1994 JEEP CHEROKEE ECU

ENGINE BLOCK HEATER
GENERAL INFORMATION
DESCRIPTION AND OPERATION
An optional engine block heater is available for all
models. The heater is equipped with a power cord.
The cord is attached to an engine compartment com-
ponent with tie-straps. The heater warms the engine
providing easier engine starting and faster warm-up
in low temperatures. The heater is mounted in a core
hole of the engine cylinder block (in place of a freeze
plug) with the heating element immersed in engine
coolant. Connect the power cord to a grounded 110-
120 volt AC electrical outlet with a grounded, three-
wire extension cord.
WARNING: DO NOT OPERATE ENGINE UNLESS
BLOCK HEATER CORD HAS BEEN DISCONNECTED
FROM POWER SOURCE AND SECURED IN PLACE.
BLOCK HEATER SPECIFICATIONS
²2.5L Engine: 115 Volts 400 Watts
²4.0L Engine: 120 Volts 600 Watts
REMOVAL
Refer to correct illustration (Figures 11, 12 or 13)
when servicing block heater.
WARNING: DO NOT REMOVE THE CYLINDER
BLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR
DRAINCOCK WITH THE SYSTEM HOT AND PRES-
SURIZED. SERIOUS BURNS FROM THE COOLANT
CAN OCCUR.
DO NOT WASTE reusable coolant. If solution is
clean, drain coolant into a clean container for reuse.
(1) Drain coolant from radiator and engine cylin-
der block.
(2) Unplug power cord from block heater.
(3) Loosen screw in center of block heater (Figs.
11, 12 or 13).
(4) Remove block heater from cylinder block.
INSTALLATION
(1) Thoroughly clean the engine core hole and the
block heater seat.
(2) Insert block heater assembly into core hole
with element loop pointingUp.
(3) Seat block heater flush against block face.
Tighten mounting screw to 3.6 Nzm (32 in. lbs.)
torque.
(4) Fill cooling system with coolant. Pressurize sys-
tem and inspect for leaks.
(5) Plug power cord into block heater. Route cord
away from moving parts, linkages and exhaust sys-
tem components. Secure cord in place with tie-straps.
Fig. 11 Heater and CordÐXJ with 2.5L Engine
Fig. 12 Heater and CordÐXJ with 4.0L Engine
Fig. 13 Heater and CordÐYJ Models
JCOOLING SYSTEM 7 - 37

SPECIFICATIONS
IGNITION OFF DRAW (IOD) DIAGNOSIS
GENERAL INFORMATION
Ignition off draw refers to power being drained
from the battery with the ignition switch turned off.
A normal vehicle electrical system will draw from 5
to 20 milliamps. This is with the ignition switch in
the OFF position, and all non-ignition controlled cir-
cuits in proper working order. A vehicle that has not
been operated for approximately 20 days, may dis-
charge the battery to an inadequate level. Battery
drain should not exceed approximately 20 MA (20
milliamps = 0.020 amps).
The 20 MA are needed to supply PCM memory,
digital clock memory, and ETR (electronically tuned
radio) memory.
Excessive battery drain is caused by items left
turned on, internally shorted generator, or intermit-
tent short in wiring.
If the IOD is over 20 milliamperes, the defect must
be found and corrected before replacing a battery. In
most cases the battery can be charged and returned
to service.
When a vehicle will not be used for 20 days or
more (stored), remove IOD fuse in the Power Distri-
bution Center to reduce battery discharging.
TEST PROCEDURE
Testing for higher amperage IOD must be per-
formed first to prevent damage to most milliamp
meters.
(1) Verify that all electrical accessories are OFF.
Turn off all lamps, remove ignition key, and close all
doors. If the vehicle is equipped with electronic acces-
sories (illuminated entry, high line radio), allow the
systems to automatically shut off (time out), up to 3
minutes.
(2) Determine that the underhood lamp is operat-
ing properly, then disconnect or remove bulb.
(3) Disconnect negative cable from battery.
(4) Connect a typical 12-volt test lamp (low watt-
age bulb) between the negative cable clamp and the
battery negative terminal. If equipped with security
alarm, cycle the key in the door to turn off the flash-ing lights. Make sure that the doors remain closed so
that illuminated entry is not activated.
The test lamp may light brightly for up to 3 min-
utes or may not light at all (depending on the elec-
trical equipment). The term brightly being used
throughout the following tests, implies the bright-
ness of the test lamp will be the same as if it were
connected across the battery.
The test lamp must be securely clamped to the neg-
ative cable and battery terminal. If the test lamp be-
comes disconnected during any part of the IOD test,
the electronic timer function will be activated and all
tests must be repeated.
If the ammeter circuit is broken the Security
Alarm Module will turn on parking lamps.
(5) After 3 minutes, the test lamp should turn OFF
or be DIMLY lit (depending on the electrical equip-
ment). If the test lamp remains brightly lit do not
disconnect it. Remove each fuse or circuit breaker
(refer to Group 8 - Wiring Diagrams) until test lamp
is either OFF or DIMLY lit. This will eliminate the
higher amperage draw.
If test lamp is still bright after disconnecting each
fuse and circuit breaker, disconnect the wiring har-
ness from the generator. Refer to Generator Test Pro-
cedures in this group. Do not disconnect the test
lamp.
After higher amperage IOD has been corrected, low
amperage IOD may be checked.
It is now safe to install milliamp meter to check for
low amperage IOD.
(6) With test lamp still connected securely, clamp
an ammeter between battery negative terminal and
negative battery cable.
Do not open any doors or turn on any electri-
cal accessories with the test lamp disconnected
or the meter may be damaged.
(7) Disconnect test lamp. The current draw should
not exceed 0.020 amp. If it exceeds 0.020 milliamps,
isolate each circuit by removing circuit breakers and
fuses. The meter reading drops once the high current
problem is found. Repair this section of the circuit,
whether it is a wiring short or component failure.
BATTERY CLASSIFICATIONS AND RATINGSTORQUE SPECIFICATIONS
8A - 8 BATTERY/STARTING/CHARGING SYSTEMS DIAGNOSTICSJ

