1995 JEEP YJ fuel

IGNITION COIL
To perform a complete test of the ignition coil and
its circuitry, refer to the DRB scan tool. Also refer tothe appropriate Powertrain Diagnostics Procedures
manual. To test the coil only, refer to the following:
The ignition coil (Fig. 11) is designed to operate
without an external ballast resistor.
Inspect the ignition coil for arcing. Test the coil ac-
cording to coil tester manufacturer's instructions.
Test the coil primary and secondary resistance. Re-
place any coil that does not meet specifications. Refer
to the Ignition Coil Resistance chart.
If the ignition coil is being replaced, the secondary
spark plug cable must also be checked. Replace cable
if it has been burned or damaged.
Arcing at the tower will carbonize the cable nipple,
which if it is connected to a new ignition coil, will
cause the coil to fail.
If the secondary coil cable shows any signs of dam-
age, it should be replaced with a new cable and new
terminal. Carbon tracking on the old cable can cause
arcing and the failure of a new ignition coil.
ENGINE COOLANT TEMPERATURE SENSOR TEST
For an operational description, diagnosis and re-
moval/installation procedures, refer to Group 14,
Fuel System.
IGNITION COIL RESISTANCE
Fig. 9 Firing OrderÐ4.0L 6-Cylinder Engine
Fig. 10 Rotor InspectionÐTypical
Fig. 11 Ignition CoilÐTypical (4.0L Shown)
JIGNITION SYSTEMS 8D - 9

(4) Crank the engine for 5 seconds while monitor-
ing the voltage at the coil positive terminal:
²If the voltage remains near zero during the entire
period of cranking, refer to On-Board Diagnostics in
Group 14, Fuel Systems. Check the powertrain con-
trol module (PCM) and auto shutdown relay.
²If voltage is at or near battery voltage and drops
to zero after 1-2 seconds of cranking, check the cam-
shaft position sensor-to-PCM circuit. Refer to On-
Board Diagnostics in Group 14, Fuel Systems.
²If voltage remains at or near battery voltage dur-
ing the entire 5 seconds, turn the key off. Remove
the 60-way connector (Fig. 15) from the PCM. Check
60-way connector for any spread terminals.
(5) Remove test lead from the coil positive termi-
nal. Connect an 18 gauge jumper wire between the
battery positive terminal and the coil positive termi-
nal.
(6) Make the special jumper shown in figure 16.
Using the jumper,momentarilyground pin/cavity
number 19 of the PCM 60-way connector. A spark
should be generated at the coil cable when the
ground is removed.
(7) If spark is generated, replace the powertrain
control module (PCM).
(8) If spark is not seen, use the special jumper to
ground the coil negative terminal directly.
(9) If spark is produced, repair wiring harness for
an open condition.
(10) If spark is not produced, replace the ignition
coil.IGNITION TIMING
Base (initial) ignition timing is NOT adjust-
able on any of the 2.5L 4-cylinder or 4.0L 6-cyl-
inder engines. Do not attempt to adjust ignition
timing by rotating the distributor.
Do not attempt to modify the distributor
housing to get distributor rotation. Distributor
position will have no effect on ignition timing.
All ignition timing functions are controlled by the
powertrain control module (PCM). Refer to On-Board
Diagnostics in the Multi-Port Fuel InjectionÐGen-
eral Diagnosis section of Group 14, Fuel Systems for
more information. Also refer to the appropriate Pow-
ertrain Diagnostics Procedures service manual for op-
eration of the DRB Scan Tool.
INTAKE MANIFOLD AIR TEMPERATURE SENSOR
TEST
For an operational description, diagnosis or remov-
al/ installation procedures, refer to Group 14, Fuel
Systems.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
TEST
For an operational description, diagnosis and re-
moval/installation procedures, refer to Group 14,
Fuel System.
POWERTRAIN CONTROL MODULE (PCM)
The PCM (formerly referred to as the SBEC or en-
gine controller) is located in the engine compartment
behind the windshield washer fluid tank on YJ mod-
els (Fig. 17). It is located in the engine compartment
next to the air cleaner on XJ models (Fig. 18).
The ignition system is controlled by the PCM.
For removal and installation of this component, re-
fer to the Component Removal/Installation section of
this group.
Fig. 15 PCM 60-Way Connector
Fig. 16 Special Jumper Ground-to-Coil Negative
Terminal
Fig. 17 PCM LocationÐYJ Models
JIGNITION SYSTEMS 8D - 11

