Jeep XJ. Manual — part 632
Symptom:
*CHECKING THE ENGINE MECHANICAL SYSTEMS
POSSIBLE CAUSES
CHECKING ENGINE MECHANICAL SYSTEMS
TEST
ACTION
APPLICABILITY
1
NOTE: The following items should be checked as a possible cause of a
Driveability or No-Start problem.
Engine Valve Timing - must be within specification
Engine Compression - must be within specifications
Camshaft Lobes - check for abnormal wear
Engine Speed Sensor Pick-Up - check the flywheel slots for debris and deterioration
Engine Exhaust System - must be free of any restriction
Engine Drive Sprocket - must be properly positioned
Power Brake Booster - must be free of any vacuum leaks
Fuel - must be free of contamination
Fuel Injector - must not be plugged or restricted
Fuel Injection Pump - must be properly timed
NOTE: Check for any Technical Service Bulletins that may relate to the
problem.
Are there any problems evident?
All
Yes
→
Repair as necessary.
Perform ROAD TEST VERIFICATION - VER-2.
No
→
Test Complete.
180
DRIVEABILITY - DIESEL
Symptom:
*CHECKING THE FUEL COMPUTER
POSSIBLE CAUSES
ECM - FUEL COMPUTER OUTPUT CIRCUIT
FUEL COMP OUPUT CIRCUIT SHORTED TO VOLTAGE
FUEL COMPUTER OUTPUT CIRCUIT OPEN
FUEL COMPUTER OUTPUT CIRCUIT SHORT TO GROUND
OVERHEAD CONSOLE
PCM
PCM - FUEL COMPUTER OUTPUT CIRCUIT
TEST
ACTION
APPLICABILITY
1
Turn the ignition off.
Disconnect the ECM harness connectors.
Turn the ignition on.
Measure the voltage of the Fuel Computer Output circuit at the ECM harness
connector.
Is the voltage between 4.5 and 5.5 volts?
All
Yes
→
Below 4.5 volts
Above 5.5 volts
Repair the Fuel Computer Output circuit for a short to voltage.
Perform ROAD TEST VERIFICATION - VER-2.
2
Turn the ignition off.
Disconnect the ECM harness connectors.
Turn the ignition on.
Connect a jumper wire between ground and ECM harness connector C1 cavity 18
while observing the Overhead Fuel Computer.
Did the Overhead Fuel Computer status change?
All
Yes
→
Replace the ECM in accordance with the Service Information.
Perform ROAD TEST VERIFICATION - VER-2.
No
→
3
Turn the ignition off.
Disconnect the ECM harness connectors.
Turn the ignition on.
Connect one end of a jumper wire to ECM harness connector C1 cavity 18 while
observing the Overhead Fuel Computer.
With the DRB, select Body System and monitor PCI Bus Info while connecting and
disconnecting the other end of the jumper wire to ground.
Does the DRB display a change in Fuel Computer Status?
All
Yes
→
Replace the Overhead Console in accordance with the Service
Information.
Perform ROAD TEST VERIFICATION - VER-2.
No
→
Test Complete.
181
DRIVEABILITY - DIESEL
TEST
ACTION
APPLICABILITY
4
Turn the ignition off.
Disconnect the PCM and ECM harness connectors.
Measure the resistance of the Fuel Computer Output circuit between the ECM and
PCM harness connectors.
Is the resistance below 10.0 ohms?
All
Yes
→
No
→
Repair the Fuel Computer Output circuit for an open.
Perform ROAD TEST VERIFICATION - VER-2.
5
Turn the ignition off.
Disconnect the PCM and ECM harness connectors.
Measure the resistance between ground and the Fuel Computer Output circuit.
Is the resistance below 100.0 ohms?
All
Yes
→
Repair the Fuel Computer Output circuit for a short to ground.
Perform ROAD TEST VERIFICATION - VER-2.
No
→
Replace the PCM in accordance with the Service Information.
Perform ROAD TEST VERIFICATION - VER-2.
182
DRIVEABILITY - DIESEL
*CHECKING THE FUEL COMPUTER —
Continued
Symptom:
*CHECKING THE FUEL HEATER OPERATION
POSSIBLE CAUSES
FUEL HEATER RELAY
FUEL HEATER RELAY OUTPUT CIRCUIT OPEN
FUEL HEATER RESISTANCE
FUSED B+ CIRCUIT OPEN
GROUND CIRCUIT OPEN
IGNITION SWITCH OUTPUT CIRCUIT OPEN
RELAY GROUND CIRCUIT OPEN
TEST
ACTION
APPLICABILITY
1
Turn the ignition off.
Disconnect the Fuel Heater harness connector.
Turn the ignition on.
Using a 12-volt test light connected to ground, check the Fuel Heater Relay Output
circuit at the Fuel Heater harness connector.
Is the test light on?
All
Yes
→
No
→
2
Turn the ignition off.
Disconnect the Fuel Heater harness connector.
Turn the ignition on.
Using a 12-volt test light connected to 12-volts, check the Ground circuit at the Fuel
Heater harness connector.
Is the test light on?
All
Yes
→
No
→
Repair the Ground circuit for an open.
Perform ROAD TEST VERIFICATION - VER-2.
3
Turn the ignition off.
Disconnect the Fuel Heater harness connector.
Turn the ignition on.
With the DRB, read the Fuel Temperature Sensor.
NOTE: The Fuel temperature must be below 4.5°C (40°F).
Measure the resistance of the Fuel Heater.
Is the resistance between 0.7 and 2.0 ohms?
All
Yes
→
Test Complete.
No
→
Replace the Fuel Heater.
Perform ROAD TEST VERIFICATION - VER-2.
183
DRIVEABILITY - DIESEL
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