NO DOWNSHIFT AT 80% THROTTLE INSTALL REV. CABLE/PEDAL ASSY.

SUBJECT: NO TRANSMISSION DOWNSHIFT AND/OR 80-850/o THROTTLE (INSTALL REVISED ACCELERATOR CABLE AND/OR PEDAL ASSEMBLY)

MODELS: 1991-1992 S/T WITH 4.3L ENGINE, AUTOMATIC TRANSMISSION

THIS BULLETIN CANCELS AND REPLACES GMC TRUCK SERVICE BULLETIN 92-7A-44, DATED JANUARY 1992 TO CORRECT THE VIN BREAKPOINTS. ALL COPIES OF 92-7A-44 SHOULD BE DESTROYED.

GMC TRUCK RECOMMENDS THAT A COPY OF THIS BULLETIN ALSO BE FILED UNDER SECTION 6C-ENGINE FUEL.

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 TRANS- MISSION 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 Model Year Plant From TO ----- ----- ----- ---- -- GMC 1991-92 Pontiac SOP 91 1GKCS18Z0N0504057 GMC 1991-92 Shreveport SOP 91 1GCTS19Z1N8505990 GMC 1991-92 Moraine SOP 91 1GKDT13Z8N2506457

FOR THE PEDAL/LEVER ASSEMBLY

Model Model Year Plant From TO ----- ----- ----- ---- -- GMC 1991-92 Pontiac SOP 91 1GTCS19Z0N0506093 GMC 1991-92 Shreveport SOP 91 1GTDT19Z5N8509235 GMC 1991-92 Moraine SOP 91 1GTDT19ZXN2506480

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 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 Fuel and Emissions Service Manual X-9236, page 4-90, 4-91 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 Fuel and Emissions Service Manual X-9236, page 4-90 for proper accelerator cable removal and installation.

SERVICE PARTS INFORMATION

Part Number Description Application Qty. ------ ----------- ----------- ---- 15693481 Accelerator Control S/T 1 Cable (LB4 Engine)

15679725 Accelerator Pedal S/T 1 Lever Asm.

Parts are currently available from GMSPO.

WARRANTY INFORMATION

For vehicles repaired under warranty use:

Labor Labor Description Operation Time ----------- --------- ----- Pedal, Accelerator J5350 0.3 hrs. Replace

Cable, Accelerator Control J5330 0.4 hrs. (Pedal to Lever)-Replace

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.