1994 JEEP CHEROKEE engine oil

stalled, its rotational position can not be changed.
Do not attempt to modify the distributor housing
to get distributor rotation. Distributor position
will have no effect on ignition timing.
All distributors contain an internal oil seal that
prevents oil from entering the distributor housing.
The seal is not serviceable.
For component testing, refer to the Diagnostics/Ser-
vice Procedures section of this group.For removal and installation of this component, re-
fer to the Component Removal/Installation section of
this group.
IGNITION COIL
Battery voltage is supplied to the ignition coil pos-
itive terminal from the ASD relay.
The Powertrain Control Module (PCM) opens and
closes the ignition coil ground circuit for ignition coil
operation.
Base ignition timing is not adjustable.By con-
trolling the coil ground circuit, the PCM is able to
set the base timing and adjust the ignition timing
advance. This is done to meet changing engine oper-
ating conditions.
The ignition coil is not oil filled. The windings are
embedded in an epoxy compound. This provides heat
and vibration resistance that allows the ignition coil
to be mounted on the engine.
The ignition coil is mounted to a bracket on the
side of the engine (Fig. 11).
For component testing, refer to the Diagnostics/Ser-
vice Procedures section of this group.
For removal and installation of this component, re-
fer to the Component Removal/Installation section of
this group.
ENGINE COOLANT TEMPERATURE SENSOR
The engine coolant temperature sensor provides an
input voltage to the Powertrain Control Module
(PCM) relating coolant temperature. The PCM uses
this input, along with inputs from other sensors, to
determine injector pulse width and ignition timing.
Fig. 8 Sensor OperationÐ2.5L Engine
Fig. 9 Sensor OperationÐ4.0L EngineÐAll Except
YJ Models With Automatic Transmission
Fig. 10 Sensor OperationÐ4.0L EngineÐYJ Models
With Automatic Transmission
8D - 4 IGNITION SYSTEMSJ

As coolant temperature varies, the sensor resistance
will change, resulting in a different input voltage to
the PCM.
When the engine is cold, the PCM will operate in
the Open Loop Cycle. It will demand slightly richer
air-fuel mixtures and higher idle speeds, until nor-
mal operating temperatures are reached. Refer to
Modes Of Operation in Group 14, Fuel System for a
description of Open and Closed Loop operation.
This sensor is installed in the thermostat housing
(Fig. 12).
For component testing, refer to the Diagnostics/Ser-
vice Procedures section of this group.
For removal and installation of this component, re-
fer to the Component Removal/Installation section of
this group.
INTAKE MANIFOLD AIR TEMPERATURE SENSOR
The sensor element extends into the intake mani-
fold air stream. It provides an input voltage to the
Powertrain Control Module (PCM) indicating intakemanifold air temperature. The input from this sensor
is used along with inputs from other sensors to de-
termine injector pulse width. As the temperature of
the air-fuel stream in the manifold varies, the sensor
resistance will change. This will result in a different
input voltage to the PCM. For more information, re-
fer to Group 14, Fuel System.
This sensor is installed in the intake manifold (Fig.
13, 4.0L engine or Fig. 14, 2.5L engine).
For component testing, refer to the Diagnostics/Ser-
vice Procedures section of this group.
For removal and installation of this component, re-
fer to the Component Removal/Installation section of
this group.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
The MAP sensor reacts to absolute pressure in the
intake manifold and provides an input voltage to the
Powertrain Control Module (PCM). As engine load
changes, manifold pressure varies, causing the MAP
Fig. 11 Ignition CoilÐTypical
Fig. 12 Coolant Temperature SensorÐTypical
Fig. 13 Air Temperature Sensor LocationÐ4.0L
Engine
Fig. 14 Air Temperature Sensor LocationÐ2.5L
Engine
JIGNITION SYSTEMS 8D - 5

