6 CYLINDER JEEP CHEROKEE 1988 JEEP CHEROKEE 1988 Service Repair Manual

\003
2.5 L 4 -C YL - V IN [ H ]

1 988 J e ep C hero ke e
1988 CHRYSLER MOTORS ENGINES
2.5L 4-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 the
upper left side of dash, visible through windshield. The fourth
character of the VIN identifies the engine size. The tenth character
identifies the model year.
ENGINE IDENTIFICATION CODES TABLE









\









\









\









\









\









\






Application VIN Code
2.5L 4-Cylinder TBI .................................... H









\









\









\









\









\









\






SPECIAL ENGINE MARKS
Some engines are produced at the factory with oversize or
undersize components. These engines are identified by a letter code
stamped between ignition coil and distributor. Letters are decoded as
follows:
* "B" indicates all cylinder bores .010" (.25 mm) oversize.
* "C" indicates all camshaft bearing bores .010" (.25 mm)
oversize.
* "M" indicates all main bearing journals .010" (.25 mm)
undersize.
* "P" indicates all connecting rod journals .010" (.25 mm)
undersize.
REMOVAL & INSTALLATION
ENGINE REMOVAL
See ENGINE REMOVAL article.
INTAKE & EXHAUST MANIFOLDS
NOTE: Throttle body removal is necessary prior to manifold
removal. Throttle body can be separated from the manifold
and secured in a designated area with vacuum hoses attached.
Removal
1) Disconnect negative battery cable. Remove air cleaner, EGR
pipe and PCV hose. Disconnect and mark all vacuum hoses and electrical
connections. Drain cooling system.
2) Remove coolant hoses from intake manifold. Remove A/C
compressor and power steering pump and mounting bracket (if equipped).\

\0032.5 L C EC S YSTE M

1988 J e ep C hero ke e
1988 Computerized Engine Controls
JEEP 4-CYLINDER 2.5L TBI COMPUTERIZED EMISSION CONTROL
Cherokee, Comanche
DESCRIPTION
The computerized engine control system, used on 2.5L models
with throttle body fuel injection, is built around an electronic
control unit (ECU). The ECU is a microprocessor-based computer.
The major function of the system is to reduce emissions. It
accomplishes this through a series of 13 sensors or switches that
constantly monitor several engine conditions. See Fig. 16.
Fig. 1: Vacuum Diagram for Jeep 2.5L CEC System
The computer processes input information from the sensors to
get an accurate picture of engine operation. It then provides output
control signals to regulate air/fuel ratio, ignition, idle speed and

\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









\









\









\









\









\




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









\









\









\









\









\




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

\003
4.0 L C EC S YSTE M

1988 J e ep C hero ke e
1988 COMPUTERIZED ENGINE Controls
ENGINE CONTROL SYSTEM
JEEP 4.0L MPFI 6-CYLINDER
Cherokee, Comanche & Wagoneer
DESCRIPTION
The 4.0L engine control system controls engine operation to
lower exhaust emissions while maintaining good fuel economy and
driveability. The system is designed to maintain a 14.7:1 air/fuel
ratio under all engine operating conditions. When the ideal air/fuel
ratio is maintained, the catalytic converter can control oxides of
nitrogen (NOx), hydrocarbon (HC), and carbon monoxide (CO) emissio\
ns.
The system consists of the following sub-systems: Fuel
Control, Data Sensors and Switches, Electronic Control Unit (ECU),
Diagnostics, Electronic Spark Advance, Idle Speed Control, Exhaust Gas
Recirculation, and Transmission Shift Light.
OPERATION
FUEL CONTROL
The fuel control system delivers fuel to the engine. Fuel
from the in-tank fuel pump flows to the fuel rail, injectors and
pressure regulator. The pressure regulator maintains fuel system
pressure at 31-39 psi (2.l-2.7 kg/cm
). Excess fuel is returned to the
tank by a fuel return line.
The fuel pump is energized through the fuel pump relay that
is located on the right inner fender panel in the engine compartment.
Battery voltage is provided through the ignition switch and is
energized when the ECU completes the ground path.
The fuel injectors are electrically operated solenoid valves.
The ECU determines injector pulse width ("on/off") time based upon
engine operating conditions and delivers the proper pulse width to
maintain an air/fuel ratio of 14.7:l.
The ECU varies the amount of voltage applied to the injectors
to compensate for battery voltage changes. Battery voltage information
is provided to the ECU through the wiring harness. No sensor or switch
is required.
DATA SENSORS & SWITCHES
Each sensor and/or switch furnishes electronic impulses to
the ECM. Based on these input signals, the ECM computes spark timing
and air/fuel mixture for proper engine operation.
Coolant Temperature Sensor (CTS)
The CTS is located on the left side of the block, just below
exhaust manifold. The sensor provides coolant temperature information
to the ECU. Engine coolant temperature is used by the ECU for the
following functions:
* Enrich air/fuel mixture for cold engine starts.
* Control idle speed during warm-up.
* Increase spark advance during cold engine operation.
* Prevent EGR flow during cold engine operation.

