1994 JEEP CHEROKEE engine

With the ignition key in the ON position and en-
gine not running, check the sensor output voltage at
the center terminal wire of the connector. Check this
at idle (throttle plate closed) and at wide open throt-
tle (WOT). At idle, sensor output voltage should be
greater than 200 millivolts. At wide open throttle,
sensor output voltage must be less than 4.8 volts.
The output voltage should increase gradually as the
throttle plate is slowly opened from idle to WOT.
OXYGEN SENSOR TESTS
For diagnosis, removal or installation, refer to
Group 14, Fuel Systems in this manual.
ON-BOARD DIAGNOSTICS (OBD)
FOR IGNITION SYSTEM COMPONENTS
The powertrain control module (PCM) has been
programmed to monitor certain ignition system cir-
cuits:
EXAMPLE:
If a reference signal is not being detected during
engine cranking from the crankshaft position sensor,
a Diagnostic Trouble Code (DTC) number 11 can be
observed at the Check Engine Lamp.
If the problem is sensed in a monitored circuit of-
ten enough to indicate an actual problem, a DTC is
stored. The DTC will be stored in the PCM memory
for eventual display to the service technician. If the
problem is repaired or ceases to exist, the PCM can-
cels the DTC after 51 engine starts.
Certain criteria must be met for a DTC to be en-
tered into PCM memory. The criteria may be a spe-
cific range of engine rpm, engine temperature and/or
input voltage to the PCM.
A DTC indicates that the PCM has recognized an
abnormal signal in a circuit or the system. A DTC
may indicate the result of a failure, but never iden-
tify the failed component directly.
It is possible that a DTC for a monitored circuit
may not be entered into memory even though a mal-
function has occurred. Refer to On-Board Diagnostics
(OBD) in Group 14, Fuel Systems for additional in-
formation.
ACCESSING DIAGNOSTIC TROUBLE CODES
A stored Diagnostic Trouble Code (DTC) can be dis-
played by cycling the ignition key On-Off-On-Off-On
within three seconds and observing the Malfunction
Indicator Lamp. This lamp was formerly referred to
as the Check Engine Lamp. The lamp is located on
the instrument panel.
They can also be displayed through the use of the
Diagnostic Readout Box (DRB) scan tool. The DRB
connects to the data link connector in the enginecompartment (Figs. 32 or 33). For operation of the
DRB, refer to the appropriate Powertrain Diagnostic
Procedures service manual.
EXAMPLES:
²If the lamp flashes 1 time, pauses and flashes 1
more time, a flashing Diagnostic Trouble Code (DTC)
number 11 is indicated.
²If the lamp flashes 3 times, pauses and flashes 5
more times, a flashing Diagnostic Trouble Code
(DTC) number 35 is indicated.
After any stored DTC information has been ob-
served, the display will end with a flashing DTC
number 55. This will indicate the end of all stored
information.
ERASING TROUBLE CODES
After the problem has been repaired, the DRB scan
tool must be used to erase a DTC. Refer to the ap-
propriate Powertrain Diagnostic Procedures service
manual for operation of the DRB scan tool.
Fig. 32 Data Link ConnectorÐYJ ModelsÐTypical
Fig. 33 Data Link ConnectorÐXJ ModelsÐTypical
JIGNITION SYSTEMS 8D - 19

