1988 JEEP CHEROKEE engine

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.

Remove retaining clip and cable self-adjusting clip from blend-air
door lever at bottom of blower housing. Remove cable by squeezing tabs
with needle nose pliers. Do not break housing.
INSTALLATION
To install, connect cable self-adjusting clip to blend-air
door lever, then snap cable into position. Install retaining clip onto
blend-air door lever. Route cable to A/C-heater control panel and
connect. Install control panel.
REMOVAL & INSTALLATION (WRANGLER)
1) Disconnect cables from vent doors. Disconnect cables from
heater control panel levers. Remove cables by squeezing tabs with
needle nose pliers.
2) Connect and adjust cables as described in ADJUSTMENTS
section of this article
HEATER CORE R & I
REMOVAL & INSTALLATION (CHEROKEE & COMANCHE)
1) Disconnect battery ground. Drain cooling system.
Disconnect heater hoses at heater core inlet and outlet tubes.
Disconnect blower motor wires and vent tube. Remove console (if
equipped). Remove lower instrument panel.
2) Disconnect electrical connectors from blower motor
resistors. Disconnect vacuum hose at vacuum motor. Cut plastic
retaining strap holding blower housing to heater core housing.
3) Disconnect and remove heater control cable. Detach clip at
rear of blower housing flange and remove retaining screws. Remove
housing mounting nuts from studs on engine compartment side of dash
panel. Remove right kick panel.
4) Remove instrument panel support bolt. Gently pull on right
side of dash, then rotate housing downward and toward rear of vehicle
to disengage housing studs from dash panel. Remove blower housing.
Detach retaining screws and remove heater core by pulling it straight
out of housing.
5) To install, reverse removal procedure. Ensure seal is
cemented in place to prevent movement when blower assembly is
installed. Connect heater hoses and fill cooling system.
REMOVAL & INSTALLATION (WRANGLER)
1) Disconnect battery ground. Drain about 2 quarts of coolant
from radiator. Disconnect heater hoses at heater core inlet and outlet
tubes. Disconnect vent door cables. Disconnect blower motor wires.
Disconnect defroster duct.
2) Remove nuts attaching heater housing studs to engine
compartment side of dash panel. Remove heater housing assembly by
tilting it downward, to disengage it from defroster duct.
3) Pull heater housing rearward and out from under instrument
panel. Remove heater housing cover from heater housing assembly.
Remove heater core from housing.
HEATER SYSTEM OPREATION CHART & VACUUM DIAGRAM
HEATER SYSTEM OPERATION TABLE







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IG NIT IO N S YSTE M - 2 .5 L W /R EN IX E LE C TR O NIC IG NIT IO N

1988 J e ep C hero ke e
Distributors & Ignition Systems
JEEP RENIX ELECTRONIC IGNITION
2.5L TBI: Cherokee, Comanche, Wagoneer, Wrangler
DESCRIPTION
The Renix electronic ignition system consists of a solid-
state Ignition Control Module (ICM), a distributor, a Top Dead Center
(TDC) sensor, and an Electronic Control Unit (ECU).
OPERATION
IGNITION CONTROL MODULE (ICM)
The ignition control module is located in engine compartment,
just left of battery. The ICM consists of a solid-state ignition
circuit and an integrated ignition coil that can be removed and
serviced separately.
Electronic signals from the electronic control unit to the
ICM determine the amount of ignition timing or retard needed to meet
various engine requirements. The electronic control unit provides an
input signal to the ICM. The ICM has only 2 outputs: a tach signal to
the tachometer and diagnostic connector, and a high voltage signal
from the coil to the distributor cap.
TDC SENSOR
The TDC sensor senses TDC and BDC crankshaft positions as
well as engine RPM. Sensor is located on left rear side of engine and
is not adjustable. Sensor is secured by special shouldered bolts to
flywheel/drive plate housing.
TESTING
1) Disconnect ignition coil wire from center tower of
distributor cap. Using insulated pliers, hold coil wire about 1/2" (13
mm) away from engine block. Crank engine and check for spark between
wire and engine block.
2) If spark occurs, reconnect coil wire to distributor cap.
Remove spark plug wire from one spark plug. Using insulated pliers,
hold wire about 1/2" (13 mm) away from engine block.
3) Crank engine and check for spark between wire and engine
block. If spark occurs, check fuel system for problems. If no spark
occurs, check for a defective rotor, distributor cap, or spark plug
wires. Replace parts as necessary.
4) If rotor, cap and wires are okay, check for loose or
corroded connections at coil terminals. If necessary, clean terminals
and wires. Ensure wires are properly seated on coil terminals and not
wedged between coil body and terminal. If okay, go to next step.
5) Check for loose connectors at ICM or ECU. Verify that wire
connectors are firmly plugged into ICM and ECU. Also check for loose
ICM or ECU ground wire connections at oil dipstick bracket. Clean and
tighten if necessary.
6) Load test battery to ensure battery is fully charged.
Replace battery if necessary. If battery is okay, check voltage
between terminals "A" and "B" of ICM connector while cranking engine.
See Fig. 1 .