engine JEEP CHEROKEE 1988 Service Repair Manual

COOLANT TEMPERATURE SENSOR (CTS)
Removal & Installation
Allow engine to cool down. Disconnect CTS wiring harness.
Remove CTS from intake manifold and rapidly plug hole to prevent
coolant loss. Install replacement CTS and connect CTS wiring harness.
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.
Removal
Remove air cleaner assemby. Remove injector wiring
connector. Remove injector retainer screws and clip. Using small
pliers, carefully grasp center collar of injector between electrical
terminals and carefully remove injector with lifting/twisting motion.
Discard both "O" rings. See Fig. 6.
Installation
1) Using light oil, lubricate new upper and lower "O" rings.
Install "O" rings in housing bore. Install back-up ring over upper
"O" ring. Position replacement injector in fuel body.
2) Center nozzle in lower housing bore and use a
pushing/twisting motion to seat injector. Align wire connectors in
proper orientation. Install retainer clip and screws. Connect
injector wiring. Install air cleaner.
Fig. 6: Fuel Injector & Throttle Body Assembly
Courtesy of Chrysler Motors.
FUEL PRESSURE REGULATOR

Removal & Installation
Remove throttle body assembly as previously described.
Remove Torx head retaining screws. Remove throttle position sensor
from throttle shaft lever. To install, reverse removal procedure.
Adjust TPS after installation. See ADJUSTMENTS in this article.
MANIFOLD AIR/FUEL TEMPERATURE (MAT) SENSOR
Removal & Installation
Disconnect wire harness connector from MAT sensor. Remove
MAT sensor from intake manifold. To install, reverse removal
procedure. See Fig. 7.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
Removal & Installation
Disconnect wire harness connector, vacuum hose, and
retaining nuts from MAP sensor. Remove sensor from firewall. To
install, reverse removal procedure.
ELECTRONIC CONTROL UNIT (ECU)
Removal & Installation
1) On Wrangler, remove passenger assist handle and glove box
assembly. Remove ECU bracket retaining nuts from engine compartment
side of firewall. Disconnect ECU wiring harness. Remove ECU from
bracket. To install, reverse removal procedure.
2) On all other models, remove retaining screws and bracket
that supports ECU above accelerator pedal. Remove ECU and disconnect
wiring harness. To install, reverse removal procedure.
EGR VALVE
Removal & Installation
Disconnect vacuum hose from EGR valve. Remove bolts which
hold EGR valve to intake manifold. Remove valve and discard gasket.
To install valve, reverse removal procedure. Always use new gasket.
See Fig. 7 .
TROUBLESHOOTING AND DIAGNOSIS

Fig. 23: TEST 5: BASIC ENGINE

2.5L TBI
1) Adjustment of fuel pressure is required after replacement
of pressure regulator. Remove air inlet from throttle body. Connect
tachometer to diagnostic connector terminals D1-1 and D1-3. Connect
fuel pressure gauge to fuel body pressure test fitting.
NOTE: Some TBI models do not have a pressure test fitting on
throttle body. Use Fitting (PN 8983 501 572) for this
purpose.
2) Start engine and accelerate to 2000 RPM. Turn adjustment
screw to obtain 14.5 psi (1.02 kg/cm
) fuel pressure. Location of
adjustment screw is on bottom of regulator. Install lead seal ball to
cover regulator adjustment screw after adjusting fuel pressure to
specification. Turn ignition off. Disconnect fuel pressure gauge.
Install cap on test fitting. Install air inlet.
NOTE: To increase fuel pressure, turn adjustment screw inward. To
decrease fuel pressure, turn adjustment screw outward.
4.0L MPFI
1) Remove cap from pressure test port in fuel rail. Connect
Fuel Pressure Gauge (J-37730-1) to pressure fitting. Start vehicle.
Pressure should be approximately 31 psi (2.7 kg/cm
) with vacuum
hose connected to pressure regulator.
2) Pressure should be 39 psi (2.74 kg/cm
) with vacuum
hose removed from regulator. If fuel pressure is not to
specifications, check for kinks or restricting bends in fuel supply
and return lines. Check fuel pump flow rate. Pump should deliver
minimum of 1.06 quarts (one liter) of fuel per minute with fuel
return line pinched off.
3) If flow is inadequate, check system for plugged fuel
filter or filter sock. Fuel pump flow rate can be checked by
connecting a hose to fuel test port on fuel rail and inserting other
end in clean container.
4) To operate fuel pump, install a jumper wire into
diagnostic connector terminals D1-5 and D1-6. Pinch off fuel return
line to ensure that no fuel returns to fuel tank. If fuel pressure is
still not to specifications and fuel flow is normal, replace
regulator.
REMOVAL & INSTALLATION
FUEL PUMP
Removal (2.5L TBI)
1) Disconnect battery cables. Ensure fuel level is less than
1/2 for this procedure. Remove fuel outlet and return hoses. Remove
sending unit wires. Remove sending unit retaining lock ring.
2) Remove sending unit/pump assembly with "O" ring seal.
Disconnect fuel hose from fuel pump. Disconnect wires from fuel pump.
Remove fuel pump from sending unit.
Installation
Clean seal contact are of fuel tank. Install new "O" ring
seal. Install a new filter on end of suction tube. Position sending
unit/pump assembly in tank. To complete installation, reverse removal
procedure. Start engine and check for leaks.
CAUTION: Fuel leaks can develop from over tightening sending
unit/pump during installation.

