2002 JEEP GRAND CHEROKEE Ignition coil

8W-30 FUEL/IGNITION SYSTEM
Component Page
A/C Compressor Clutch Relay . . . 8W-30-23, 35, 39, 41, 42
A/C Pressure Transducer........ 8W-30-21, 42, 45, 31
Accelerator Pedal Position Sensor........ 8W-30-37, 48
Adjustable Pedals Module................ 8W-30-33
Adjustable Pedals Motor/Sensor Assembly.... 8W-30-33
Adjustable Pedals Switch................ 8W-30-33
Auto Shut Down Relay...... 8W-30-8, 9, 12, 24, 25, 26,
27, 28, 29, 30, 35, 39, 41
Battery Temperature Sensor.......... 8W-30-2, 11, 50
Body Control Module................... 8W-30-46
Boost Pressure Sensor.................. 8W-30-45
Brake Lamp Switch.............. 8W-30-4, 5, 32, 51
Camshaft Position Sensor........ 8W-30-18, 19, 20, 49
Capacitor........................... 8W-30-12
Capacitor No. 1....................... 8W-30-16
Capacitor No. 2....................... 8W-30-17
Clockspring...................... 8W-30-4, 5, 38
Coil On Plug No. 1.................... 8W-30-17
Coil On Plug No. 2.................... 8W-30-16
Coil On Plug No. 3.................... 8W-30-17
Coil On Plug No. 4.................... 8W-30-16
Coil On Plug No. 5.................... 8W-30-17
Coil On Plug No. 6.................... 8W-30-16
Coil On Plug No. 7.................... 8W-30-17
Coil On Plug No. 8.................... 8W-30-16
Coil Rail............................ 8W-30-12
Controller Antilock Brake........... 8W-30-2, 36, 51
Crankcase Heater..................... 8W-30-35
Crankshaft Position Sensor....... 8W-30-18, 19, 20, 49
Data Link Connector............... 8W-30-6, 7, 46
Diagnostic Junction Port.......... 8W-30-6, 7, 33, 46
EGR Solenoid........................ 8W-30-50
Electronic Speed Control Servo........... 8W-30-4, 5
Engine Control Module.... 8W-30-34, 35, 36, 37, 38, 39,
40, 41, 42, 43, 44, 45,
46, 47, 48, 49, 50, 51
Engine Coolant Temperature Sensor . . . 8W-30-21, 22, 47
Engine Oil Pressure Sensor......... 8W-30-21, 22, 45
Engine Starter Motor Relay......... 8W-30-18, 19, 39
EVAP/Purge Solenoid.................. 8W-30-4, 5
Fuel Injector No. 1............... 8W-30-13, 15, 44
Fuel Injector No. 2............... 8W-30-13, 14, 44
Fuel Injector No. 3............... 8W-30-13, 15, 44
Fuel Injector No. 4............... 8W-30-13, 14, 44
Fuel Injector No. 5............... 8W-30-13, 15, 44
Fuel Injector No. 6.................. 8W-30-13, 14
Fuel Injector No. 7..................... 8W-30-15
Fuel Injector No. 8..................... 8W-30-14
Fuel Pressure Sensor................... 8W-30-37
Fuel Pressure Solenoid.................. 8W-30-47
Fuel Pump Module.................... 8W-30-10
Fuel Pump Relay.................. 8W-30-8, 9, 10
Fuel Tank Module..................... 8W-30-45
Fuse 6........................... 8W-30-8, 42