For diagnostics, refer to the appropriate Powertrain
Diagnostic Procedures service manual for operation
of the DRB scan tool.
SPARK PLUGS
For spark plug removal, cleaning, gap adjustment
and installation, refer to the Component Removal/In-
stallation section of this group.
Faulty carbon and/or gas fouled plugs generally
cause hard starting, but they will clean up at higher
engine speeds. Faulty plugs can be identified in a
number of ways: poor fuel economy, power loss, de-
crease in engine speed, hard starting and, in general,
poor engine performance.
Remove the spark plugs and examine them for
burned electrodes and fouled, cracked or broken por-
celain insulators. For identification, keep plugs ar-
ranged in the order in which they were removed from
the engine. An isolated plug displaying an abnormal
condition indicates that a problem exists in the cor-
responding cylinder. Replace spark plugs at the inter-
vals recommended in the maintenance chart in
Group 0, Lubrication and Maintenance.
Spark plugs that have low mileage may be cleaned
and reused if not otherwise defective. Refer to the
following Spark Plug Condition section of this group.
CONDITION
NORMAL OPERATING
The few deposits present on the spark plug will
probably be light tan or slightly gray in color. This is
evident with most grades of commercial gasoline
(Fig. 19). There will not be evidence of electrode
burning. Gap growth will not average more than ap-
proximately 0.025 mm (.001 in) per 1600 km (1000
miles) of operation. Spark plugs that have normal
wear can usually be cleaned, have the electrodes
filed, have the gap set and then be installed.Some fuel refiners in several areas of the United
States have introduced a manganese additive (MMT)
for unleaded fuel. During combustion, fuel with MMT
causes the entire tip of the spark plug to be coated
with a rust colored deposit. This rust color can be
misdiagnosed as being caused by coolant in the com-
bustion chamber. Spark plug performance is not af-
fected by MMT deposits.
COLD FOULING/CARBON FOULING
Cold fouling is sometimes referred to as carbon
fouling. The deposits that cause cold fouling are ba-
sically carbon (Fig. 19). A dry, black deposit on one or
two plugs in a set may be caused by sticking valves
or defective spark plug cables. Cold (carbon) fouling
of the entire set of spark plugs may be caused by a
clogged air cleaner element or repeated short operat-
ing times (short trips).
WET FOULING OR GAS FOULING
A spark plug coated with excessive wet fuel or oil is
wet fouled. In older engines, worn piston rings, leak-
ing valve guide seals or excessive cylinder wear can
cause wet fouling. In new or recently overhauled en-
gines, wet fouling may occur before break-in (normal
oil control) is achieved. This condition can usually be
resolved by cleaning and reinstalling the fouled
plugs.
OIL OR ASH ENCRUSTED
If one or more spark plugs are oil or oil ash en-
crusted (Fig. 20), evaluate engine condition for the
cause of oil entry into that particular combustion
chamber.
ELECTRODE GAP BRIDGING
Electrode gap bridging may be traced to loose de-
posits in the combustion chamber. These deposits ac-
cumulate on the spark plugs during continuous stop-
and-go driving. When the engine is suddenly
Fig. 18 PCM LocationÐXJ ModelsFig. 19 Normal Operation and Cold (Carbon) Fouling
8D - 12 IGNITION SYSTEMSJ