(4) Ensure that tang at battery base is positioned
in tray properly before tightening holddown.
CAUTION: It is imperative that the cables are con-
nected to the battery positive-to-positive and nega-
tive-to-negative. Reverse polarity will damage the
generator diodes and radio(s).
(5) Place felt washer on positive battery terminal.
(6) Connect positive cable first. Then connect neg-
ative cable. Tighten both cable terminal bolts to 8.5
Nzm (75 in. lbs.).(7) Apply a thin coating of petroleum jelly or chas-
sis grease to cable terminals and battery posts.
(8) Inspect negative cable connections on engine
and vehicle body for condition, security and electrical
continuity.
BATTERY REPLACEMENTÐRIGHT HAND DRIVE
REMOVAL
(1) Make sure ignition switch is in OFF position
and all electrical accessories are OFF.
Fig. 2 Battery HolddownÐXJ
Fig. 3 Battery HolddownÐYJ
Fig. 4 Battery TrayÐXJ
Fig. 5 Battery TrayÐYJ
8B - 2 BATTERY/STARTER/GENERATOR SERVICEJ

(2) Remove bolt and negative cable from battery
(Fig. 6).
(3) Remove bolt and positive cable from battery.
WARNING: WEAR A SUITABLE PAIR OF RUBBER
GLOVES (NOT THE HOUSEHOLD TYPE) WHEN RE-
MOVING A BATTERY BY HAND. SAFETY GLASSES
ALSO SHOULD BE WORN. IF THE BATTERY ISCRACKED OR LEAKING, THE ELECTROLYTE CAN
BURN THE SKIN AND EYES.
(4) Remove battery holddown and battery from ve-
hicle.
(5) Inspect battery tray and holddowns for corro-
sion. Remove corrosion using a wire brush and a so-
dium bicarbonate/water solution. Paint any exposed
bare metal. Replace damaged components.
INSTALLATION
(1) Refer to Specifications to determine if battery
has correct classification and rating for the vehicle.
(2) Use a hydrometer to test the battery electro-
lyte. Charge battery if necessary.
(3) Position battery in tray. Ensure that positive
and negative terminals are correctly located. The ca-
bles must reach their terminals without stretching
(Fig. 6).
(4) Ensure that battery base is positioned in tray
properly before tightening holddown.
CAUTION: It is imperative that the cables are con-
nected to the battery positive-to-positive and nega-
tive-to-negative. Reverse polarity will damage the
generator diodes and radio(s).
(5) Connect positive cable first. Then connect neg-
ative cable. Tighten both cable terminal bolts to
10-20 Nzm (90-178 in. lbs.).
(6) Inspect negative cable connections on engine
and vehicle body for condition, security and electrical
continuity.
Fig. 6 Battery Cable Attachment
JBATTERY/STARTER/GENERATOR SERVICE 8B - 3