Removal (4.0L MPFI)
Install clamps (MOT. 453.01) on fuel pump inlet and outlet
hoses. Disconnect hoses from fuel pump. Disconnect electrical
connectors. Remove retaining strap. Remove fuel pump.
Installation
To install, reverse removal procedure. Ensure that clamps
(MOT. 453.01) have been removed from fuel lines. Start engine and
check for leaks.
NOTE: Accumulator is located between fuel pump and fuel filter on
4.0L models.

GEN ER AL C O OLIN G S YSTE M S ER VIC IN G

1988 J e ep C hero ke e
GENERAL INFORMATION
General Cooling System Servicing
* PLEASE READ THIS FIRST *
The following article is for general information only.
Information may not apply to all years, makes and models. See specific
article in the ENGINE COOLING section.
DESCRIPTION
The basic liquid cooling system consists of a radiator, water
pump, thermostat, electric or belt-driven cooling fan, pressure cap,
heater, and various connecting hoses and cooling passages in the block
and cylinder head.
MAINTENANCE
DRAINING
Remove radiator cap and open heater control valve to maximum
heat position. Open drain cocks or remove plugs in bottom of radiator
and engine block. In-line engines usually have one plug or drain cock,
while "V" type engines will have 2, one in each bank of cylinders.
CLEANING
A good cleaning compound removes most rust and scale. Follow
manufacturer's instructions in the use of cleaner. If considerable
rust and scale has to be removed, cooling system should be flushed.
Clean radiator air passages with compressed air.
FLUSHING
CAUTION: Some manufacturers use an aluminum and plastic radiator.
Flushing solution must be compatible with aluminum.
Back Flushing
Back flushing is an effective means of removing cooling
system rust and scale. The radiator, engine and heater core should be
flushed separately.
Radiator
To flush radiator, connect flushing gun to water outlet of
radiator and disconnect water inlet hose. To prevent flooding engine,
use a hose connected to radiator inlet. Use air in short bursts to
prevent damage to radiator. Continue flushing until water runs clear.
Engine
To flush engine, remove thermostat and replace housing.
Connect flushing gun to water outlet of engine. Flush using short air
bursts until water runs clean.
Heater Core
Flush heater core as described for radiator. Ensure heater
control valve is set to maximum heat position before flushing heater.

REFILLING
To prevent air from being trapped in engine block, engine
should be running when refilling cooling system. After system is full,
continue running engine until thermostat is open, then recheck fill
level. Do not overfill system.
TESTING
THERMOSTAT
1) Visually inspect thermostat for corrosion and proper
sealing of valve and seat. If okay, suspend thermostat and thermometer
in a 50/50 mixture of coolant and water. See Fig. 1. Do not allow
thermostat or thermometer to touch bottom of container. Heat water
until thermostat just begins to open.
2) Read temperature on thermometer. This is the initial
opening temperature and should be within specification. Continue
heating water until thermostat is fully open and note temperature.
This is the fully opened temperature. If either reading is not to
specification, replace thermostat.
Fig. 1: Testing Thermostat in Anti-Freeze/Water Solution
PRESSURE TESTING
A pressure tester is used to check both radiator cap and