subjected to a high torque load, deposits partially liq-
uefy and bridge the gap between electrodes (Fig. 21).
This short circuits the electrodes. Spark plugs with
electrode gap bridging can be cleaned using standard
procedures.
SCAVENGER DEPOSITS
Fuel scavenger deposits may be either white or yel-
low (Fig. 22). They may appear to be harmful, but
this is a normal condition caused by chemical addi-
tives in certain fuels. These additives are designed to
change the chemical nature of deposits and decrease
spark plug misfire tendencies. Notice that accumula-
tion on the ground electrode and shell area may be
heavy, but the deposits are easily removed. Sparkplugs with scavenger deposits can be considered nor-
mal in condition and can be cleaned using standard
procedures.
CHIPPED ELECTRODE INSULATOR
A chipped electrode insulator usually results from
bending the center electrode while adjusting the
spark plug electrode gap. Under certain conditions,
severe detonation can also separate the insulator
from the center electrode (Fig. 23). Spark plugs with
this condition must be replaced.
PREIGNITION DAMAGE
Preignition damage is usually caused by excessive
combustion chamber temperature. The center elec-
trode dissolves first and the ground electrode dis-
solves somewhat latter (Fig. 24). Insulators appear
relatively deposit free. Determine if the spark plug
has the correct heat range rating for the engine. De-
termine if ignition timing is over advanced, or if
other operating conditions are causing engine over-
heating. (The heat range rating refers to the operat-
ing temperature of a particular type spark plug.
Spark plugs are designed to operate within specific
Fig. 20 Oil or Ash Encrusted
Fig. 21 Electrode Gap Bridging
Fig. 22 Scavenger Deposits
Fig. 23 Chipped Electrode Insulator
JIGNITION SYSTEMS 8D - 13

To test ignition coil-to-distributor cap cable, do not
remove the cable from the cap. Connect ohmmeter to
rotor button (center contact) of distributor cap and
terminal at ignition coil end of cable. If resistance is
not within specifications as found in the Spark Plug
Cable Resistance chart, remove the cable from the
distributor cap. Connect the ohmmeter to the termi-
nal ends of the cable. If resistance is not within spec-
ifications as found in the Spark Plug Cable
Resistance chart, replace the cable. Inspect the igni-
tion coil tower for cracks, burns or corrosion.
For removal and installation of spark plug cables,
refer to Spark Plug Secondary Cables in the Compo-
nent Removal/Installation section.
THROTTLE POSITION SENSOR TEST
For an operational description, diagnosis and re-
moval/installation procedures, refer to Group 14,
Fuel System.
OXYGEN (O2S) SENSOR TESTS
For an operational description, diagnosis or remov-
al/ installation procedures, refer to Group 14, Fuel
Systems.
ON-BOARD DIAGNOSTICS
FOR CERTAIN IGNITION SYSTEM
COMPONENTS
The powertrain control module (PCM) performs an
On-Board Diagnostic (OBD) check for certain ignition
system components on all vehicles. This is done by
setting a diagnostic trouble code (DTC).
A DTC can be obtained in two different ways. One
of the ways is by connecting the DRB scan tool to the
data link connector. This connector is located in the
engine compartment (Figs. 26 or 27). Refer to the ap-
propriate Powertrain Diagnostic Procedures service
manual for operation of the DRB scan tool. The other
way is to cycle the ignition key and observe the mal-
function indicator lamp (MIL). The MIL lamp is dis-
played on the instrument panel as the CHECK
ENGINE lamp (Figs. 28 or 29). This lamp will flash
a numeric code. If a numeric code number 11 (for the
crankshaft position sensor) or 42 (for the ASD relay)
is observed, a problem has been found in the ignition
system.
Note that the CHECK ENGINE lamp will illumi-
nate initially for approximately two seconds each
time the ignition key is turned to the ON position.
This is done for a bulb test.
Fig. 26 Data Link ConnectorÐXJ ModelsÐTypical
Fig. 27 Data Link ConnectorÐYJ ModelsÐTypical
JIGNITION SYSTEMS 8D - 15

For a complete operational description of all
DTC's, for accessing a DTC and for erasing aDTC, refer to On-Board Diagnostics. This can
be found in the General Diagnosis sections of
Group 14, Fuel System. For numeric flash lamp
code charts, refer to Diagnostic Trouble Code
(DTC). This can also be found in the General
Diagnosis sections of Group 14, Fuel System.
Fig. 28 Check Engine LampÐXJ ModelsÐTypicalFig. 29 Check Engine LampÐYJ ModelsÐTypical
8D - 16 IGNITION SYSTEMSJ