CAUTION: Do not puncture the spark plug cables or
boots to make the connection. Use proper adapters.
(6) Connect battery cable to battery.
ENGINE ROTATED AFTER REMOVAL
There is a fork on the distributor housing where
the housing seats against the engine block. The slot
in the fork aligns with the hole for the distributor
holddown bolt in the engine block. The distributor is
correctly installed when the rotor is correctly posi-
tioned. This is when the slot in the fork is aligned
with the hole for the distributor holddown bolt in the
cylinder block. Because of the fork on the distributor
housing, initial ignition timing is not adjustable (the
distributor cannot be rotated).
(1) If the engine was rotated while the distributor
was removed, it will be necessary to establish timing
according to following procedure:
²Remove the No. 1 spark plug. Hold a finger over
the spark plug hole and rotate the engine until com-
pression pressure is felt. Slowly continue to rotate
the engine. Do this until the timing index on vibra-
tion damper pulley aligns with top dead center (TDC)mark (0 degree) on timing degree scale. Always ro-
tate the engine in direction of normal rotation. Do
not turn the engine backward to align the timing
marks.
²Using a flat blade screwdriver, rotate the oil pump
gear. Do this to position the gear slot on the oil
pump shaft slightly before the 11 o'clock position
(Fig. 11).
²With the distributor cap removed, install the dis-
tributor with the rotor located just past the 2 o'clock
position (Fig. 12).
²When distributor is fully engaged in its correct lo-
cation, the rotor should be just past the 3 o'clock po-
sition (Fig. 13).
²Install the distributor holddown clamp and bolt.
Tighten the holddown bolt to 23 Nzm (17 ft. lbs.)
torque.
CAUTION: If the distributor cap is incorrectly posi-
tioned on distributor housing, the cap or rotor may
be damaged when engine is started.
(2) Install the distributor cap (with ignition cables)
on the distributor housing. Be sure that the cap fits
securely on rim of the distributor housing.
(3) Connect the distributor wiring harness to the
main engine harness.
CAUTION: Do not puncture the spark plug cables or
boots to make the connection. Use proper adapters.
REMOVALÐ4.0L ENGINE
The distributor used in the 4.0L engine contains an
internal oil seal that prevents oil from entering the
distributor housing. The seal is not serviceable.
Fig. 11 Align Oil Pump Gear SlotÐ2.5L Engine
Fig. 10 Spark Plug Cable PositionsÐ2.5L Engine
Fig. 12 Distributor InstallationÐ2.5L Engine
8D - 24 IGNITION SYSTEMSJ

INSTALLATION
(1) Install MAP sensor to dash panel and secure
with mounting nuts.
(2) Install the MAP sensor vacuum supply hose.
(3) Connect the MAP sensor electrical connector.
OXYGEN (O2S) SENSOR
For diagnostics and removal/installation proce-
dures, refer to Group 14, Fuel Systems, in this man-
ual.
POWERTRAIN CONTROL MODULE (PCM)
The PCM was formerly referred to as the SBEC or
engine controller.
XJ MODELS
On XJ models, the PCM is located in the engine
compartment next to the air cleaner (Fig. 24).
REMOVAL
(1) Disconnect negative battery cable at battery.
(2) Loosen 60-way connector mounting screw until
connector can be disengaged from PCM.
(3) Pull 60-way connector straight back from PCM.
(4) Remove PCM mounting bolts.
(5) Remove PCM from vehicle.
INSTALLATION
(1) Check the pins in the PCM 60-way electrical
connector for damage. Repair as necessary.
(2) Install PCM. Tighten mounting bolts to 1 Nzm
(9 in. lbs.) torque.
(3) Engage 60-way connector into PCM. Tighten
connector mounting screw to 4 Nzm (35 in. lbs.)
torque.
(4) Connect battery cable to battery.
YJ MODELS
On YJ models, the PCM is located in the engine
compartment behind the windshield washer fluid res-
ervoir (Fig. 25).REMOVAL
(1) Disconnect negative battery cable at battery.
(2) Remove windshield washer fluid reservoir.
(3) Loosen 60-way connector mounting screw until
connector can be disengaged from PCM.
(4) Pull 60-way connector straight back from PCM.
(5) Remove PCM mounting bolts.
(6) Remove PCM from vehicle.
INSTALLATION
(1) Check the pins in the PCM 60-way electrical
connector for damage. Repair as necessary.
(2) Install PCM. Tighten mounting bolts to 1 Nzm
(9 in. lbs.) torque.
(3) Engage 60-way connector into PCM. Tighten con-
nector mounting screw to 4 Nzm (35 in. lbs.) torque.
(4) Connect battery cable to battery.
(5) Install washer fluid reservoir.
SPARK PLUGS
PLUG REMOVAL
(1) Always remove spark plug or ignition coil ca-
bles by grasping at the cable boot. Turn the cable
boot 1/2 turn and pull straight back in a steady mo-
tion. Never pull directly on the cable. Internal dam-
age to cable will result.
(2) Prior to removing the spark plug, spray com-
pressed air around the spark plug hole and the area
around the spark plug. This will help prevent foreign
material from entering the combustion chamber.
(3) Remove the spark plug using a quality socket
with a rubber or foam insert.
(4) Inspect the spark plug condition. Refer to
Spark Plugs in the Diagnostics/Service Procedures
section of this group.
PLUG CLEANING
The plugs may be cleaned using commercially
available spark plug cleaning equipment. After
Fig. 24 PCM LocationÐXJ Models
Fig. 25 PCM LocationÐYJ Models
8D - 28 IGNITION SYSTEMSJ