sensor voltage to change. This change results in a
different input voltage to the PCM. The input volt-
age level supplies the PCM with information. This
relates to ambient barometric pressure during engine
start-up (cranking) and to engine load while the en-
gine is running. The PCM uses this input, along with
inputs from other sensors, to adjust air-fuel mixture.
For more information, refer to Group 14, Fuel Sys-
tem.
The MAP sensor is located in the engine compart-
ment near the rear of engine cylinder head (valve)
cover (Fig. 15). It is connected to the throttle body
with a vacuum hose and to the PCM electrically.
For component testing, refer to the Diagnostics/Ser-
vice Procedures section of this group.
For removal and installation of this component, re-
fer to the Component Removal/Installation section of
this group.
POWERTRAIN CONTROL MODULE (PCM)
The PCM was formerly referred to as the SBEC or
engine controller. On XJ models, the PCM is located
in the engine compartment next to the air cleaner
(Fig. 16). On YJ models, the PCM is located in the
engine compartment behind the windshield washer
fluid reservoir (Fig. 17).
The ignition system is controlled by the PCM.
Base ignition timing by rotation of distributor
is not adjustable.The PCM opens and closes the ig-
nition coil ground circuit to operate the ignition coil.
This is done to adjust ignition timing, both initial
(base) and advance, for changing engine operating
conditions.
The amount of electronic spark advance provided
by the PCM is determined by five input factors: En-
gine coolant temperature, engine rpm, intake mani-
fold air temperature, intake manifold absolute
pressure and throttle position.For removal and installation of this component, re-
fer to the Component Removal/Installation section of
this group.
For diagnostics, refer to the appropriate Powertrain
Diagnostic Procedures service manual for operation
of the DRB scan tool.
THROTTLE POSITION SENSOR
The sensor is mounted on the throttle body (Figs.
18 or 19). It is connected to the throttle blade shaft.
The sensor is a variable resistor. It provides the Pow-
ertrain Control Module (PCM) with an input signal
(voltage) that represents throttle blade position. As
the position of the throttle blade changes, the resis-
tance of the sensor changes.
The PCM supplies approximately 5 volts to the
sensor. The sensor output voltage (input signal to the
PCM) represents the throttle blade position. The
PCM receives an input signal voltage from the sen-
sor. This will vary in an approximate range of from 1
volt at minimum throttle opening (idle), to 4 volts at
wide open throttle. Along with inputs from other sen-
sors, the PCM uses the sensor input to determine
Fig. 15 MAP SensorÐTypical
Fig. 16 PCM LocationÐXJ Models
Fig. 17 PCM LocationÐYJ Models
8D - 6 IGNITION SYSTEMSJ