Fuse 10............................ 8W-30-33
Fuse 11............................ 8W-30-43
Fuse 12......................... 8W-30-8, 9, 40
Fuse 13............................ 8W-30-41
Fuse 16 . . 8W-30-24, 25, 26, 27, 28, 29, 30, 35, 37, 39, 41
Component Page
Fuse 19............................. 8W-30-9
Fuse 21......................... 8W-30-4, 5, 32
Fuse 22............................ 8W-30-34
Fuse 23............................ 8W-30-39
Fuse 24............................. 8W-30-9
Fuse 26..................... 8W-30-8, 12, 41, 47
Fuse 31............................ 8W-30-39
G103....................... 8W-30-8, 34, 39, 46
G104......................... 8W-30-26, 27, 30
G105........................... 8W-30-35, 39
G108........................... 8W-30-23, 43
G123.............................. 8W-30-50
G300............................ 8W-30-4, 33
G301............................ 8W-30-5, 10
Generator...................... 8W-30-3, 23, 35
Glow Plug No. 1...................... 8W-30-42
Glow Plug No. 2...................... 8W-30-43
Glow Plug No. 3...................... 8W-30-42
Glow Plug No. 4...................... 8W-30-43
Glow Plug No. 5...................... 8W-30-42
Glow Plug Relay No. 1............. 8W-30-35, 42, 43
Glow Plug Relay No. 2............. 8W-30-35, 42, 43
Hydraulic Cooling Module . . . 8W-30-3, 24, 25, 30, 31, 43
Idle Air Control Motor.................. 8W-30-20
Intake Air Temperature Sensor....... 8W-30-21, 22, 38
Intake Port Swirl Actuator............... 8W-30-39
Junction Block......... 8W-30-4, 5, 8, 9, 32, 33, 39, 40
Knock Sensor........................ 8W-30-11
Leak Detection Pump................... 8W-30-23
Manifold Absolute Pressure Sensor.... 8W-30-20, 21, 22
Mass Air Flow Sensor.................. 8W-30-37
Output Speed Sensor.................... 8W-30-2
Oxygen Sensor 1/1 Upstream...... 8W-30-25, 26, 28, 29
Oxygen Sensor 1/2 Downstream.... 8W-30-24, 25, 26, 30
Oxygen Sensor 2/1 Upstream........ 8W-30-27, 28, 29
Oxygen Sensor 2/2 Downstream...... 8W-30-24, 27, 30
Oxygen Sensor Downstream Relay . . 8W-30-24, 26, 27, 30
Park/Neutral Position Switch............. 8W-30-33
Power Distribution Center...... 8W-30-8, 9, 12, 24, 25,
26, 27, 28, 29, 30, 34, 35,
37, 39, 41, 42, 43, 47
Powertrain Control Module . . . 8W-30-2, 3, 4, 5, 6, 7, 8, 9,
10, 11, 12, 13, 14, 15, 16, 17,
18, 19, 20, 21, 22, 23, 24, 25,
26, 27, 28, 29, 30, 31, 32
Shifter Assembly............... 8W-30-2, 32, 38, 40
Speed Control Switch No. 1........... 8W-30-4, 5, 38
Speed Control Switch No. 2........... 8W-30-4, 5, 38
Throttle Position Sensor................. 8W-30-20
Transfer Case Position Sensor........... 8W-30-8, 51
Transmission Control
Module............. 8W-30-6, 7, 20, 23, 32, 36, 40