complete cooling system. Test components as follows, following tool
manufacturer's instructions.
Radiator Cap
Visually inspect radiator cap, then dip cap into water and
connect to tester. Pump tester to bring pressure to upper limit of cap
specification. If cap fails to hold pressure, replace cap.
Fig. 2: Testing Radiator Pressure Cap
Cooling System
1) With engine off, wipe radiator filler neck seat clean.
Fill radiator to correct level. Attach tester to radiator and pump
until pressure is at upper level of radiator rating.
2) If pressure drops, inspect for external leaks. If no leaks
are apparent, detach tester and run engine until normal operating
temperature is reached. Reattach tester and observe. If pressure
builds up immediately, a possible leak exists from a faulty head
gasket or crack in head or block.
NOTE: Pressure may build up quickly. Release any excess pressure
or cooling system damage may result.
3) If there is no immediate pressure build up, pump tester to
within system pressure range (on radiator cap). Vibration of gauge
pointer indicates compression or combustion leak into cooling system.
Isolate leak by shorting each spark plug wire to cylinder block. Gauge
pointer should stop or decrease vibration when leaking cylinder is
shorted.

HEA TE R S YSTE M

1988 J e ep C hero ke e
1988 HEATER SYSTEMS
Jeep
DESCRIPTION
Jeep vehicles use a blend-air type heater system. Wrangler
models have a constant flow type system with engine coolant
continuously flowing through heater core. Cherokee and Comanche use
heater control valves. Coolant flow to heater core on these models can
be stopped or diverted.
On all models, temperature of heated air entering passenger
compartment is controlled by regulating amount of air flowing through
heater core and then blending it with a controlled amount of cool air
by-passing heater core.
CONTROL PANEL OPERATION
Control panel on all models includes fan switch, sliding
temperature control lever and sliding mode lever.
DEFROSTER CONTROL
Defroster control operates heater housing door regulating
heater and defroster operation by directing flow of air through
defroster hose or floor outlets. When control knob is pushed in,
blended air will enter passenger compartment through floor heat duct.
When control is pulled completely out, door directs all heated air to
windshield defroster outlets. Any intermediate position divides air
flow between windshield and floor outlets.
TEMPERATURE CONTROL LEVER (CHEROKEE, COMANCHE & WRANGLER)
Lower control lever operates blend-air door in heater core
housing. At full right position, all air is directed through heater
core, providing maximum heat flow. At full left position, all air is
directed around heater core providing fresh air. Control can be set in
any intermediate position to provide a blend of heated and unheated
air. With control lever in "COOL" position, water valve will close
(except Wrangler). Mode control lever must be in "HEAT" or defroster
mode before any air can enter vehicle.
MODE CONTROL LEVER (CHEROKEE & COMANCHE)
Mode control lever includes "BI-LEVEL", "VENT", "HEAT" and
"OFF" positions. At far end of scale, a symbol for defroster indicates
defrost position. In "BI-LEVEL" position, a mixture of floor heat and
defroster air is obtained.
FAN CONTROL
Fan control is a 4-position control switch, regulating blower
motor and air flow for heat and defrost. Switch has "LOW", "HIGH" and
2 intermediate positions. Fan will remain on unless mode lever is
placed in "OFF" position.
CONTROL CABLES ADJUSTMENT

Fig. 2: Typical Heater & Defroster Components
Courtesy of Chrysler Motors.
BLOWER MOTOR R & I
NOTE: On Cherokee and Comanche, blower motor and fan are removed
from engine compartment.
Removal & Installation
1) Remove heater core housing assembly. On all models, remove
blower motor electrical connectors. Detach screws retaining blower
motor assembly to heater housing. Remove blower motor and fan
assembly. On Cherokee and Comanche, detach fan retaining clip from fan
hub, if necessary. Remove fan from motor shaft.
2) To install, reverse removal procedure. If removed, ensure
ears of retaining clip are over flat surface on motor shaft. Check
blower motor and heater operation.
CONTROL PANEL R & I
Removal & Installation
1) Disconnect battery ground. On Cherokee, remove lower
instrument panel. On all models, remove instrument panel bezel. On
Cherokee, remove clock and radio (if equipped).
2) On all models, remove heater control panel attaching
screws. Pull out control panel and disconnect vacuum hoses, wires and
cables. Note locations for reassembly reference. Remove control panel.
To install, reverse removal procedure.
CONTROL CABLES R & I
REMOVAL (CHEROKEE & COMANCHE)
Remove control panel. Detach cable from heater control panel.