cleaning, file the center electrode flat with a small
point file or jewelers file before adjusting gap.
PLUG GAP ADJUSTMENT
Check the spark plug gap with a gap gauge tool. If
the gap is not correct, adjust it by bending the
ground electrode (Fig. 26).Never attempt to adjust
the gap by bending the center electrode.
SPARK PLUG GAP
²2.5L Engine Spark Plug Gap: .89 mm (.035 in).
²4.0L Engine Spark Plug Gap: .89 mm (.035 in).
PLUG INSTALLATION
Always tighten spark plugs to the specified torque.
Over tightening can cause distortion. This may re-
sult in a change in the spark plug gap.
When replacing the spark plug and ignition coil ca-
bles, route the cables correctly and secure them in
the appropriate retainers. Failure to route the cables
properly can cause the radio to reproduce ignition
noise. It could cause cross ignition of the spark plugs,
or short circuit the cables to ground.
(1) Start the spark plug into the cylinder head by
hand to avoid cross threading.
(2) Tighten the spark plugs to 35-41 Nzm (26-30 ft.
lbs.) torque.
(3) Install spark plug cables over spark plugs.
SPARK PLUG SECONDARY CABLES
CAUTION: When disconnecting a high voltage cable
from a spark plug or from the distributor cap, twistthe rubber boot slightly (1/2 turn) to break it loose.
Grasp the boot (not the cable) and pull it off with a
steady, even force.
Install cables into the proper engine cylinder firing
order (Figs. 27 or 28).
When replacing the spark plug and coil cables,
route the cables correctly and secure in the proper
retainers. Failure to route the cables properly can
cause the radio to reproduce ignition noise. It could
also cause cross ignition of the plugs, or short circuit
the cables to ground.
When installing new cables, make sure a positive
connection is made. A snap should be felt when a
good connection is made between the plug cable and
the distributor cap tower.
THROTTLE POSITION SENSOR (TPS)
For diagnostics and removal/installation proce-
dures, refer to Group 14, Fuel Systems, in this man-
ual.
Fig. 26 Setting Spark Plug GapÐTypical
Fig. 27 Engine Firing OrderÐ2.5L Engine
Fig. 28 Engine Firing OrderÐ4.0L Engine
JIGNITION SYSTEMS 8D - 29

taching screws. Do not allow the ignition switch to
move from the ACCESSORY detent position.
Because the ignition switch and the headlamp dim-
mer switch share the same two mounting screws, one
of the screws must be removed from the ignition
switch. This must be doneafterthe ignition switch
has been adjusted andbeforethe dimmer switch has
been installed. Remove one screw.Do notremove
the stud/nut.
(7) Install the headlamp dimmer switch as follows:
Slip switch into actuator rod and position over the ig-
nition switch. Install screws finger tight. Remove the
dimmer switch actuator rod securing-tape from steer-
ing column.
(8) Adjust dimmer switch as follows: Depress the
switch slightly and insert a 3/32-inch drill bit into
the adjustment hole (Fig. 1). This is done to prevent
horizontal switch movement.
(9) Move switch toward steering wheel to remove
any lash from switch actuator rod. Tighten dimmer
and ignition switch fasteners to 4 Nzm (35 in. lbs.)
torque.
(10) XJ models: Install the lower instrument panel
trim assembly. YJ models: Install the windshield
wiper intermittent control module and its bracket (if
equipped).
(11) Install the negative battery cable.
Test dimmer switch. Test ignition switch operation
in all switch positions. If equipped with a tilt steer-
ing column, test operation of dimmer switch and ig-
nition switch in all tilt positions.
Fig. 4 Detent PositionsÐNon-Tilt Steering Column
Fig. 5 Detent PositionsÐTilt Steering Column
8D - 32 IGNITION SYSTEMSJ