BRAK E S YSTE M B LE ED IN G

1988 J e ep C hero ke e
1988 BRAKES
Jeep - Brake System Bleeding
Cherokee, Comanche, Grand Wagoneer, Wagoneer, Wrangler
BRAKE SYSTEM BLEEDING
Hydraulic system bleeding is necessary any time air has been
introduced into system. Bleed brakes at all 4 wheels if master
cylinder lines have been disconnected or master cylinder has run dry.
Bleed brakes with vacuum bleeding equipment, pressure bleeding
equipment or by manually pumping brake pedal while using bleeder
tubes. Always bleed brake lines in sequence. See BLEEDING SEQUENCE
table.
MASTER CYLINDER BLEEDING
Bench Bleeding
1) Master cylinder must be bled before installation to
prevent excessive amounts of air from entering the brake system,
creating poor brake operation.
2) Place master cylinder in soft-jawed vise. DO NOT tighten
vise enough to damage master cylinder. Install bleeder tubes in both
outlets of master cylinder. See Fig. 1.
Fig. 1: Bleeding Master Cylinder
Courtesy of American Motors/Jeep Corp.
3) Fill master cylinder with clean brake fluid that meets DOT
3 specifications. Ensure that the end of bleeder tubes are submerged

BRAK E S YSTE M

1988 J e ep C hero ke e
1988 BRAKES
Jeep - Brake System
Cherokee, Comanche, Grand Wagoneer, Wagoneer, Wrangler
DESCRIPTION
DISC BRAKES
Floating caliper disc brake assembly uses a single piston
caliper which "floats" on 2 bolts. As brake pedal is depressed,
hydraulic pressure is passed through a proportioning valve to brake
caliper piston.
This force is transmitted to inboard brake pad, forcing it
against braking surface of rotor. Pressure then moves outer caliper
housing and pad inward on caliper mounting bolts, thus forcing outer
pad against outer braking surface of rotor.
DRUM BRAKES
Self-centering type system uses primary and secondary brake
shoes with cable operated automatic adjusters. Brake shoe anchor is
located at upper end of shoes above wheel cylinder. Single double
acting brake cylinder is used.
MASTER CYLINDER - EXCEPT GRAND WAGONEER
The Delco Quick Take-Up master cylinder is used with systems
utilizing low drag calipers. Master cylinder includes a quick take-up
valve which delivers a large volume of fluid, at low pressure, upon
initial brake application.
MASTER CYLINDER - GRAND WAGONEER
Bendix and Delco-Moraine tandem dual piston master cylinders
are single casting type with front and rear pistons and a separate
reservoir and outlet for each piston. Primary piston is operated by
push rod connected to brake pedal. Secondary piston is operated by
primary piston.
ADJUSTMENTS
NOTE: For Hub, Bearing and Axle Shaft Removal, Installation and
Adjustment information, see appropriate DRIVE AXLES article.
DISC BRAKE PADS
Automatic adjustment is provided by outward relocation of
piston as lining wears.
DRUM BRAKE SHOES
1) Rear brake shoes adjust automatically as brakes are
applied while vehicle is operated in reverse. Drive vehicle in reverse
applying brakes firmly 10-15 times, between each reverse brake
application, drive vehicle forward and press brakes firmly.
2) Manual adjustment is required if shoes have been removed

