensor detects knock, it sends a signal to the module which, in
turn, signals the ECM. The ECM sends a signal to the distributor to
retard spark timing.
Fig. 2: Typical HEI/EST Distributor, Integral coil system shown.
Courtesy of General Motors Corp.
OPERATION

The ECM monitors information concerning crankshaft position,
engine RPM, engine load, atmospheric conditions, engine temperature,
and transmission gear position. This information is used by the ECM to
compute desired spark timing which is relayed to the distributor,
enabling appropriate changes to be made to ignition timing. A back-up
spark advance system is incorporated to signal ignition module in the
event of ECM failure.
CAUTION: Although similar in appearance, components of HEI/EST and
HEI distributors are NOT interchangeable.
All Models With EST
The distributor module is connected to ECM by a 4-wire EST
connector which performs the following functions:
* Terminal "A" of the 4-wire connector is the reference ground
low. It is grounded in the distributor and ensures ground
circuit does not have a voltage drop. If circuit is open,
engine may experience poor performance.
* Terminal "B" of the 4-wire connector is the by-pass circuit.
At about 400 RPM, ECM applies 5 volts to this circuit to
switch spark timing control from module to ECM. An open or
grounded by-pass circuit will set a code 42 and the engine
will operate at base timing, plus a slight amount of advance
built into the module.
* Terminal "C" is the distributor reference High circuit. This
circuit provides the ECM with RPM and crankshaft position
information.
* Terminal "D" is the EST circuit, which triggers the module.
The ECM does not know what actual timing is, but does know
when it receives the reference signal. It will advance or
retard spark from that point. If base timing is set
incorrectly, engine spark curve will be incorrect.
SENSORS
On EST systems, the coolant temperature sensor signals ECM to
advance timing on a cold engine and return timing to programmed
advance curve as engine reaches normal operating temperature. If
engine overheats, spark is retarded to prevent detonation. During
light throttle operation, throttle position sensor input to ECM allows
for additional advance.
Spark advance is also governed by input from engine RPM and
Manifold Absolute Pressure (MAP) sensor. When MAP output voltage is
low (high vacuum), ECM gives less spark advance. More spark advance is\
given when MAP output voltage is high (low vacuum).
ELECTRONIC SPARK CONTROL (ESC) SYSTEM
All Fuel Injected Engines
The basic components of Electronic Spark Control (ESC) system\
are detonation (knock) sensor, HEI/EST distributor, ESC module and
ECM. When detonation (knock) occurs, sensor sends an electrical signal\
to ESC module. The ESC module then sends the signal voltage to the
ECM. When the ECM senses a voltage drop (to less than one volt) on the\
knock sensor signal line, spark timing will be retarded. The ECM will
retard spark timing until all signals from detonation sensor cease.
See Fig. 4 .

Fig. 4: Circuit Diagram of HEI/EST Ignition System
Courtesy of General Motors Corp.
ADJUSTMENTS
The only adjustments that can be made to HEI/EST igntion
system are basic ignition timing and spark plug gap.
DIAGNOSIS
If reference or EST signals are interrupted due to an open
circuit or a faulty ECM, HEI/EST module will provide a timing signal
based on engine RPM. Engine may continue to run, although less
efficiently. If by-pass signal is lost, by-pass switch will direct RPM
information directly to coil rather than to ECM.
Normally, 5-15 seconds after starting a warm engine, by-pass
signal from ECM will operate a by-pass switch in HEI/EST module. The
HEI/EST module's RPM-controlled timing signal will switch over and RPM
signal will flow directly to the ECM for processing.
Loss of EST signal from ECM when 5-volt by-pass signal is
present will cause engine to stop because HEI/EST module is no longer
sending signals directly to ignition coil. Any loss of EST signal will
stop all flow to coil. If vehicle is restarted, engine will run for a
few seconds and stop when by-pass signal comes back on.
COMPONENT TESTING (HEI)
ELECTRONIC MODULE
NOTE: Testing applies to HEI systems with mechanical weights and
vacuum advance only.
1) An approved electronic module tester must be used to test
the module. Use Module Tester (J-24642-E). Follow manufacturer's
instructions.
2) When installing a new HEI control module, use silicone

system. For testing, see appropriate IGNITION SYSTEM CHECK
flow chart in COMPUTERIZED ENGINE CONTROLS section. For
diagnosis of HEI system, refer to following diagnostic
chart. See Fig. 11.
Fig. 11: Ignition Sys Check (HEI Only), Testing applies to HEI
sys with mechanical weights and vacuum advance.
Courtesy of General Motors Corp.
OVERHAUL