Transmission Control Relay.............. 8W-30-23
Transmission Solenoid................ 8W-30-3, 21
Transmission Solenoid/TRS Assembly....... 8W-30-33
Viscous/Cabin Heater................... 8W-30-39
Viscous/Cabin Heater Relay...... 8W-30-35, 39, 41, 42
Wastegate Solenoid.................... 8W-30-35
Water In Fuel Sensor................... 8W-30-50
WJ8W-30 FUEL/IGNITION SYSTEM 8W - 30 - 1

COIL ON PLUG NO. 7 (4.7L) - BLACK 3 WAY
CAV CIRCUIT FUNCTION
1 K97 14BR COIL DRIVER NO. 7
2 A142 14DG/OR AUTO SHUT DOWN RELAY OUTPUT
3- -
COIL ON PLUG NO. 8 (4.7L) - BLACK 3 WAY
CAV CIRCUIT FUNCTION
1 K98 14LB/RD COIL DRIVER NO. 8
2 A142 14DG/OR AUTO SHUT DOWN RELAY OUTPUT
3- -
COIL RAIL (4.0L) - BLACK 4 WAY
CAV CIRCUIT FUNCTION
1 K91 14TN/RD COIL DRIVER NO. 1
2 A142 14DG/OR AUTO SHUT DOWN RELAY OUTPUT
3 K92 14TN/PK COIL DRIVER NO. 2
4 K93 14TN/OR COIL DRIVER NO. 3
COMPACT DISC CHANGER (PREMIUM RADIO) - BLACK 8 WAY
CAV CIRCUIT FUNCTION
1 X40 20WT/RD AUDIO OUT RIGHT
2 C235 20WT/LB SHIELD
3 D25 20YL/VT PCI BUS
4 X112 20RD IGNITION SWITCH OUTPUT (RUN-ACC)
5 X41 20WT/DG AUDIO OUT LEFT
6 Z4 20WT/BK GROUND
7 Z17 20BK GROUND
8 X160 20YL B(+)
WJ8W-80 CONNECTOR PIN-OUT 8W - 80 - 63

POWER CONNECTOR - WHITE 2 WAY
CAV CIRCUIT FUNCTION
1 F85 16VT/WT FUSED B(+)
2 Z234 16BK GROUND
POWERTRAIN CONTROL MODULE C1 (GAS) - BLACK 32 WAY
CAV CIRCUIT FUNCTION
1 K93 14TN/OR COIL DRIVER NO. 3
2 F991 18OR/DB FUSED IGNITION SWITCH OUTPUT (RUN-START)
3 K94 14TN/LG (4.7L) COIL DRIVER NO. 4
4 K4 18BK/LB SENSOR GROUND
5 K96 14TN/LB (4.7L) COIL DRIVER NO. 6
6 T41 18BK/WT PARK/NEUTRAL POSITION SWITCH SENSE (T41)
7 K91 14TN/RD COIL DRIVER NO. 1
8 K24 18GY/BK CRANKSHAFT POSITION SENSOR SIGNAL
9 K98 14LB/RD (4.7L) COIL DRIVER NO. 8
10 K60 18YL/BK IDLE AIR CONTROL NO. 2 DRIVER
11 K40 18BR/WT IDLE AIR CONTROL NO. 3 DRIVER
12 - -
13 - -
14 K77 18LG/BK TRANSFER CASE POSITION SENSOR INPUT
15 K21 18BK/RD INTAKE AIR TEMPERATURE SENSOR SIGNAL
16 K2 18TN/BK ENGINE COOLANT TEMPERATURE SENSOR SIGNAL
17 K7 18OR 5 VOLT SUPPLY
18 K44 18TN/YL CAMSHAFT POSITION SENSOR SIGNAL
19 K39 18GY/BK IDLE AIR CONTROL NO. 1 DRIVER
20 K59 18VT/BK IDLE AIR CONTROL NO. 4 DRIVER
21 K95 14TN/DG (4.7L) COIL DRIVER NO. 5
22 A7 14RD/BK FUSED B(+)
23 K22 18OR/RD THROTTLE POSITION SENSOR SIGNAL
24 K41 18BK/DG OXYGEN SENSOR 1/1 SIGNAL
25 K141 18TN/WT OXYGEN SENSOR 1/2 SIGNAL
26 K241 18LG/RD (EXCEPT 4.0L
BUILT-UP-EXPORT)OXYGEN SENSOR 2/1 SIGNAL
27 K1 18DG/RD MAP SENSOR SIGNAL
28 - -
29 K341 18TN/WT (4.0L EXCEPT
BUILT-UP-EXPORT)OXYGEN SENSOR 2/2 SIGNAL
29 K341 18PK/WT (4.7L) OXYGEN SENSOR 2/2 SIGNAL
30 - -
31 Z82 14BK/WT GROUND
32 Z81 14BK/TN GROUND
8W - 80 - 108 8W-80 CONNECTOR PIN-OUTWJ

CONNECTOR NAME/
NUMBERCOLOR LOCATION FIG.
