warning JEEP CHEROKEE 1988 Service Repair Manual

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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

CAN TAP INSTALLATION
FLAT TYPE SEAL CANS
On cam-lock or one-piece can taps, first turn the handle out
to the fully open position. Securely engage the locking lugs over the
flange of the can, and lock them in place by turning the cam lock or
locking nut. Screw the tap assembly into the adapter so the sealing
gasket is fully seated against the can top. Turn the tap inward to
pierce the can and close the tap. DO NOT open the tap until ready to
purge the service hose or dispense refrigerant into the system.
On 2-piece can taps, be certain the tap handle is turned
fully in, so it is closed. Check that the locking base is turned to
its outer limit. Securely engage the locking lugs over the can
flange. Turn the entire tap assembly (without disturbing the closed
setting) down into the locking base to pierce the can. Do not open
the tap until ready to dispense into system.
SCREW TYPE SEAL CANS
Ensure can tap is fully closed. Screw refrigerant can into
can tap fitting until tight. This will pierce the can. Connect tap to
center hose on manifold gauge set. DO NOT open tap until ready to
dispense R-12 into system.
WARNING: DO NOT open high side hand valve while air conditioning
system is in operation. This high pressure could rupture
can or possibly burst fitting at safety can valve,
resulting in damage and physical injury.
COMPRESSOR OIL CHECK
GENERAL PROCEDURES
Some models have compressor-mounted service valves that allow
oil checking by isolating the compressor. On all others, system must
be discharged, using approved refrigerant recovery/recycling
equipment, and compressor may need to be removed to check oil. After
oil level is checked and adjusted, A/C system must be evacuated and
recharged.
ISOLATING COMPRESSOR
1) Connect manifold gauge set to service valves on the
compressor. Close both gauge valves. Open both service valves to
themid-position.
2) Start engine and operate air conditioning. Turn suction
service valve slowly clockwise toward front-seated position. When
suction pressure is reduced to zero or less, stop engine and quickly
close suction service valve (front-seated).
3) Front-seat the discharge valve. Loosen oil check plug
slowly to release any internal pressure. Service valves can now be
removed from compressor and compressor removed from vehicle (if
necessary). Purge compressor after servicing.
PURGING COMPRESSOR
1) Remove gauge set and place caps on service valve ports.
Back-seat the suction service valve to allow refrigerant to enter
compressor.

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AN TI- L O CK B RAK E S A FE TY P R EC AU TIO NS

1988 J e ep C hero ke e
GENERAL INFORMATION
Anti-Lock Brake Safety Precautions
* PLEASE READ THIS FIRST *
This article is intended for general information purposes
only. This information may not apply to all makes and models. If
vehicle is equipped with Anti-Lock Brake System (ABS), refer to
appropriate ANTI-LOCK BRAKE SYSTEM article in the BRAKES section for
description, operation, depressurizing, testing, system bleeding,
trouble shooting and servicing of specific system.
WARNING: Failure to depressurize ABS could lead to physical injury.
ANTI-LOCK BRAKE SAFETY PRECAUTIONS
WARNING: Failure to depressurize ABS could lead to physical injury.
* NEVER open a bleeder valve or loosen a hydraulic line
while ABS is pressurized.
* NEVER disconnect or reconnect any electrical connectors
while ignition is on. Damage to ABS control unit may result.
* DO NOT attempt to bleed hyudarulic system without first
referring to the appropriate ANTI-LOCK BRAKE SYSTEM article
in the BRAKES section.
* Only use specially designed brake hoses/lines on ABS equipped
vehicles.
* DO NOT tap on speed sensor components (sensor, sensor rings).
Sensor rings must be pressed into hubs, NOT hammered into
hubs. Striking these components can cause demagnetization or
a loss of polarization, affecting the accuracy of the speed
signal returning to the ABS control unit.
* DO NOT mix tire sizes. Increasing the width, as long as tires
remain close to the original diameter, is acceptable. Rolling
diameter must be identical for all 4 tires. Some
manufacturers recommend tires of the same brand, style and
type. Failure to follow this precaution may cause inaccurate
wheel speed readings.
* DO NOT contaminate speed sensor components with grease. Only
use recommended coating, when system calls for an
anti-corrosion coating.
* When speed sensor components have been removed, ALWAYS check
sensor-to-ring air gaps when applicable. These specifications
can be found in each appropriate article.
* ONLY use rocommended brake fluids. DO NOT use silicone brake
fluids in an ABS equipped vehicle.
* When instlling transmittion devices (CB's, telephones, etc.)
on ABS equipped vehicles, DO NOT locate the antenna near the
ABS control unit (or any control unit).
* Disconnect all on-board computers, when using electric
welding equipment.
* DO NOT expose the ABS control unit to prolonged periods of
high heat (185
F/85C for 2 hours is generally considered a
maximum limit).