CEC C O M PO NEN T R EM OVA L & IN STA LLA TIO N

1988 J e ep C hero ke e
1984-86 Computerized Engine Controls
JEEP 4-CYLINDER COMPUTERIZED ENGINE CONTROL
COMPONENT REMOVAL & INSTALLATION
Cherokee, CJ/Scrambler, Comanche, Wagoneer, Wrangler
MICROCOMPUTER CONTROL UNIT (MCU) R & I
The MCU is located behind the right front kick panel. Remove
MCU mounting bolts and disconnect wiring harness connector. Do not
bend connector pins when removing. Reconnect harness to MCU and
replace mounting bolts.
MIXTURE CONTROL (M/C) SOLENOID R & I
Remove air cleaner and disconnect solenoid harness connector.
Remove retaining screws and remove solenoid from carburetor. Coat
rubber seal, on end of solenoid stem, with silicone grease or light
engine oil prior to reinsertion. Using a new gasket, replace solenoid.
Reconnect wiring harness and replace air cleaner.
Fig. 1: M/C Solenoid Location on Carburetor
OXYGEN (O2) SENSOR R & I

\003
* D RIV ETR AIN S YSTE M S U NIF O RM IN SPEC TIO N G UID ELIN ES *
1988 Jeep Cherokee
GENERAL INFORMATION
Drivetrain/Transmission Motorist Assurance Program
Standards For Automotive Repair
All Makes and Models
INTRODUCTION TO MOTORIST ASSURANCE PROGRAM (MAP)
CONTENTS
OVERVIEW OF MOTORIST ASSURANCE PROGRAM
OVERVIEW OF SERVICE REQUIREMENTS & SUGGESTIONS
Drive/Power Train Assemblies
AUTOMATIC TRANSMISSION/TRANSAXLE ASSEMBLIES
DIFFERENTIAL AND FINAL DRIVE ASSEMBLIES
MANUAL TRANSMISSION/TRANSAXLE ASSEMBLIES
TRANSFER CASE ASSEMBLIES
Drive/Power Train Components
ACTUATORS (ELECTRICAL)
ACTUATORS (VACUUM)
AXLES
BEARINGS AND RACES
BELL CRANKS
BELL HOUSINGS
BUSHINGS (EXTERNAL)
CABLES (SPEEDOMETER)
CABLES (TV, DETENT AND SHIFT)
CARRIER BEARINGS
CLUTCH CABLES AND CABLE HOUSINGS
CLUTCH DISCS (MANUAL TRANSMISSION)
CLUTCH FORKS
CLUTCH LINKAGES (MECHANICAL)
CLUTCH MASTER CYLINDERS
CLUTCH PEDALS
CLUTCH PIVOTS
CLUTCH PRESSURE PLATES
CLUTCH RELEASE BEARINGS
CLUTCH SLAVE CYLINDERS (CONCENTRIC)
CLUTCH SLAVE CYLINDERS (CONVENTIONAL OR EXTERNAL)
COMPANION FLANGES
CONNECTORS
COOLER BYPASS VALVES
COOLER LINES
COOLERS
CV JOINTS
DIP STICK TUBES
DIP STICKS (FLUID LEVEL INDICATORS)
DOWEL PINS, GUIDES AND PILOT HOLES
DRIVE SHAFT FLANGES
DRIVE SHAFTS AND HALF SHAFTS
DUST BOOTS
ENGINE MOUNTS
EXCITER RINGS
FILLER TUBES
FILTERS AND SCREENS

\003
EN G IN E R EM OVA L - 4 -C YL

1988 J e ep C hero ke e
1988 ENGINES
Jeep - Engine Removal - 4-Cylinder
Cherokee, Comanche, Wrangler
4-CYLINDER ENGINES
2.5L
1) Disconnect negative battery cable. Drain cooling system.
Remove air cleaner, lower radiator hose, fan shroud, and engine
compartment light from hood. Scribe hinge locations and remove hood.
Disconnect automatic transmission cooler lines at radiator (if
equipped).
2) Remove upper radiator hose, fan assembly and coolant
recovery hose. Remove radiator and A/C condenser (if equipped). Hold
fan pulley to water pump flange using 5/16" x 1/2" SAE capscrew.
Disconnect heater hoses, throttle linkages, cruise control cable (if
equipped) and Throttle valve rod.
3) Disconnect wires from starter and separate CEC system
wiring harness connector. Disconnect fuel pipe from fuel pump and fuel
return hose from fuel filter. Disconnect hoses from A/C compressor and
power steering pump (if equipped). Drain power steering pump
reservoir. Cap all fittings and hose ends.
4) Remove vacuum check valve from brake booster (if
equipped). Tag and remove all wiring and vacuum lines connected to
engine or accessories. Raise vehicle and remove starter. Disconnect
exhaust pipe from manifold.
5) Remove converter/flywheel housing cover. Remove engine
mount nuts at bracket side. On automatic transmission models, index
mark drive plate and torque converter. Remove drive plate-to-converter
bolts.
6) Remove upper and loosen lower bellhousing-to-engine bolts.
Attach lifting equipment to engine. Raise engine off front mounts,
Place support under bellhousing. Remove remaining bellhousing-to-
engine bolts. Lift engine out of engine compartment.
NOTE: Engine mount pads may be removed from engine brackets to
align engine and transmission during installation.
TORQUE SPECIFICATIONS
TORQUE SPECIFICATIONS TABLE








