Fuel - Pump Related Driveability/Whine, DTC 32 or 44

GMC NUMBER:
92-6C-107

GROUP:
6C Engine Fuel

DATE:
July 1992

CORPORATE NUMBER:
276103



SUBJECT:
FUEL PUMP RELATED DRIVEABILITY ISSUE (DIAGNOSTIC INFORMATION)

MODELS:
1987-92 C/K, S/T TRUCKS AND M/L VANS



CONDITION
Customer may comment of fuel pump noise/whine and/or cold start stall; engine hesitation, sag, loss of power; or check engine light with codes 32 or 44. Condition(s) may be intermittent, but would typically be experienced in the first 5 minutes of engine/vehicle operation.

CAUSE
Possible fuel starvation.





The matrix in Figure 1 is provided to help during diagnosis activities.

Diagnostic Aids:

1. Oxygen sensor reading biased toward lean when the engine is under load.

2. Fuel pressure drops or does not increase by at least 5 psi when throttle moves from idle to part throttle.

3. Fuel integrator values steadily increasing under load.

4. Intermittent condition temporarily eased when accelerator pedal is released. Condition returns when accelerator pedal is reapplied.

5. Complete loss of fuel pressure.



CORRECTION
Use Section 6E3 of the appropriate service manual to diagnose possible fuel system related problems. The vehicle may need to be operated under a load while monitoring fuel pressure to detect the problem.

Important

MAKE CERTAIN THE FUEL SYSTEM IS PERFORMING TO SPECIFICATIONS BEFORE OTHER ENGINE CONTROL SYSTEM COMPONENTS ARE SERVICED.

SERVICE PROCEDURE
Follow procedures identified in the appropriate service manual. For electrical intermittents, see GMC Truck Service Bulletins 92-8A-09 issued September 1991 and 88-T-76 issued February 1988, as well as Section 8A of the service manual and instruction in required tool J-38125 usage.