Jeep XJ. Manual — part 856
Symptom:
*CHECKING FUEL DELIVERY
POSSIBLE CAUSES
FUEL PUMP RELAY
FUEL PRESSURE OUT OF SPECS
RESTRICTED FUEL SUPPLY LINE
FUEL PUMP INLET STRAINER PLUGGED
FUEL PUMP MODULE
FUEL PUMP CAPACITY (VOLUME) OUT OF SPECS
FUEL PUMP RELAY FUSED B+ CIRCUIT
FUEL PUMP RELAY OUTPUT CIRCUIT OPEN
FUEL PUMP GROUND CIRCUIT OPEN/HIGH RESISTANCE
FUEL PUMP MODULE
TEST
ACTION
APPLICABILITY
1
Turn the ignition on.
With the DRBIII
t, actuate the ASD Fuel System test.
Note: It may be necessary to use a mechanics stethoscope in the next step.
Listen for fuel pump operation at the fuel tank.
Does the Fuel Pump operate?
All
Yes
→
No
→
Caution: Stop All Actuations.
2
Turn the ignition off.
WARNING: The fuel system is under a constant pressure even with the
engine off. Before testing or servicing any fuel system hose, fitting or line,
the fuel system pressure must be released.
Install a fuel pressure gauge to the fuel rail test port.
Turn the ignition on.
With the DRBIII
t, actuate the ASD Fuel System test and observe the fuel pressure
gauge.
NOTE: Fuel pressure specification is 339.2 KPa +/- 34 KPa (49.2 psi +/- 5 psi).
Choose a conclusion that best matches your fuel pressure reading.
All
Below Specification
Within Specification
Above Specification
Replace the fuel filter/fuel pressure regulator.
Perform POWERTRAIN VERIFICATION TEST VER - 1.
Caution: Stop All Actuations.
185
DRIVEABILITY - GAS
TEST
ACTION
APPLICABILITY
3
Turn the ignition off.
WARNING: The fuel system is under a constant pressure even with the
engine off. Before testing or servicing any fuel system hose, fitting or line,
the fuel system pressure must be released.
Raise vehicle on hoist, and disconnect the fuel pressure line at the fuel pump module.
Install special 5/16
9 fuel line adapter tool #6539 between disconnected fuel line and
the fuel pump module.
Attach a fuel pressure test gauge to the
9T9 fitting on tool #6539.
Turn the ignition on.
With the DRBIII
t, actuate the ASD Fuel System test and observe the fuel pressure
gauge.
NOTE: Fuel pressure specification is 339.2 KPa +/- 34 KPa (49.2 psi +/- 5 psi).
Is the fuel pressure within specification now?
All
Yes
→
Repair/replace fuel supply line as necessary.
Perform POWERTRAIN VERIFICATION TEST VER - 1.
No
→
Caution: Stop All Actuations.
4
Turn the ignition off.
WARNING: The fuel system is under a constant pressure even with the
engine off. Before testing or servicing any fuel system hose,fitting or line,
the fuel system pressure must be released.
Remove the Fuel Pump Module and inspect the Fuel Inlet Strainer.
Is the Fuel Inlet Strainer plugged?
All
Yes
→
Replace the Fuel Pump Inlet Strainer.
Perform POWERTRAIN VERIFICATION TEST VER - 1.
No
→
Replace the Fuel Pump.
Perform POWERTRAIN VERIFICATION TEST VER - 1.
5
Note: The fuel pressure must be within specification before continuing.
Turn the ignition off.
WARNING: The fuel system is under a constant pressure even with the
engine off. Before testing or servicing any fuel system hose, fitting or line,
the fuel system pressure must be released.
Disconnect the fuel supply line at the fuel rail.
Connect fuel line adapter #6539(5/16
9) or #6631(3/89) to the disconnected fuel supply
line. Insert the other end of the adapter into a graduated container.
Caution: Do not operate the fuel pump for more than 7 seconds in the next
step. Fuel pump module reservoir may run empty and damage to the fuel
pump will result.