DIAGNOSTICS/SERVICE PROCEDURES
INDEX
page page
Automatic Shut Down (ASD) Relay............ 8
Camshaft Position Sensor Test............... 8
Crankshaft Position Sensor Test.............. 9
Distributor Cap........................... 9
Distributor Rotor......................... 10
DRB Scan Tool.......................... 10
Engine Coolant Temperature Sensor Test...... 12
General Information........................ 8
Ignition Coil............................. 11
Ignition Secondary Circuit Diagnosis.......... 12Ignition Timing........................... 14
Intake Manifold Air Temperature Sensor Test . . . 14
Manifold Absolute Pressure (MAP) Sensor Test . 14
On-Board Diagnostics (OBD)................ 19
Oxygen Sensor Tests..................... 19
Powertrain Control Module (PCM)............ 15
Spark Plug Secondary Cables............... 17
Spark Plugs............................ 16
Throttle Position Sensor Test............... 18
GENERAL INFORMATION
This section of the group, Diagnostics/Service Pro-
cedures, will discuss basic ignition system diagnos-
tics and service adjustments.
For system operation and component identification,
refer to the Component Identification/System Opera-
tion section of this group.
For removal or installation of ignition system com-
ponents, refer to the Component Removal/Installa-
tion section of this group.
For other useful information, refer to On-Board Di-
agnostics in the General Diagnosis sections of Group
14, Fuel System in this manual.
For operation of the DRB Scan Tool, refer to the
appropriate Powertrain Diagnostic Procedures ser-
vice manual.
AUTOMATIC SHUT DOWN (ASD) RELAY
Refer to RelaysÐOperation/Testing in the Group
14, Fuel System section of this service manual.
CAMSHAFT POSITION SENSOR TEST
The camshaft position sensor is located in the dis-
tributor on all engines.
To perform a complete test of this sensor and its
circuitry, refer to the DRB scan tool. Also refer to the
appropriate Powertrain Diagnostics Procedures man-
ual. To test the sensor only, refer to the following:
2.5L OR 4.0L ENGINE
For this test, an analog voltmeter is needed.Do
not remove the distributor connector from the dis-
tributor. Using small paper clips, insert them into
the backside of the distributor wire harness connec-
tor to make contact with the terminals. Be sure that
the connector is not damaged when inserting the pa-
per clips. Attach voltmeter leads to these paper clips.
(1) Connect the positive (+) voltmeter lead into
the sensor output wire. This is at done the distribu-
tor wire harness connector. For wire identification,
refer to Group 8W, Wiring Diagrams.(2) Connect the negative (-) voltmeter lead into the
ground wire. For wire identification, refer to Group
8W, Wiring Diagrams.
(3) Set the voltmeter to the 15 Volt DC scale.
(4) Remove distributor cap. Rotate (crank) engine
with starter until pulse ring (Fig. 1) enters the mag-
netic pickup on camshaft position sensor. Distributor
rotor should be pointed in 9 o'clock position. The
movable pulse ring should now be within the sensor
pickup.
(5) Turn ignition key to ON position. Voltmeter
should read approximately 5.0 volts.
(6) If voltage is not present, check the voltmeter
leads for a good connection.
(7) If voltage is still not present, check for voltage
at the supply wire. For wire identification, refer to
Group 8W, Wiring Diagrams.
Fig. 1 Pulse Ring/Rotor PositionÐTypical
8D - 8 IGNITION SYSTEMSJ

IGNITION COIL
To perform a complete test of the ignition coil and
its circuitry, refer to the DRB scan tool. Also refer to
the 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.
IGNITION COIL RESISTANCE
Fig. 9 Firing OrderÐ4.0L 6 Cylinder Engine
Fig. 10 Rotor InspectionÐTypical
Fig. 11 Ignition CoilÐTypical
JIGNITION SYSTEMS 8D - 11

ENGINE COOLANT TEMPERATURE SENSOR TEST
To perform a complete test of this sensor and its
circuitry, refer to the DRB scan tool. Also refer to the
appropriate Powertrain Diagnostics Procedures man-
ual. To test the sensor only, refer to the following:
The sensor is installed in the thermostat housing
(Fig. 12).
(1) Disconnect wire harness connector from sensor
(Fig. 12).
(2) Test the resistance of the sensor with a high in-
put impedance (digital) volt-ohmmeter. The resis-
tance should be less than 1340 ohms at normal
engine operating idle temperature. For resistance
values, refer to the Sensor Resistance chart. Replace
the sensor if it is not within the range of resistance
specified in the chart.
(3) Test continuity of the wire harness. This is
done between Powertrain Control Module (PCM)
wire harness connector terminal-2 and the sensor
connector terminal. Also check continuity between
wire harness terminal-4 to the sensor connector ter-
minal. Repair the wire harness if an open circuit is
indicated.
IGNITION SECONDARY CIRCUIT DIAGNOSIS
CHECKING FOR SPARK
CAUTION: When disconnecting a high voltage cable
from a spark plug or from the distributor cap, twist
the 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.
(1) Disconnect the ignition coil secondary cable
from center tower of the distributor cap. Hold the ca-
ble terminal approximately 12 mm (1/2 in.) from a
good engine ground (Fig. 13).WARNING: BE VERY CAREFUL WHEN THE ENGINE
IS CRANKING. DO NOT PUT YOUR HANDS NEAR
THE PULLEYS, BELTS OR THE FAN. DO NOT
WEAR LOOSE FITTING CLOTHING.
(2) Rotate (crank) the engine with the starter mo-
tor and observe the cable terminal for a steady arc. If
steady arcing does not occur, inspect the secondary
coil cable. Refer to Spark Plug Cables in this group.
Also inspect the distributor cap and rotor for cracks
or burn marks. Repair as necessary. If steady arcing
occurs, connect ignition coil cable to the distributor
cap.
(3) Remove a cable from one spark plug.
Fig. 12 Coolant Temperature SensorÐTypical
SENSOR RESISTANCE (OHMS)
Fig. 13 Checking for SparkÐTypical
8D - 12 IGNITION SYSTEMSJ