Fuel Pump Module (Gas) BK Near Fuel Tank 33, 35
Fuel Tank Module Diesel) BK Near Fuel Tank 33, 35
Generator (Diesel) LTGY At Generator 8
Generator (Gas) BK At Generator N/S
Glove Box Lamp BK Inside Glove Box 19, 20, 22
Headlamp Leveling Switch
(Built-Up-Export)WT Driver Side of Instrument Panel 20
Hood Ajar Switch BK Left Side of Engine Compartment 3, 4
Horn No.1 BK Right Front Fascia 5
Horn No.2 BK Right Front Fascia 5
Hydraulic Cooling Module BK Right Front of Engine Compartment 5
Idle Air Control Motor BK Left Side of Engine Near Throttle
Body13
Ignition Switch - C1 WT On Steering Column 23
Ignition Switch - C2 BK On Steering Column 23
Input Speed Sensor (4.7L) BK Left Side of Transmission 16
Instrument Cluster WT At Instrument Cluster 19, 20
Intake Air Temperature Sensor
(Gas)GY Left Side of Engine 9, 13
Intake Air Temperature Sensor
(Diesel)BK Near T/O for Crankcase Heater 8
Intake Port Swirl Actuator
(Diesel)BK Right Rear of Engine Compartment N/S
Intrusion Transceiver Module
(Built-up-Export)BK In The Overhead N/S
Junction Block - C1 BK At Junction Block 30, 31, 33
Junction Block - C2 BK At Junction Block 30, 31
Junction Block - C3 BK At Junction Block 21, 22, 30
Junction Block - C4 WT At Junction Block 30, 31
Junction Block - C5 WT At Junction Block 30, 31
Knock Sensor (4.7L High
Output)BK Right Rear Side of Engine, Near
Coil on Plug No.8N/S
Leak Detection Pump (Except
Built-Up-Export)Left Front Wheel Opening 3
Left Courtesy Lamp BK Left Side of Instrument Panel 21 22, 23
Left Curtain Airbag BK Near Left C Pillar 37
Left Door Handle Courtesy
LampBK At Lamp N/S
Left Fog Lamp BK At Lamp 3, 4
Left Front Door Speaker WT In Left Front Door 24, 27
Left Front Impact Sensor BK Left Front Frame Near Windshield
Washer Pump3, 4
Left Front Park Lamp WT At Lamp N/S
8W - 91 - 6 8W-91 CONNECTOR/GROUND/SPLICE LOCATIONWJ
CONNECTOR/GROUND/SPLICE LOCATION (Continued)

the same time, the power distribution system was
designed to provide ready access to these electrical
distribution points for the vehicle technician to use
when conducting diagnosis and repair of faulty cir-
cuits. The power distribution system can also prove
useful for the sourcing of additional electrical circuits
that may be required to provide the electrical current
needed to operate accessories that the vehicle owner
may choose to have installed in the aftermarket.
NOTE: DO NOT ATTEMPT TO SWAP POWER DIS-
TRIBUTION CENTERS FROM ONE VEHICLE TO
ANOTHER. MOST OF THESE ASSEMBLIES ARE
VEHICLE FEATURE SPECIFIC AND THEREFORE
NOT INTERCHANGEABLE. ALWAYS USE THE COR-
RECT PART NUMBERED ASSEMBLY WHEN DIAG-
NOSING OR REPLACING A POWER DISTRIBUTION
CENTER.
SPECIAL TOOLS
POWER DISTRIBUTION SYSTEMS
CIGAR LIGHTER OUTLET
DESCRIPTION
A cigar lighter outlet is standard equipment on
this model. On models equipped with the optional
Smoker's Package, the cigar lighter knob and heating
element are included. On models without the Smok-
er's Package, the cigar lighter outlet is equipped with
a snap fit plastic cap and is treated as an extra
accessory power outlet. The cigar lighter outlet is
installed in the instrument panel center lower bezel,
which is located near the bottom of the instrument
panel center stack area, below the heater and air
conditioner controls. The cigar lighter outlet is
secured by a snap fit within the center lower bezel.The cigar lighter outlet, plastic cap and the knob
and heating element unit are available for service
replacement. These components cannot be repaired
and, if faulty or damaged, they must be replaced.
OPERATION
The cigar lighter consists of two major components:
a knob and heating element unit, and the cigar
lighter base or outlet shell. The receptacle shell is
connected to ground, and an insulated contact in the
bottom of the shell is connected to battery current.
The cigar lighter receives battery voltage from a fuse
in the junction block when the ignition switch is in
the Accessory or On positions.