\









\









\









\









\









\






Application Ft. Lbs. (N.m)
Clutch Housing-to-Block Bolts .................... 55 (75)
Drive Plate-to-Converter ......................... 26 (35)
Flywheel Bolts ............................... ( 1) 50 (68)
Front Support Bracket-to-Block ................... 45 (61)
Front Support Cushion-to-Crossmember ............. 33 (45)
Rear Support Bracket-to-Transmission ............. 33 (45)
Rear Support Cushion-to-Bracket .................. 30 (41)
Starter Motor-to-Block ........................... 33 (45)
( 1) - Tighten an additional 60 degrees.









\









\









\









\









\









\

\003
EN G IN E R EM OVA L - 6 -C YL

1988 J e ep C hero ke e
1988 ENGINES
Jeep - Engine Removal - 6-Cylinder
Cherokee, Comanche, Wagoneer, Wrangler
6-CYLINDER ENGINES
4.0L
1) Scribe hinge locations, remove engine compartment light
(if equipped) and remove hood. Disconnect battery cables and remove
battery. Drain cooling system.
2) Disconnect wire connectors from alternator, ignition coil
and distributor. Disconnect oil pressure sender wire, starter wires
and fuel injector wiring harness (if equipped). Detach 2 fuel pipe
quick connect couplings at left inner fender panel. Disconnect engine
ground strap and remove air cleaner.
3) Disconnect the vacuum purge hose at fuel vapor canister
tee. Disconnect wire from idle speed actuator and oxygen sensor.
Detach throttle cable from bracket and disconnect throttle valve rod
at bellcrank. Remove upper and lower radiator hoses.
4) On automatic transmission models, disconnect the
transmission fluid cooler tubing. On all models, remove fan shroud and
radiator. Remove fan and spacer or Tempatrol fan assembly. Hold fan
pulley to water pump flange using 5/16" x 1/2" SAE capscrew while
crankshaft is rotated.
5) Disconnect cruise control cable (if equipped). Disconnect\
wires from starter motor solenoid and disconnect CEC system harness.
Remove power brake vacuum check valve from booster (if equipped).
6) Disconnect power steering hoses from steering gear (if
equipped). Drain power steering pump reservoir and plug end of hoses.
Cap all fittings on steering gear and hoses. Raise and support
vehicle. Remove starter. Remove flywheel housing access cover.
7) Remove upper and loosen lower bellhousing-to-engine bolts.
Attach lifting equipment to engine. Raise engine off front mounts.
Place support under bellhousing. Remove remaining bellhousing-to-
engine bolts. Lift engine out of engine compartment.
4.2L
1) Remove battery and drain cooling system. Remove air
cleaner and engine compartment light from hood. Scribe hinge location
and remove hood. Disconnect and plug front fuel line at pump and fuel
return line at frame.
2) Disconnect heater hoses at heater. Label and disconnect
all wiring, lines, linkage and hoses at engine. Remove vacuum switch
assembly bracket from cylinder head cover. Remove both radiator hoses
and automatic transmission oil lines (if equipped) at radiator. Remove\
radiator and shroud.
3) Remove fan and spacer. Use 5/16" x 1/2" SAE bolt to hold
fan pulley to water pump flange. Remove starter and disconnect engine
ground strap. Remove engine mount-to-bracket nuts. Disconnect exhaust
pipe at manifold.
4) Discharge A/C system (if equipped). Disconnect and plug
hose or port openings at compressor. Disconnect hoses at power
steering gear and drain reservoir. Remove power brake vacuum check
valve. Remove bracket bolt for automatic transmission filler tube (if
equipped).
5) Lift and support vehicle. On models with automatic