MAIN TE N AN CE IN FO RM ATIO N

1988 J e ep C hero ke e
1984-88 MAINTENANCE
AMC/Jeep Maintenance Information
Jeep; Cherokee,
Wagoneer
* PLEASE READ THIS FIRST *
NOTE: For scheduled maintenance intervals and the related fluid
capacities, fluid specifications and labor times for major
service intervals, see SCHEDULED SERVICES article below:
* SCHEDULED SERVICES - GASOLINE
* SCHEDULED SERVICES - DIESEL ENGINES - NORMAL (1985-87)
Warranty information and specifications for fluid
capacities, lubrication specifications, wheel and tire size,
and battery type are covered in this article.
MODEL IDENTIFICATION
VIN LOCATION
The Vehicle Identification Number (VIN) is located on the
left side of the dash panel at the base of the windshield. The VIN
chart explains the code characters.
VIN CODE ID EXPLANATION
Numbers preceding the explanations in the legend below refer
to the sequence of characters as listed on VIN identification label.
See VIN example below.








\









\









\









\









\









\








 
(VIN) 1 J C U N 7 7 1 X G T 0 0 0 0 0 1 


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 










\









\









\









\









\









\








1 - Manufacturing Country
1
* United States
2 - Company/Make
J * American Motors/Jeep
3 - Type
C * Multi-Purpose Vehicle
D * Incomplete Vehicle
E * Export, LHD
F * Export, RHD
4 - Engine Type
B * 2.1L (128 CID) 4-Cylinder Turbo (Diesel) (001B) (1985-87)
H * 2.5L (150 CID) 4-Cylinder TBI (Gasoline) (001H) (1986-88)
U * 2.5L (150 CID) 4-Cylinder 1-Bbl. (Gasoline) (001U) (1984-85)
Y * 2.5L (150 CID) 4-Cylinder 1-Bbl. (Export) (001Y) (1984-85)
W * 2.8L (171 CID) V6 2-Bbl. (Gasoline) (001W) (1984-86)
M * 4.0L (242 CID) I-6 (Gasoline) (001M) (1987-88)

* Cold Climate Operation
* Towing Or Heavily Loading
* Severe Dust Conditions
* Sustained High Speed Operation
* Off-Road Driving
* Hot Weather, Stop-And-Go Driving
* Extensive Idling Conditions (Taxi Or Delivery Type Service)
Normal Service
* Driven More Than 10 Miles Daily
* No Severe Service Operating Conditions
CAMSHAFT TIMING BELT REPLACEMENT INFORMATION (TURBO-DIESEL)
CAUTION: Failure to replace a faulty camshaft timing belt may result
in serious engine damage.
The condition of camshaft drive belts should always be
checked on vehicles which have more than 50,000 miles. Although some
manufacturers do not recommend belt replacement at a specified
mileage, others require it at 60,000-100,000 miles. A camshaft drive
belt failure may cause extensive damage to internal engine components
on most engines, although some designs do not allow piston-to-valve
contact. These designs are often called "Free Wheeling".
Many manufacturers changed their maintenance and warranty
schedules in the mid-1980's to reflect timing belt inspection and/or
replacement at 50,000-60,000 miles. Most service interval schedules
reflect these changes.
Belts or components should be inspected and replaced if any
of the following conditions exist:
* Cracks Or Tears In Belt Surface
* Missing, Damaged, Cracked Or Rounded Teeth
* Oil Contamination
* Damaged Or Faulty Tensioners
* Incorrect Tension Adjustment
SERVICE LABOR TIMES
SERVICE LABOR TIMES TABLE (HOURS)








\









\









\









\









\









\









\



( 1) 30,000 60,000
Application Mile Service Mile Service
2.1L (Turbo Diesel)
Automatic Transmission ........... 4.3 ................ 4.5
Manual Transmission .............. 3.6 ................ 3.8
2.5L
Automatic Transmission ........... 5.6 ................ 3.5
Manual Transmission .............. 4.9 ................ 3.5
2.8L
Automatic Transmission ........... 5.8 ................ 3.7
Manual Transmission .............. 5.1 ................ 3.7
4.0L
Automatic Transmission ........... 5.7 ................ 3.6
Manual Transmission .............. 5.0 ................ 3.6
( 1) - Add .8 hr. for vehicles equipped with 4WD.









\









\









\









\









\









\









\