and make an informed decision about how to proceed.
BRAKES
SERVICE PROCEDURES REQUIRED & SUGGESTED FOR PROPER
VEHICLE OPERATION
Some states may have specifications that differ from OEM.
Check your local/state regulations. Where state or local laws are
stricter, they take precedence over these guidelines.
ACCELEROMETERS (G SENSOR OR LATERAL)
ACCELEROMETER INSPECTION








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Condition Code Procedure
Broken .................. A ............ Require replacement.
Connector loose ......... A .. Require repair or replacement.
Loose ................... B .. Require repair or replacement.
Missing ................. C ............ Require replacement.
Out of position ......... B ....... Require re-positioning to
vehicle manufacturer's
specifications.
Output signal incorrect . B ............ Require replacement.









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ACCUMULATORS
ACCUMULATOR INSPECTION








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Condition Code Procedure
Leaking ................. B ............ Require replacement.
Missing ................. C ............ Require replacement.
Pre-charge incorrect .... B ............ Require replacement.









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ANCHOR PINS
See BACKING PLATES .
ANTI-LOCK BRAKE SYSTEMS
NOTE: Anti-lock brakes are an integral part of the brake system. It
is essential that the anti-lock brakes function properly when
brake service is performed.
Anti-lock brake systems are commonly referred to as "ABS" and
will be referred to as "ABS" throughout these guidelines. Some ABS
components also function as part of a traction control system (TCS).
WARNING: When diagnosing and servicing high pressure components,
observe safety procedures and equipment requirements
established by the vehicle manufacturer to reduce the
possibility of serious personal injury.
NOTE: Intermittent electrical conditions are often caused by a loss
of ground, poor connection, or water intrusion into the
wiring harness.

Automatic Load Leveling Sw. On compressor bracket, in
engine compartment.
Back-Up Light Sw. (Man. Trans.) On left side of transmission
case.
Back-Up/Neutral Sw. (Auto. Trans.) On left side of transmission
case.
Brake/Stop Light (Cruise) Switch On brake pedal bracket.
Brake Warning Switch On brake pressure differential
valve, below master cylinder.
Closed Throttle (Idle) Switch An integral part of ISA motor.\
Command Track Switch On left side of transmission.
Parking Brake Switch Under center console, at base
of parking brake lever.

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ELE C TR O STA TIC D IS C HAR G E W AR NIN G - B ASIC IN FO RM ATIO N
1988 J e ep C hero ke e
GENERAL INFORMATION
Electrostatic Discharge (ESD) Warning - Basic Information
All Makes amd Models
* PLEASE READ THIS FIRST *
NOTE: This article is intended for general information purposes
only.
INTRODUCTION
All Electrostatic Discharge (ESD) sensitive components
contain solid state circuits (transistors, diodes, semiconductors)
that may become damaged when contacted with an electrostatic charge.
The following information applies to all ESD sensitive devices. The
ESD symbol shown in Fig. 1 may be used on schematics to indicate which
components are ESD sensitive. See Fig. 1. Although different
manufactures may display different symbols to represent ESD sensitive
devices, the handling and measuring precautions and procedures are the
same.
Fig. 1: Sample ESD Symbol
HANDLING STATIC-SENSITIVE CIRCUITS/DEVICES

Fig. 1: Oxygen Sensor Location
B. Replace Catalytic Converter
WARNING: IF TORCHES ARE USED WHEN WORKING ON THE EXHAUST SYSTEM,
DO NOT ALLOW THE FLAME NEAR THE FUEL LINES.
1. Remove and discard the nuts, bolts and gasket at the front of the
converter and the exhaust pipe clamp at the rear (see Fig. 2).
NOTE: Use penetrating oil if necessary.

1 - Part is close to the end of its useful life (just above
discard specifications, or weak; failure likely to occur
soon, etc.)
2 - To address a customer need, convenience, or request (to
stiffen ride, enhance performance, eliminate noise,
etc.)
3 - To comply with maintenance recommended by the vehicle's
Original Equipment Manufacturer (OEM)
4 - Technician's recommendation based on substantial and
informed experience
NOTE: Suggested services are always optional. When presenting
suggested repairs to the customer, you must present
the facts, allowing the customer to draw their own
conclusions and make an informed decision about how to
proceed.
EXHAUST
SERVICE PROCEDURES REQUIRED AND SUGGESTED FOR PROPER
VEHICLE OPERATION
WARNING: Federal EPA rules prohibit altering an exhaust system in
any way that defeats the emission reduction components of a
vehicle. Be sure to review and adhere to EPA policy on
removing and replacing catalytic converters. Where state or
local laws are stricter, they take precedence over these
guidelines.
NOTE: Some exhaust systems are of a welded design. It is not
required that the entire system be replaced. Determine the
need to replace individual components based on conditions of
component.
CATALYTIC CONVERTERS
CAUTION: Before working on an exhaust system, review EPA
regulations on removing and replacing catalytic converters.
NOTE: Any time a converter has failed, further diagnosis is
required to determine the reason(s) for converter failure.
CATALYTIC CONVERTER INSPECTION