COMPONENT REMOVAL/INSTALLATION
INDEX
page page
Automatic Shut Down (ASD) Relay........... 20
Camshaft Position Sensor.................. 20
Crankshaft Position Sensor................. 21
Distributor.............................. 23
Engine Coolant Temperature Sensor.......... 22
General Information....................... 20
Ignition Coil............................. 26Intake Manifold Air Temperature Sensor....... 27
Manifold Absolute Pressure (MAP) Sensor..... 27
Oxygen (O2S) Sensor..................... 28
Powertrain Control Module (PCM)............ 28
Spark Plug Secondary Cables............... 29
Spark Plugs............................ 28
Throttle Position Sensor (TPS).............. 29
GENERAL INFORMATION
This section of the group, Component Removal/In-
stallation, will discuss the removal and installation
of ignition system components.
For basic ignition system diagnostics and service
adjustments, refer to the Diagnostics/Service Proce-
dures section of this group.
For system operation and component identification,
refer to the Component Identification/System Opera-
tion section of this group.
AUTOMATIC SHUT DOWN (ASD) RELAY
The ASD relay is installed in the Power Distribu-
tion Center (PDC) (Fig. 1). Relay location is printed
on the PDC cover.
REMOVAL
(1) Remove the PDC cover.
(2) Remove the relay by lifting straight up.
INSTALLATION
(1) Check the condition of relay wire terminals at
PDC before installing relay. Repair as necessary.
(2) Push the relay into the connector.
(3) Install the relay cover.
CAMSHAFT POSITION SENSOR
The camshaft position sensor is located in the dis-
tributor.
REMOVAL
(1) Remove the distributor. Refer to Distributor
Removal.
(2) Remove the distributor rotor.
CAUTION: Do not position the distributor in a vise
when removing or installing the drive gear roll pin.
Support the distributor with wooden blocks.
(3) Mark the position of the gear and the shaft in
line with the roll pin. The gearMUSTbe installed
back to its original position on the distributor shaft.
(4) Using a small pin punch and hammer, remove
the distributor gear roll (spring) pin (Fig. 3).
(5) Lightly tap the end of the distributor shaft un-
til distributor gear and thrust washer are removed.
(6) Slide the distributor shaft out of the distributor
housing.
(7) Remove the camshaft position sensor mounting
screw and positioning arm (Fig. 4).
(8) Slide the wire harness grommet out of the dis-
tributor housing. Remove the camshaft position sen-
sor.
Fig. 1 PDCÐXJ Models
Fig. 2 PDCÐYJ Models
8D - 20 IGNITION SYSTEMSJ

INSTALLATION
(1) Position the camshaft position sensor in the
distributor housing. Place the wire harness grommet
into the opening in the distributor housing.
(2) Install retaining arm and retaining screw.
(3) Install distributor shaft into distributor hous-
ing. Make sure the upper thrust washer is installed
on the shaft.
(4) Position thrust washer and drive gear on dis-
tributor shaft.
(5) Note the previousCAUTIONand install dis-
tributor drive gear roll pin.
(6) Install rotor.
(7) Install distributor.
CRANKSHAFT POSITION SENSOR
The crankshaft position sensor is mounted in thetransmission bellhousing at the left/rear side of the
engine block (Figs. 5, 6 or 7).
On all 2.5L and 4.0L engines (except YJ models
with an automatic transmission and 4.0L engine) the
sensor is attached with two bolts. The 2.5L engine,
when equipped with an automatic transmission, will
have the sensor mounted with two nuts.
On YJ models with a 4.0L engine and automatic
transmission, the sensor uses a single slotted hole to
adjust its depth. A paper/cardboard type spacer with
self-adhesive (Fig. 7) is attached to the bottom of the
sensor to set this depth. After the engine has been
started (and after sensor installation), this temporary
spacer will be sheared off. New factory replacement
sensors are equipped with this spacer. If the original
sensor is to be reinstalled, such as with transmission
and/or flywheel removal, a new spacerMUSTbe in-
stalled.
Fig. 3 Distributor GearÐRemoval/Installation
Fig. 4 Camshaft Position Sensor
Fig. 5 Crankshaft Position SensorÐ2.5L
EngineÐTypical
Fig. 6 Crankshaft Position SensorÐ4.0L EngineÐAll
Except YJ models With Automatic Transmission
JIGNITION SYSTEMS 8D - 21

