BACKFIRE ON ACCELERATION (CORRECT CALIBRATION). GMC Truck Jimmy

SUBJECT: BACKFIRE ON ACCELERATION (CORRECT CALIBRATION)

MODELS: 1994 CHEVROLET AND GMC TRUCK S/T MODELS WITH 4.3L ENGINE (VIN Z - RPO LB4) AND MANUAL TRANSMISSION (RPO MY2)

CONDITION:

SOME OWNERS MAY EXPERIENCE A BACKFIRE CONDITION UPON ACCELERATION.

CAUSE:

INSUFFICIENT IGNITION TIMING ADVANCE IN THE SPARK CALIBRATION UNDER SOME DRIVING CONDITIONS.

CORRECTION:

MORE ROBUST CALIBRATIONS HAVE BEEN RELEASED TO ADDRESS THIS CONCERN. THIS CALIBRATION WILL NOT CORRECT ANY OTHER DRIVEABILITY CONCERN.

IMPORTANT: THESE SERVICE CALIBRATIONS SHOULD ONLY BE USED IF A BACKFIRE CONCERN STILL EXISTS IN A VEHICLE WHICH HAS HAD THE BASE TIMING CHECKED AND SET TO SPECIFICATION.

LAUNCH DETONATION MAY OCCUR IN VEHICLES SERVICED WITH THESE CALIBRATIONS; PARTICULARLY IN VEHICLES WHICH ARE HEAVILY LOADED OR TOWING TRAILERS.

SERVICE INFORMATION:

SERVICE "FLASH" CALIBRATIONS ARE AVAILABLE STARTING WITH THE DECEMBER, 1994 CD ROM.

CALIBRATION P/N USAGE 16206779 CALIFORNIA 16206780 FEDERAL

WARRANTY INFORMATION:

LABOR OPERATION: T0500 LABOR TIME: 0.6 HR.

FIGURES: 0 ATTACHMENTS: 0

GENERAL MOTORS BULLETINS ARE INTENDED FOR USE BY PROFESSIONAL TECHNICIANS, NOT A "DO-IT-YOURSELFER." THEY ARE WRITTEN TO INFORM THOSE TECHNICIANS OF CONDITIONS OCCURRING 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 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.