Note: Specification: A good fuel pump will deliver at least 1/4 liter (1/2 pint)
of fuel in 7 seconds.
Turn the ignition on.
With the DRBIII
t, actuate the ASD Fuel System test for 7 seconds.
Is the fuel pump capacity within specification?
All
Yes
→
Test Complete.
No
→
Check for a kinked/damaged fuel supply line between the fuel
tank and fuel rail. If OK, replace the fuel pump module.
Perform POWERTRAIN VERIFICATION TEST VER - 1.
Caution: Stop All Actuations.
186
DRIVEABILITY - GAS
*CHECKING FUEL DELIVERY —
Continued
TEST
ACTION
APPLICABILITY
6
Turn the ignition off.
Disconnect the fuel pump module harness connector.
Turn the ignition on.
With the DRBIII
t, actuate the ASD Fuel System test.
Using a 12 volt test light connected to ground, probe the Fuel Pump Relay Output
circuit at the Fuel Pump Module harness connector.
Does the test light illuminate brightly?
All
Yes
→
No
→
Caution: Stop All Actuations.
7
Turn the ignition off.
Disconnect the Fuel Pump Module harness connector.
Note: Check connectors - It is critical that the connector is free from any
signs of corrosion or deformities - Clean/repair as necessary.
Using a test light connected to battery voltage, probe the Fuel Pump ground circuit
at the Fuel Pump Module harness connector.
Does the test light illuminate brightly?
All
Yes
→
No
→
Repair the open/high resistance in the fuel pump ground circuit.
Perform POWERTRAIN VERIFICATION TEST VER - 1.
8
If there are no possible causes remaining, view repair.
All
Repair
Replace the Fuel Pump Module.
Perform POWERTRAIN VERIFICATION TEST VER - 1.
9
Turn the ignition off.
Remove the Fuel Pump Relay from the PDC.
With a 12 volt test light connected to ground, probe the Fuel Pump Relay Fused B+
circuit at the PDC.
Does the test light illuminate?
All
Yes
→
No
→
Repair the Fuel Pump Realy Fused B+ circuit. Check for open
fuse in the PDC.
Perform POWERTRAIN VERIFICATION TEST VER - 1.
10
Turn the ignition off.
Remove the Fuel Pump Relay from the PDC.
Disconnect the Fuel Pump Module harness connector.
NOTE: Check connectors - It is critical that the connector is free from any
signs of corrosion or deformities
Measure the resistance of the Fuel Pump Relay Output circuit from the relay
connector to the fuel pump module connector.
Is the resistance below 5.0 ohms?
All
Yes
→
Replace the Fuel Pump Relay
Perform POWERTRAIN VERIFICATION TEST VER - 1.
No
→
Repair the Fuel Pump Relay Output circuit for an open.
Perform POWERTRAIN VERIFICATION TEST VER - 1.
187
DRIVEABILITY - GAS
*CHECKING FUEL DELIVERY —
Continued
Symptom:
*CHECKING IAC MOTOR
POSSIBLE CAUSES
IAC MOTOR OPERATION
IAC DRIVER CIRCUITS OPEN
IAC MOTOR
TEST
ACTION
APPLICABILITY
1
Turn the ignition on.
With the DRBIII
t, monitor engine RPM.
With the DRBIII
t, set the engine speed to 1400 RPM.
Does the engine speed reach 1400 rpm?
All
Yes
→
The IAC Motor is operation normally
Perform POWERTRAIN VERIFICATION TEST VER - 2.
No
→
2
Turn the ignition off.
Disconnect IAC Motor harness connector.
Disconnect the PCM harness connector.
Repeat each measurement for each IAC Driver circuit.
Measure the resistance of each IAC Driver circuit between the IAC Motor harness
connector and the PCM harness connector.
Is the resistance below 5.0 ohms at all IAC Driver circuits?
All
Yes
→
Replace the IAC Motor.
Perform POWERTRAIN VERIFICATION TEST VER - 2.
No
→
Repair the IAC Driver circuit(s) for an open.
Perform POWERTRAIN VERIFICATION TEST VER - 2.
188
DRIVEABILITY - GAS
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