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 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.
CAUTION: On some models, two bolts used to se-
cure 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
ENGINE AND AUTOMATIC TRANSMISSION
(1) Be sure the paper/cardboard spacer (Fig. 7) has
been installed to the bottom of the new sensor.If original sensor is being reinstalled (such as with
transmission or flywheel removal), clean bottom of
the sensor before installation. Obtain a new spacer
and remove the paper backing. Install the self-adhe-
sive side to bottom of sensor. This spacerMUSTbe
installed. If spacer is not installed, sensor will be
damaged when engine is started.
(2) Position sensor to transmission bellhousing and
install mounting bolt finger tight.
(3) Gently seat (push down) the sensor until the
paper spacer contacts the outer edge of the flywheel.
(4) Tighten sensor mounting bolt (Fig. 7) to 17-
to-21 Nzm (13-to-16 ft. lbs.) torque.
(5) Connect the electrical connector to sensor.
(6) Install the clip to sensor wire harness.
(7) Install clip over fuel rail mounting stud. Install
clip mounting nut.
ENGINE COOLANT TEMPERATURE SENSOR
WARNING: HOT, PRESSURIZED COOLANT CAN
CAUSE INJURY BY SCALDING. COOLING SYSTEM
MUST BE PARTIALLY DRAINED BEFORE REMOV-
ING THE COOLANT TEMPERATURE SENSOR. RE-
FER TO GROUP 7, COOLING.
REMOVAL
The sensor is installed in the thermostat housing
(Fig. 8).
(1) Drain cooling system until the coolant level is
below the cylinder head. For cooling system draining,
refer to Group 7, Cooling.
(2) Disconnect the coolant temperature sensor wire
connector.
(3) Remove the sensor from the thermostat hous-
ing (Fig. 8).
Fig. 7 Crankshaft Position SensorÐ4.0L EngineÐYJ
models With Automatic Transmission
Fig. 8 Coolant Temperature SensorÐTypical
8D - 22 IGNITION SYSTEMSJ

INSTALLATION
(1) Install coolant temperature sensor into the
thermostat housing. Tighten to 28 Nzm (21 ft. lbs.)
torque.
(2) Connect the wire connector.
(3) Fill the cooling system. Refer to group 7, Cool-
ing System.
DISTRIBUTOR
All distributors contain an internal oil seal that
prevents oil from entering the distributor housing.
The seal is not serviceable.
The camshaft position sensor is located in the dis-
tributor on all engines (Fig. 9).
Refer to Fig. 9 for an exploded view of the distrib-
utor.
REMOVALÐ2.5L ENGINE
(1) Disconnect the negative battery cable at the
battery.
(2) Disconnect coil secondary cable at coil.
(3) Remove distributor cap from distributor (2
screws). Do not remove cables from cap.
(4) Disconnect the distributor wiring harness from
the main engine harness.
(5) Scribe a mark on the distributor housing in
line with the tip of the rotor. Note the position of the
rotor and distributor housing. This is in relation tothe surrounding engine components as reference
points for installing the distributor.
(6) Remove the distributor holddown bolt and
clamp.
(7) Remove the distributor from engine by lifting
straight up. Remove and discard old distributor-to-
engine block gasket. Note that the rotor will rotate
slightly in a counterclockwise direction while lifting
up the distributor. Note this position after removal.
INSTALLATIONÐ2.5L ENGINE
ENGINE NOT ROTATED AFTER REMOVAL
This procedure assumes that the engine was not ro-
tated with distributor out of engine.
(1) Clean the distributor mounting hole area of the
engine block.
(2) Install a new distributor-to-engine block gas-
ket.
There is a fork on the distributor housing where
the housing seats against the engine block. The slot
in the fork aligns with the distributor holddown bolt
hole in the engine block. The distributor is correctly
installed when the rotor is correctly positioned. This
is with the slot in the fork aligned with the hold-
down bolt hole in the cylinder block. Because of the
fork on the distributor housing, initial ignition tim-
ing is not adjustable (the distributor cannot be rotat-
ed).
(3) Position the distributor shaft in the cylinder
block. If the engine was not rotated while the distrib-
utor was removed, perform the following:
²Align the rotor tip with the scribe mark on the
distributor housing during removal. Turn the rotor
approximately 1/8-turn counterclockwise past the
scribe mark.
CAUTION: Be sure that the distributor shaft fully
engages into the oil pump drive gear shaft. It may
be necessary to slightly rotate (bump) the engine.
This is done while applying downward hand force
on the distributor body. It should fully engage the
distributor shaft with the oil pump drive gear shaft.
²Slide the distributor shaft down into the engine.
It may be necessary to move the rotor and shaft
(slightly) to engage the distributor shaft with the slot
in the oil pump shaft. The same may have to be done
to engage the distributor gear with the camshaft
gear. However, the rotor should align with the scribe
mark when the distributor shaft is down in place.
²Install the distributor holddown clamp and bolt.
Tighten the bolt to 23 Nzm (17 ft. lbs.) torque.
(4) Install the distributor cap (with the ignition ca-
bles) on the distributor housing (Fig. 10). Tighten
distributor cap holddown screws to 3 Nzm (26 in. lbs.)
torque.
(5) Connect the distributor wiring harness to the
main engine harness.
Fig. 9 DistributorÐ2.5L/4.0L EnginesÐTypical
JIGNITION SYSTEMS 8D - 23

