Fuel Pump - Diagnosis

NO: 14-06-97

GROUP: Fuel

DATE: Jul. 3, 1997

SUBJECT:
Fuel Pump Diagnosis

MODELS:
1997 (TJ) Wrangler
1996 (ZJ) Grand Cherokee
1996 (ZG) Grand Cherokee - International Markets
1994 - 1996 (XJ) Cherokee

SYMPTOM/CONDITION:

Symptoms may include no start, rough idle, long crank times, driveway die outs or erratic fuel pressure. A new fuel pump has been released which delivers improved performance. This pump should be used whenever fuel pump failures are encountered.

DIAGNOSIS:

Basic fuel system diagnostics should be used as outlined in the appropriate service manual. A brief recap of the basic diagnostics follows:

Fuel pressure specification - 49 psi - plus or minus 5 psi.

High fuel pressure indicates problems with the fuel pressure regulator. Refer to the service manual for regulator diagnosis. Do not replace the fuel pump for high pressure.

Low fuel pressure - Low pressure could indicate a pump problem or it could indicate a plugged fuel filter or restricted fuel line or no fuel in the tank. Be sure to check these items before replacing the fuel pump.

Fuel System Leak down - When checking fuel pressure be sure to check the integrity of the system after shut down. With the fuel pressure gauge connected, shut the engine off and observe the pressure gauge. The system should maintain at least 24 psi for five minutes after shut down. If the pressure bleeds off quicker, it could indicate that an injector is leaking down or that the pressure regulator is leaking. This can lead to driveablity problems and require further diagnosis.

NOTE:
IN RARE CASES WHERE MULTIPLE FUEL PUMP FAILURES HAVE OCCURRED ON THE SAME VEHICLE, A BUILD UP OF RESIDUE MAY HAVE ACCUMULATED ON THE INSIDE OF THE FUEL TANK. THE PRESENCE OF THIS RESIDUE IS NOT EASILY IDENTIFIABLE. THE RESIDUE CAN PASS THROUGH THE IN TANK FILTER AND CONTAMINATED THE PUMP ROTOR. IF MULTIPLE FAILURES HAVE OCCURRED WITH NO OBVIOUS INDICATION OF THE CAUSE, CONSIDERATION SHOULD BE MADE TO REPLACING THE FUEL TANK TO AVOID FUTURE PROBLEMS.

PARTS REQUIRED:

1 04762964 Pump Module - 1994-1995 XJ
1 04798941 Pump Module - 1996 XJ
1 04883261 Pump Module - 1996 ZJ
1 04897754AB Pump Module - 1997 TJ - 15 gallon tank
1 04897755AB Pump Module - 1997 TJ - 19 gallon tank

POLICY: Information Only