SUSTAINED DETONATION/KNOCK (APPLY STD DIAG. PROC./INST.. GMC Truck Safari

******************************************************************** THIS BULLETIN CANCELS AND SUPERSEDES CORPORATE BULLETIN 236511.

******************************************************************** REVISION 10/13/93

THIS BULLETIN IS BEING REVISED TO CORRECT THE SERVICE PROM KIT NUMBERS FOR THE FEDERAL C (BHSM) AND THE CALIFORNIA C (BHUT) CALIBRATIONS. PLEASE DISCARD PREVIOUS DIVISIONAL PUBLICATIONS:

CHEVROLET 92-285B-6E GMC TRUCK 92-6E-162 GM OF CANADA 93-6E-128 ********************************************************************

SUBJECT: SUSTAINED DETONATION/KNOCK (APPLY STANDARD DIAGNOSTIC PROCEDURE/INSTALL NEW PROM)

MODELS: 1992 C/K AND S/T TRUCKS, G AND M/L VANS

CONDITION:

SOME OWNERS OF 1992 S/T, C/K, M/L OR G TRUCKS EQUIPPED WITH 4.3L (LB4) V6 (VIN Z) ENGINES MAY COMMENT THAT THE ENGINE EXHIBITS SUSTAINED DETONATION (KNOCK) DURING ACCELERATION OR CLIMBING A GRADE. THE SUSTAINED DETONATION (KNOCK) OCCURS AFTER THE ENGINE REACHES NORMAL OPERATING TEMPERATURE. THE DETONATION MAY OCCUR AT PART THROTTLE OR WIDE OPEN THROTTLE OPERATION.

NOTE: SOME BURST DETONATION (KNOCK) DURING "TIP-IN" ACCELERATION AND/OR AT SHIFT POINTS IS CONSIDERED NORMAL.

CAUSE:

SOME ENGINES MAY HAVE HIGHER THAN INTENDED COMPRESSION RATIOS AFTER ACCUMULATING CARBON DEPOSITS.

CORRECTION:

FOLLOW STANDARD DETONATION DIAGNOSTIC PROCEDURES IN THE APPRO- PRIATE SERVICE MANUAL. IF THE CAUSE OF THE DETONATION CANNOT BE DETERMINED AND ELIMINATED AFTER STANDARD DIAGNOSTIC PROCE- DURES, THE CONDITION MAY BE CORRECTED BY THE INSTALLATION OF THE CORRECT FIELD FIX CALIBRATION PROM FROM THE TABLE BELOW:

NOTE: THE MANUAL TRANSMISSION CALIBRATIONS CONTAIN THE NEUTRAL GEAR RATTLE UPDATE (INCREASED IDLE SPEED). IF A VEHICLE IS EXPERIENCING NEUTRAL GEAR RATTLE, HARDWARE CHANGES AND THE NEW CALIBRATION ARE REQUIRED. FOR A DESCRIPTION OF NEUTRAL GEAR RATTLE AND THE REQUIRED HARDWARE CHANGES, SEE CORPORATE BULLETIN 267201.

NOTE: THE S/T SERIES AUTOMATIC TRANSMISSION CALIBRATIONS CONTAIN THE TORQUE CONVERTER CLUTCH (TCC) LOCK-UP UPDATE. FOR A DESCRIPTION OF THE TCC UPDATE, SEE CORPORATE BULLETIN 137107.

WARNING: USE OF A DETONATION FIELD FIX CALIBRATION PROM IN A NONDETONATING ENGINE MAY RESULT IN DEGRADED DRIVE- ABILITY. GENERAL MOTORS STRONGLY RECOMMENDS THE CONCERN BE PROPERLY IDENTIFIED AS SUSTAINED DETONATION OCCURRING AFTER THE ENGINE IS FULLY WARMED TO NORMAL OPERATING TEMPERATURE.

PROMS 1992 LB4 VIN Z TRANS AXLE EMISSION SERVICE B/C SCAN OLD B/C* PLATFORM RPO RPO CLASS PROM KIT CODE I.D. CODE -------- ----- ---- -------- -------- ---- ---- -------- S/T MY2 GU2 NA5/NA6/NB2 16196188 BHWN 6235 AULR/BHSF S/T MY2 GU4 NA5/NA6/NB2 16196192 BHWP 6245 AULS/BHSH S/T MY2 GU6 NA5/NA6/NB2 16196199 BHWR 6255 AULT/BHSJ S/T MD8 ALL NA5/NA6 16192257 BFNF 2295 BARL/AWHH S/T MD8 ALL NB2 16192260 BFNH 2305 BARM/AWHF

C1,C2/K1,K2 MT8 ALL NA5/NA6+NA1 16196134 BHSN 6205 BCZP/AULJ K1,K2 MG5 ALL NA5/NA6+NA1 16196134 BHSN 6205 BCZP/AZUS C1,C2/K1,K2 MT8 ALL NB2+NA1 16196153 BHUU 6225 BCZR/AULM K1,K2 MG5 ALL NB2+NA1 16196153 BHUU 6225 BCZR/AZUT C1,C2 MG5 ALL NA5/NA6 16196131 BHSM 6195 BDCW/AULH C1,C2 MG5 ALL NB2+NA1 16196152 BHUT 6215 BDCX/AULL C1,C2/K1,K2 MD8 ALL NA5/NA6 16192249 BFNC 2275 AULF C1,C2/K1,K2 MD8 ALL NB2 16192253 BFND 2285 AULK

G1,G2,G3/M1 MD8 ALL NA5/NA6 16196101 BHSA 6105 AULN/BCKU G1,G2,G3/M1 MD8 ALL NB2 16196108 BHSC 6125 AULP/BCKT

L1 MD8 ALL NA5/NA6 16196104 BHSB 6115 AYAW/BCNU L1 MD8 ALL NB2 16196111 BHSD 6135 AYAX/BCNW

* OLD BROADCAST CODE IS INCLUDED TO HELP THE TECHNICIAN DETERMINE IF A PREVIOUS FIELD FIX HAS BEEN INSTALLED. IF A BROADCAST CODE OTHER THAN ONE APPEARING ON THIS LIST IS PRESENT, CONTACT MARKETING DIVISION TECHNICAL ASSISTANCE FOR INSTRUCTION.

PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

WARRANTY INFORMATION:

FOR VEHICLES REPAIRED UNDER WARRANTY: LABOR TIME (IN HOURS) LABOR OPERATION M L G C K S T --------------- --- --- --- --- --- --- --- T0500 - PROM REPLACE 0.6 0.6 0.6 0.6 0.6 0.6 0.6

FIGURES: 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 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.