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Condition Code Procedure
Air injection tube
broken ................. A ... Require repair or replacement
of injection tube or
replacement of catalytic
converter.
Air injection tube
burnt .................. A ... Require repair or replacement
of injection tube or
replacement of catalytic
converter.
Air injection tube
leaking ................ A ... Require repair or replacement
of injection tube or
replacement of catalytic
converter.
Air injection tube

* Battery connections and specific gravity.
* Engine Compression.
* Electrical connections on components and sensors.
* Emission control devices.
* Ignition system.
* All vacuum line, fuel hose and pipe connections.
General Precautions
In order to prevent injury to operator or damage to system
or component parts, use following techniques:
* Turn ignition off before connecting or disconnecting any
component parts.
* DO NOT apply DC voltage greater than 12 volts or any AC voltage
to system.
* Disconnect battery cables before charging.
* Remove ECU from vehicle if ambient temperature could exceed
176

F (80
C).
* DO NOT modify or circumvent any system functions.
SYSTEM TESTING
Fuel System Test
WARNING: Always relieve residual fuel pressure in fuel delivery
system before opening system. To prevent chance of personal
injury, cover fittings with shop towel while disconnecting
fittings.
1) Remove cap from pressure test port located in fuel rail.
See Fig. 3 . Connect Fuel Pressure Gauge (J-34730-1) to pressure
fitting.
2) Start vehicle. Pressure should be approximately 31 psi
(2.1 kg/cm
) with vacuum hose connected to pressure regulator and
39 psi (2.6 kg/cm) with vacuum hose removed from pressure
regulator.
3) Check fuel pump flow rate. A good fuel pump will deliver
at least one liter of fuel per minute with fuel return line pinched
off. If fuel pump does not pump adequately, inspect fuel system for a
plugged fuel filter or filter sock.
Fig. 3: Fuel System Pressure Test Components
Courtesy of Chrysler Motors.
4) Fuel pump flow rate can be checked by connecting one end
of an old A/C gauge hose to fuel test port on fuel rail and inserting

See FUEL INJECTOR TEST PROCEDURE chart in this article.
REMOVAL & INSTALLATION
COOLANT TEMPERATURE SENSOR (CTS)
Removal & Installation
Drain cooling system. Remove air cleaner assembly.
Disconnect CTS wire connector. Remove CTS from engine block. Install
replacement CTS and connect CTS wire connector. Install air cleaner
assembly. Fill cooling system.
OXYGEN SENSOR
Removal & Installation
Raise and support vehicle. Disconnect O2 sensor wire
connector. Remove O2 sensor from exhaust manifold. Install O2 sensor
and tighten to 30 ft. lbs. (41 N.m). Connect O2 sensor wire connector
and lower vehicle.
KNOCK SENSOR
Removal & Installation
Raise and support vehicle. Disconnect knock sensor wire
connector. Remove knock sensor from cylinder block. Install knock
sensor and connect knock sensor wire connector. Lower vehicle.
SPEED SENSOR
Removal & Installation
Disconnect speed sensor wire connector. Remove 2 speed
sensor retaining bolts at transmission housing. Install speed sensor
and connect speed sensor wire connector.
STARTER MOTOR RELAY
Removal & Installation
Disconnect negative battery cable. Identify, tag and
disconnect wiring to relay. Remove relay retaining screws and remove
relay from inner fender panel. Install replacement relay and connect
relay wires. Connect negative battery cable. Test relay operation.
MANIFOLD AIR/FUEL TEMPERATURE (MAT) SENSOR
Removal & Installation
Disconnect wire connector from MAT sensor. Remove MAT sensor
from intake manifold. To install, reverse removal procedure.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
Removal & Installation
Disconnect wire connector, vacuum hose, and retaining nuts
from MAP sensor. Remove sensor from firewall. To install, reverse
removal procedure.
FUEL INJECTOR
WARNING: Always relieve residual fuel pressure in fuel delivery
system before opening system. To prevent chance of personal
injury, cover fittings with shop towel while disconnecting
fittings.