The cigar lighter knob and heating element are
encased within a spring-loaded housing, which also
features a sliding protective heat shield. When the
knob and heating element are inserted in the outlet
shell, the heating element resistor coil is grounded
through its housing to the outlet shell. If the cigar
lighter knob is pushed inward, the heat shield slides
up toward the knob exposing the heating element,
and the heating element extends from the housing
toward the insulated contact in the bottom of the
outlet shell.
Two small spring-clip retainers are located on
either side of the insulated contact inside the bottom
of the outlet shell. These clips engage and hold the
heating element against the insulated contact long
enough for the resistor coil to heat up. When the
heating element is engaged with the contact, battery
current can flow through the resistor coil to ground,
causing the resistor coil to heat.
When the resistor coil becomes sufficiently heated,
excess heat radiates from the heating element caus-
ing the spring-clips to expand. Once the spring-clips
expand far enough to release the heating element,
the spring-loaded housing forces the knob and heat-
ing element to pop back outward to their relaxed
position. When the cigar lighter knob and element
are pulled out of the outlet shell, the protective heat
shield slides downward on the housing so that the
heating element is recessed and shielded around its
circumference for safety.
DIAGNOSIS AND TESTING - CIGAR LIGHTER
OUTLET
For complete circuit diagrams, refer toHorn/Ci-
gar Lighter/Power Outletin Wiring Diagrams.
(1) Check the fused B(+) fuse in the junction block.
If OK, go to Step 2. If not OK, repair the shorted cir-
cuit or component as required and replace the faulty
fuse.
(2) Turn the ignition switch to the On position.
Check for battery voltage at the fused B(+) fuse in
Terminal Pick Kit 6680
8W - 97 - 2 8W-97 POWER DISTRIBUTIONWJ
POWER DISTRIBUTION (Continued)

The cigar lighter relay cannot be repaired or
adjusted and, if faulty or damaged, it must be
replaced.
OPERATION
The ISO relay consists of an electromagnetic coil, a
resistor or diode, and three (two fixed and one mov-
able) electrical contacts. The movable (common feed)
relay contact is held against one of the fixed contacts
(normally closed) by spring pressure. When the elec-
tromagnetic coil is energized, it draws the movable
contact away from the normally closed fixed contact,
and holds it against the other (normally open) fixed
contact.
When the electromagnetic coil is de-energized,
spring pressure returns the movable contact to the
normally closed position. The resistor or diode is con-
nected in parallel with the electromagnetic coil in the
relay, and helps to dissipate voltage spikes that are
produced when the coil is de-energized.
DIAGNOSIS AND TESTING - POWER OUTLET
RELAY
The power outlet / cigar lighter relay (Fig. 16) is
located in the junction block, below the driver side
end of the instrument panel in the passenger com-
partment. For complete circuit diagrams, refer to
Horn/Cigar Lighter/Power Outletin Wiring Dia-
grams.
WARNING: REFER TO RESTRAINTS BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, OR INSTRUMENT PANEL COMPONENT
DIAGNOSIS OR SERVICE. FAILURE TO TAKE THE
PROPER PRECAUTIONS COULD RESULT IN ACCI-
DENTAL AIRBAG DEPLOYMENT AND POSSIBLE
PERSONAL INJURY.
(1) Remove the power outlet / cigar lighter relay
from the junction block. Refer to the procedure in
this group.
(2) A relay in the de-energized position should
have continuity between terminals 87A and 30, and
no continuity between terminals 87 and 30. If OK, go
to Step 3. If not OK, replace the faulty relay.
(3) Resistance between terminals 85 and 86 (elec-
tromagnet) should be 75   5 ohms. If OK, go to Step
4. If not OK, replace the faulty relay.
(4) Connect a battery to terminals 85 and 86.
There should now be continuity between terminals
30 and 87, and no continuity between terminals 87A
and 30. If OK, perform the Relay Circuit Test that
follows. If not OK, replace the faulty relay.
DIAGNOSIS AND TESTING - RELAY CIRCUIT TEST
(1) The relay common feed terminal cavity (30) of
the junction block is connected to battery voltage and
should be hot at all times. Check for battery voltage
at the fused B(+) circuit cavity in the junction block
receptacle for the cigar lighter relay. If OK, go to
Step 2. If not OK, repair the fused B(+) circuit to the
Power Distribution Center (PDC) fuse as required.
