NO TRANS DOWN SHIFT AND/OR 80-85% THROTTLE

Subject: NO TRANSMISSION DOWNSHIFT AND/OR 80-85% THROTTLE

Model and Year: 1991-92 S/T TRUCKS WITH 4.3L ENGINE AND AUTOMATIC TRANSMISSION

THIS BULLETIN CANCELS AND SUPERSEDES DEALER SERVICE BULLETIN NO. 92-84-7A DATED FEBRUARY, 1992. THE VIN BREAKPOINTS HAVE BEEN REVISED. ALL COPIES OF 92-84-7A SHOULD BE DISCARDED.

Owners of some 1991 and 1992 S/T vehicles equipped with an automatic transmission and a 4.3L (LB4) engine may comment that their vehicle exhibits some of the following symptoms:

- Poor performance - Lack of power - Sluggishness - No downshift

IMPORTANT: THE SYMPTOMS FEEL LIKE TRANSMISSION FAILURE (LACK OF RESPONSE) BUT TRANSMISSION REPLACEMENT IS NOT NECESSARY.

These symptoms may be due to the accelerator cable being too long and/or the accelerator pedal having incorrect geometry. When one or both of these conditions are present, full throttle is not achieved. To correct this condition, replacement of accelerator pedal and/or cable with revised units is necessary for the 4.3L (LB4) engine.

VEHICLES INVOLVED

Involved are certain S/T vehicles with 4.3L (LB4) engines and automatic transmissions built before the following VIN Breakpoints:

FOR THE ACCELERATOR CABLE

MODEL YEAR PLANT FROM TO ---------- ----- ---- -- 1991-92 Pontiac S0P91 1GNCS18Z7N0110865 1991-92 Shreveport S0P91 1GCCS19ZXN8127815 1991-92 Moraine S0P91 1GCCS19Z7N2122624

FOR THE PEDAL/LEVER ASSEMBLY

MODELYEAR PLANT FROM TO --------- ----- ---- -- 1991-92 Pontiac S0P91 1GNCS18Z4N0119040 1991-92 Shreveport S0P91 1GCCS14Z0N8144551 1991-92 Moraine S0P91 1GNDT13Z0N2121994

SERVICE PROCEDURE:

1. Before replacing the accelerator cable and/or pedal assembly, connect TECH 1 or similar testing device to get a throttle position sensor (TPS) voltage reading. TPS voltage at idle should be less than 1.0 volts (approximately 0.6 volts). With the engine off and the accelerator pedal depressed to wide open throttle, the TPS voltage should read about 4.6 volts for the 4.3L (LB4) engine.

When the accelerator pedal is depressed and voltage readings are less than the previously mentioned voltage specifications, replace the pedal assembly with a redesigned pedal assembly (P/N 15679725).

Important: Make sure during pedal assembly installation that the insulation mat does not get trapped between the pedal assembly and dash panel (Figure 1).

Refer to the 1992 Light Duty Truck Service Manual, Fuel and Emissions Section, for proper accelerator pedal removal and installation.

2. Retest the TPS voltage. If the voltage readings for 4.3L (LB4) vehicles are still below the specified voltages, replace the accelerator cable with a redesigned cable (P/N 15693481).

Refer to 1992 Light Duty Truck Service Manual, Fuel and Emissions Section, for proper accelerator cable removal and installation.

SERVICE PARTS INFORMATION

Part Number Description Application Quantity ----------- ----------- ----------- -------- 15693481 Accelerator Control Cable S/T 1 (LB4 engine) 15679725 Accelerator Pedal Lever Asm. S/T 1

Parts are currently available from GMSPO.

WARRANTY INFORMATION

For vehicles repaired under warranty use:

Description Labor Operation ----------- --------------- Pedal, Accelerator - Replace J5350

Cable, Accelerator Control J5330 (Pedal to Lever) - Replace

Use applicable labor time guide to labor hours.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.