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

The camshaft position sensor is located in the dis-
tributor on all engines (Fig. 9).
Refer to figure 9 for an exploded view of the dis-
tributor.
(1) Disconnect the negative battery cable at bat-
tery.
(2) On XJ models equipped with A/C, remove the
electrical cooling fan and shroud assembly from the
radiator. This will provide room to turn the engine
with a socket and ratchet using the vibration damper
bolt.
(3) Scribe a mark on the distributor housing. Do
this below the left side of (past) the number one
spark plug cable post of the distributor cap. This will
be used as a reference for #1 cylinder firing position
(Fig. 14).
(4) Remove the distributor cap from distributor (2
screws).
(5) Turn the engine in a clockwise direction until
the rotor is approaching the scribe mark on the dis-
tributor housing. Then slowly turn the engine until
the timing mark on the crankshaft vibration damper
lines up with zero on the front cover timing scale
(Fig. 15).
The timing mark is on the edge of the vibra-
tion damper closest to the engine front cover.
(6) Align the trailing edge of the rotor blade with
the scribe mark on the distributor housing (Fig. 16).
(7) Remove the distributor holddown bolt and
clamp.
(8) Remove the distributor from the engine by lift-
ing straight up. Remove and discard old distributor-
to-engine block gasket. Note that the rotor willrotate slightly in a counterclockwise direction while
lifting up the distributor. Note this position after re-
moval.
INSTALLATIONÐ4.0L ENGINE
(1) Clean the distributor mounting area of the cyl-
inder block.
(2) Install a replacement distributor-to-engine
block gasket.
(3) Using a flat blade screwdriver, turn the oil
pump gear shaft. Do this until the slot is slightly
past the 11 o'clock position (Fig. 17).
Fig. 13 Distributor Rotor PositionÐ2.5L EngineFig. 14 Mark Distributor Housing
Fig. 15 Align Timing Marks
JIGNITION SYSTEMS 8D - 25

The oil pump shaft is located down in the distribu-
tor hole.
(4) Install the rotor.
(5) Without engaging the distributor gear into the
cam gear, position the distributor into the hole in the
engine block. Be sure the distributor gasket is in-
stalled.
(6) Visually line up the holddown ear of the dis-
tributor housing with the holddown clamp hole (Fig.
18).
(7) Turn the rotor to the 4 o'clock position (Fig.
19).
(8) Slide the distributor down into the block until
it seats. Keep the holddown ear aligned to the hole
in the block.
(9) The rotor should be in the 5 o'clock position.
This is with the trailing edge of rotor blade lined up
with scribe mark on distributor housing (number one
spark plug cable post location).(10) Install the distributor holddown clamp bolt
and tighten to 23 Nzm (17 ft. lbs.) torque.
(11) Install the distributor cap and connect the dis-
tributor electrical connector.
(12) Install electrical cooling fan and shroud if ap-
plicable.
(13) Connect battery cable to battery.
IGNITION COIL
The ignition coil is an epoxy filled type. If the coil
is replaced, it must be replaced with the same type.
Fig. 16 Align Rotor Trailing Edge With Scribe Mark
Fig. 17 Align Oil Pump Gear ShaftÐ4.0L Engine
Fig. 18 Distributor InstallationÐTypical
Fig. 19 Rotor Alignment
8D - 26 IGNITION SYSTEMSJ