A/T - No Transmission Downshift/80-85% Throttle

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GMC NUMBER: 92-7A-44(A)

GROUP: 7A Automatic Transmission

DATE: April, 1992

CORPORATE
NUMBER: 167106R


SUBJECT:
NO TRANSMISSION DOWNSHIFT AND/OR 80-85% 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-A4 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 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
Model Year Plant From To
GMC 1991-92 Pontiac SOP 91 1GKCS18ZON0504057
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