(2) The relay normally closed terminal (87A) is
connected to terminal 30 in the de-energized position,
but is not used for this application. Go to Step 3.
(3) The relay normally open terminal (87) is con-
nected to the common feed terminal (30) in the ener-
gized position. This terminal supplies battery voltage
to the fused B(+) fuse in the junction block that feeds
the cigar lighter when the relay is energized by the
ignition switch. There should be continuity between
the junction block cavity for relay terminal 87 and
the fused B(+) fuse in the junction block at all times.
If OK, go to Step 4. If not OK, repair the open fused
B(+) circuit to the junction block fuse as required.
(4) The coil ground terminal (85) is connected to
the electromagnet in the relay. It receives battery
feed to energize the cigar lighter relay when the igni-
tion switch is in the Accessory or On positions. Turn
the ignition switch to the On position. Check for bat-
tery voltage at the fused ignition switch output (acc/
run) circuit cavity for relay terminal 85 in the
junction block receptacle for the cigar lighter relay. If
OK, go to Step 5. If not OK, repair the open fused
ignition switch output (acc/run) circuit to the ignition
switch as required.
(5) The coil battery terminal (86) is connected to
the electromagnet in the relay. The junction block
cavity for this terminal should have continuity to
Fig. 16 Accessory Relay
TERMINAL LEGEND
NUMBER IDENTIFICATION
30 COMMON FEED
85 COIL GROUND
86 COIL BATTERY
87 NORMALLY OPEN
87A NORMALLY CLOSED
8W - 97 - 14 8W-97 POWER DISTRIBUTIONWJ
POWER OUTLET RELAY (Continued)

CONDITION POSSIBLE CAUSES CORRECTION
3. Worn or incorrect gapped spark
plugs3. Clean plugs and set gap. (Refer to
8 - ELECTRICAL/IGNITION
CONTROL/SPARK PLUG -
CLEANING).
4. Dirt or water in fuel system 4. Clean system and replace fuel
filter
5. Faulty fuel pump 5. Install new fuel pump
6. Incorrect valve timing 6. Correct valve timing
7. Blown cylinder head gasket 7. Install new cylinder head gasket
8. Low compression 8. Test cylinder compression. (Refer
to 9 - ENGINE - DIAGNOSIS AND
TESTING).
9. Burned, warped, or pitted valves 9. Install/Reface valves as necessary
10. Plugged or restricted exhaust
system10. Install new parts as necessary
11. Faulty ignition coil rail 11. Test and replace, as necessary.
(Refer to 8 - ELECTRICAL/IGNITION
CONTROL/COIL RAIL - REMOVAL).
ENGINE STALLS OR ROUGH
IDLE1. Carbon build-up on throttle plate 1. Remove throttle body and
de-carbon. (Refer to 14 - FUEL
SYSTEM/FUEL INJECTION/
THROTTLE BODY - REMOVAL) for
correct procedure.
2. Engine idle speed too low 2. Check Idle Air Control circuit.
3. Worn or incorrectly gapped spark
plugs3. Replace or clean and re-gap spark
plugs. (Refer to 8 - ELECTRICAL/
IGNITION CONTROL/SPARK PLUG
- CLEANING)
4. Faulty coil rail 4. Test and replace, if necessary.
(Refer to 8 - ELECTRICAL/IGNITION
CONTROL/COIL RAIL - REMOVAL)
5. Intake manifold vacuum leak 5. Inspect intake manifold gasket and
vacuum hoses. Replace if necessary.
(Refer to 9 - ENGINE/MANIFOLDS/
INTAKE MANIFOLD - DIAGNOSIS
AND TESTING).
ENGINE MISSES ON
ACCELERATION1. Worn or incorrectly gapped spark
plugs1. Replace spark plugs or clean and
set gap.
2. Spark plug cables defective or
crossed2. Replace spark plug cables.