(4) Using insulated pliers, hold the cable terminal
approximately 12 mm (1/2 in.) from the engine cylin-
der head or block while rotating the engine with the
starter motor. Observe the spark plug cable terminal
for an arc. If steady arcing occurs, it can be expected
that the ignition secondary system is operating cor-
rectly. If steady arcing occurs at the spark plug ca-
bles, but the engine will not start, connect the DRB
scan tool. Refer to the Powertrain Diagnostic Proce-
dures service manual for DRB operation.
FAILURE TO START TEST
To prevent unnecessary diagnostic time and wrong
test results, the previous Checking For Spark test
should be performed prior to this test.
WARNING: SET PARKING BRAKE OR BLOCK THE
DRIVE WHEELS BEFORE PROCEEDING WITH THIS
TEST.
(1) Unplug the ignition coil harness connector at
the coil (Fig. 14).
(2) Connect a set of small jumper wires (18 gauge
or smaller) between the ignition coil and coil electri-
cal connector (Fig. 15).
(3) Determine that sufficient battery voltage (12.4
volts) is present for the starting and ignition sys-
tems.
(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 shut down relay.
²If voltage is at 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 near battery voltage during
the entire 5 seconds, turn the key off. Remove the60-way connector (Fig. 16) 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 17.
Using the jumper,momentarilyground terminal-19
of the 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.
Fig. 14 Coil Harness ConnectorÐTypical
Fig. 15 Coil TerminalsÐTypical
Fig. 16 PCM 60-Way Connector
Fig. 17 Special Jumper Ground-to-Coil Negative
Terminal
JIGNITION SYSTEMS 8D - 13

(10) If spark is not produced, replace the ignition
coil.
IGNITION TIMING
Base (initial) ignition timing is NOT adjustable
on any of the 2.5L 4 cylinder or 4.0L 6 cylinder
engines. Do not attempt to adjust ignition timing
by rotating the distributor.
Do not attempt to modify the distributor hous-
ing to get distributor rotation. Distributor posi-
tion 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
operation of the DRB Scan Tool.
INTAKE MANIFOLD AIR TEMPERATURE SENSOR
TEST
To perform a complete test of this sensor and its
circuitry, refer to the DRB scan tool. Also refer to the
appropriate Powertrain Diagnostics Procedures man-
ual. To test the sensor only, refer to the following:
(1) Disconnect the wire harness connector from the
sensor (Figs. 18 or 19).
(2) Test the resistance of the sensor with a input
impedance (digital) volt-ohmmeter. Do not remove
the sensor from the engine for testing. For resistance
values, refer to the Sensor Resistance chart. Replace
the sensor if it is not within the range of resistance
specified in the chart.
(3) Test the resistance of the wire harness. This is
done between the Powertrain Control Module (PCM)
wire harness connector terminal-21 and the sensor
connector terminal. Also check continuity between
terminal-4 to the sensor connector terminal. Repair
the wire harness as necessary if the resistance is
greater than 1 ohm.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
TEST
To perform a complete test of this sensor and its
circuitry, refer to the DRB scan tool. Also refer to the
appropriate Powertrain Diagnostics Procedures man-
ual. To test the sensor only, refer to the following:
The MAP sensor is located on the cowl panel near
the rear of the engine cylinder head (valve) cover
(Fig. 20).
(1) Inspect the sensor vacuum hose connections at
the throttle body and sensor (Fig. 20). Repair as nec-
essary.
CAUTION: When testing the sensor, be sure that
the harness wires are not damaged by the test
meter probes.Fig. 18 Air Temperature SensorÐ2.5L Engine
Fig. 19 Air Temperature SensorÐ4.0L Engine
SENSOR RESISTANCE (OHMS)
8D - 14 IGNITION SYSTEMSJ