JEEP CHEROKEE 1988 Service Repair Manual

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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MODE       

 LEVER   BLOWER  PANEL  FLOOR  DEFROST  WATER 


POSITION AIR DISCHARGE SPEEDS  DOOR  DOOR  DOOR  VALVE 










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Off  Closed  None  Closed Closed Closed  Closed 










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Vent  Panel  4  Open  Closed Closed  Closed 

 Registers      










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Bi-Level  Panel  4  Open  Open  Bleed  Open
(1)

 Registers      

 and Floor      

 With Def.      

 Bleed      










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Heat  Floor With  4  Closed Open  Bleed  Open
(1)

 Def. Bleed      










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Def.  Defroster  4  Closed Closed Open  Open
(1)

      










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(1)
- Water valve closes in full "COOL" temperature lever position. 










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Fig. 3: Heater Control System Vacuum Diagram

WIRING DIAGRAMS

Fig. 4: Heater Wiring Diagram (Comanche Diesel)

Fig. 5: Heater Wiring Diagram (Comanche Gas)
Fig. 6: Heater Wiring Diagram (Wrangler)

IG NIT IO N S W IT C H & L O CK C YLIN DER

1988 J e ep C hero ke e
1988 Ignition Switch & Lock Cylinders
JEEP
DESCRIPTION
The ignition switch and lock cylinder is typically mounted on
the steering column and actuated by an ignition key.
SERVICING
To gain access to ignition components on Jeep vehicles, the
steering column must be removed or lowered and the turn signal switch
must be removed.
CAUTION: The lock plate is held by high spring pressure. DO NOT
remove snap ring without using a compressor tool. If the
steering shaft has standard threads, use Compressor Tool
(J-23653); if the shaft has metric threads use Metric
Forcing Screw (J-23653-4).
CAUTION: Special care must be taken to avoid bumping, jolting or
hammering on the steering shaft and gearshift tube.
REMOVAL & INSTALLATION
LOCK CYLINDER
Removal
Turn lock cylinder clockwise 2 detent positions beyond
"OFF-LOCK" position. Compress lock cylinder retaining tab using a thin
bladed screwdriver and remove lock cylinder.
Fig. 1: Typical Column Type Ignition Switch Lock Cylinder Removal
On most vehicles, push in to release lock retainer.
Installation
Insert key in lock. Hold cylinder sleeve, and turn key

clockwise until key stops. Insert cylinder lock into bore with
cylinder tab aligned with keyway in housing. Push cylinder in until it
bottoms. Rotate cylinder counterclockwise to engage lock sector, and
push in until cylinder tab engages in housing groove.
IGNITION SWITCH
Removal
Lower column and remove switch mounting screws. Disconnect
harness connector. Remove switch.
Installation
Move switch slider to "ACC" position. Move switch slider back
2 clicks to "OFF-UNLOCK" position. Insert remote rod in switch slider,
and position switch on column. Do not move slider. Install and tighten
screws.
Fig. 2: Rod-Actuated Ignition Switch

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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 .

7) Minimum voltage reading should be 9.5 volts. If voltage is
okay, go to next step. If voltage is low, check continuity of ICM and
ECU ground wires. Repair or replace as necessary.
8) Using an ohmmeter, check ignition coil resistance.
Resistance on primary winding should be .4-.8 ohms. Secondary
resistance should be 2500-4000 ohms. If correct, go to next step. If
not, replace ignition coil.
9) Check ECU and ICM with Tester (MS 1700). Replace ICM or
ECU if either fails MS 1700 test sequence.
Fig. 1: 2.5L TBI ICM Connector Terminals
Courtesy of American Motors/Jeep Corp.
OVERHAUL
NOTE: The 2.5L TBI distributor contains no electrical components
other than the rotor and distributor cap. If any other
distributor part is defective, the entire distributor
assembly must be replaced.

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IG NIT IO N S YSTE M - 4 .0 L W /S O LID S TA TE IG NIT IO N ( S SI)
1 988 J e ep C hero ke e
DISTRIBUTORS & IGNITION SYSTEMS
Jeep Solid State Ignition
4.0L 6-Cylinder
DESCRIPTION
IGNITION SYSTEM GENERAL DESCRIPTION
The Solid State Ignition (SSI) system features a solid state
Ignition Control Module (ICM)/ignition coil assembly, Electronic
Control Unit (ECU), distributor and engine speed sensor. Other
components include the battery, ignition switch, starter solenoid,
spark plugs and wires, cap and rotor, resistance wire, by-pass wire
and a knock sensor. A sync pulse signal generator (stator) inputs the
firing order to the ECU.
Fig. 1: 4.0L 6-Cylinder Firing Order
IGNITION CONTROL MODULE (ICM)
The ignition control module is mounted to the ignition coil.
See Fig. 2 . Based on control system inputs, the ECU triggers the
ignition coil via the ignition control module. The ECU is able to
advance or retard ignition timing by controlling the ignition coil
through the ignition control module.
The ICM consists of a solid state ignition circuit, an
integrated ignition circuit and an integrated ignition coil that can
be removed and serviced separately if necessary.

The ECU provides an input signal to the ICM. The ICM has only
two outputs:
* Tach signal to the tachometer and diagnostic connector
* High voltage from the coil to the distributor cap
Fig. 2: View of Ignition Control Module/Ignition Coil Assembly
IGNITION CONTROL MODULE (ICM) ELECTRICAL FEED CONNECTIONS
Electrical feed to the ICM is through terminal "A" of
Connector No. 1 on the module. See Fig. 3.
NOTE: Electrical supply only occurs with the ignition switch in
the START and RUN position.