3. Dirt in fuel system 3. Clean fuel system
4. Burned, warped or pitted valves 4. Install new valves
5. Faulty coil rail 5. Test and replace as necessary.
(Refer to 8 - ELECTRICAL/IGNITION
CONTROL/COIL RAIL - REMOVAL)
WJENGINE - 4.0L 9 - 5
ENGINE - 4.0L (Continued)

DIAGNOSIS AND TESTINGÐCYLINDER
COMPRESSION PRESSURE
The results of a cylinder compression pressure test
can be utilized to diagnose several engine malfunc-
tions.
Ensure the battery is completely charged and the
engine starter motor is in good operating condition.
Otherwise, the indicated compression pressures may
not be valid for diagnosis purposes.
(1) Clean the spark plug recesses with compressed
air.
(2) Remove the spark plugs (Refer to 8 - ELEC-
TRICAL/IGNITION CONTROL/SPARK PLUG -
REMOVAL).
(3) Secure the throttle in the wide-open position.
(4) Disconnect the ignition coil.
(5) Insert a compression pressure gauge and rotate
the engine with the engine starter motor for three
revolutions.
(6) Record the compression pressure on the third
revolution. Continue the test for the remaining cylin-
ders.
(Refer to 9 - ENGINE - SPECIFICATIONS) for the
correct engine compression pressures.
DIAGNOSIS AND TESTING - CYLINDER
COMBUSTION PRESSURE LEAKAGE
The combustion pressure leakage test provides an
accurate means for determining engine condition.
Combustion pressure leakage testing will detect:
²Exhaust and intake valve leaks (improper seat-
ing)
²Leaks between adjacent cylinders or into water
jacket²Any causes for combustion/compression pressure
loss
WARNING: DO NOT REMOVE THE RADIATOR CAP
WITH THE SYSTEM HOT AND UNDER PRESSURE.
SERIOUS BURNS FROM HOT COOLANT CAN
OCCUR.
Check the coolant level and fill as required. DO
NOT install the radiator cap.
Start and operate the engine until it attains nor-
mal operating temperature, then turn OFF the
engine.
Remove the spark plugs.
Remove the oil filler cap.
Remove the air cleaner.
Calibrate the tester according to the manufactur-
er's instructions. The shop air source for testing
should maintain 483 kPa (70 psi) minimum, 1,379
kPa (200 psi) maximum and 552 kPa (80 psi) recom-
mended.
Perform the test procedure on each cylinder accord-
ing to the tester manufacturer's instructions. While
testing, listen for pressurized air escaping through
the throttle body, tailpipe or oil filler cap opening.
Check for bubbles in the radiator coolant.
All gauge pressure indications should be equal,
with no more than 25% leakage.
FOR EXAMPLE:At 552 kPa (80 psi) input pres-
sure, a minimum of 414 kPa (60 psi) should be main-
tained in the cylinder CYLINDER COMBUSTION
PRESSURE LEAKAGE DIAGNOSIS CHART .
CYLINDER COMBUSTION PRESSURE LEAKAGE DIAGNOSIS CHART
CONDITION POSSIBLE CAUSE CORRECTION
AIR ESCAPES THROUGH
THROTTLE BODYIntake valve bent, burnt, or not
seated properlyInspect valve and valve seat.
Reface or replace, as necessary
AIR ESCAPES THROUGH
TAILPIPEExhaust valve bent, burnt, or not
seated properlyInspect valve and valve seat.
Reface or replace, as necessary
AIR ESCAPES THROUGH
RADIATORHead gasket leaking or cracked
cylinder head or blockRemove cylinder head and inspect.
Replace defective part
MORE THAN 50% LEAKAGE
FROM ADJACENT CYLINDERSHead gasket leaking or crack in
cylinder head or block between
adjacent cylindersRemove cylinder head and inspect.
Replace gasket, head, or block as
necessary
MORE THAN 25% LEAKAGE AND
AIR ESCAPES THROUGH OIL
FILLER CAP OPENING ONLYStuck or broken piston rings;
cracked piston; worn rings and/or
cylinder wallInspect for broken rings or piston.
Measure ring gap and cylinder
diameter, taper and out-of-round.
Replace defective part as necessary
9 - 8 ENGINE - 4.0LWJ
ENGINE - 4.0L (Continued)