transmission bellhousing at the left/rear side of the
engine block (Figs. 4, 5 or 6).
On all 2.5L 4-cylinder and 4.0L 6-cylinder engines
(except YJ models with an automatic transmission
and 4.0L 6-cylinder engine) the sensor is attached
with two bolts. The 2.5L 4-cylinder engine, when
equipped with an automatic transmission, will have
the sensor mounted with two nuts.
On YJ models with a 4.0L 6-cylinder engine and
automatic transmission, the sensor is attached with a
single bolt (Fig. 6).
REMOVALÐALL ENGINES
(1) Near the rear of the intake manifold, discon-
nect the pigtail harness (on the sensor) from the
main electrical harness.
(2) Remove the nut holding sensor wire clip to fuel
rail mounting stud.
(3) Depending upon application, remove either the
sensor mounting bolt(s) or nuts.
(4) Remove the sensor.(5) Remove clip from sensor wire harness.
INSTALLATIONÐALL EXCEPT YJ MODELS
WITH 4.0L 6-CYLINDER ENGINE AND
AUTOMATIC TRANSMISSION
(1) Install the sensor flush against the opening in
the transmission housing.
(2) Install and tighten the two sensor mounting
bolts (or nuts) to 19 Nzm (14 ft. lbs.) torque.
Fig. 3 Camshaft Position Sensor
Fig. 4 Crankshaft Position SensorÐ2.5L 4-Cylinder
EngineÐTypical
Fig. 5 Crankshaft Position SensorÐ4.0L 6-Cylinder
EngineÐAll Except YJ models With Automatic
Transmission
Fig. 6 Crankshaft Position SensorÐ4.0L 6-Cylinder
EngineÐYJ models With Automatic Transmission
8D - 18 IGNITION SYSTEMSJ

CAUTION: On some models, two bolts are used to
secure the sensor to the transmission. These bolts
are specially machined to correctly space the unit
to the flywheel. Do not attempt to install any other
bolts.
(3) Connect the electrical connector to the sensor.
(4) Install clip on sensor wire harness.
(5) Install clip over fuel rail mounting stud. Install
clip mounting nut.
INSTALLATIONÐYJ MODELS WITH 4.0L
6-CYLINDER ENGINE AND AUTOMATIC
TRANSMISSION
(1) Install the sensor into the access hole on the
transmission.
(2) Install sensor mounting bolt (Fig. 6).
(3) Tighten sensor mounting bolt to 6-to-8 Nzm (50-
to-70 in. lbs.) torque.
(4) Connect the electrical connector to sensor.
(5) Install the clip to sensor wire harness.
(6) Install clip over fuel rail mounting stud. Install
clip mounting nut.
ENGINE COOLANT TEMPERATURE SENSOR
For an operational description, diagnosis and re-
moval/installation procedures, refer to Group 14,
Fuel System.
DISTRIBUTOR
GENERAL INFORMATION
All distributors contain an internal oil seal that
prevents oil from entering the distributor housing.
The seal is not serviceable.
Factory replacement distributors are equipped with
a plastic alignment pin already installed. The pin is
located in an access hole on the bottom of the distrib-
utor housing (Fig. 7). It is used to temporarily lock
the rotor to the cylinder number 1 position during in-
stallation. The pin must be removed after installing
the distributor.
The camshaft position sensor is located in the dis-
tributor on all engines (Fig. 8). For removal/installa-
tion procedures, refer to Camshaft Position Sensor.
Distributor removal is not necessary for sensor re-
moval.
Refer to figure 8 for an exploded view of the dis-
tributor.
A fork with a slot is supplied on the bottom of the
distributor housing where the housing base seats
against the engine block (Fig. 8). The centerline of
the slot aligns with the distributor holddown bolt
hole in the engine block. Because of the fork, the dis-
tributor cannot be rotated. Distributor rotation is not
necessary as all ignition timing requirements are
handled by the powertrain control module (PCM).The position of the distributor determines fuel syn-
chronization only. It does not determine ignition tim-
ing.
Do not attempt to modify this fork to attain
ignition timing.
Fig. 7 Plastic Alignment Pin
Fig. 8 DistributorÐ2.5L Or 4.0L EnginesÐTypical
JIGNITION SYSTEMS 8D - 19