DETONATION-SPARK KNOCK (UPDATE OR INSTALL NEW ESC)

SUBJECT: DRIVEABILITY IMPROVEMENTS - NEW PROM AND ESC MODULE CALIBRATION

MODELS/YEARS: 1991-92 CUSTOM CRUISER WITH 5.0L (VIN E) OR 5.7L (VIN 7) ENGINE

This bulletin Supersedes 91-T-129 which should be discarded. This bulletin contains additional information as well as additional model years for spark knock/detonation comments.

CONDITION: Some owners of 1991 Custom Cruisers with the 5.0L (VIN E) engine may comment about low speed driveability. In addition, some owners may comment about tip-in hesitation, sags, backfire, spark knock/detonation or long "crank times" on cold start. Also, some owners of 1992 models with the 5.0L (VIN E) and 5.7 (VIN 7) engines may comment about spark knock/detonation.

CORRECTION: Make sure the engine control system is operating properly and if nothing is found wrong, it may be necessary to replace the PROM and ESC module listed below. The PROM and ESC module calibrations have been updated to address these comments. The PROMs listed for the 1991 5.0L are for all the conditions mentioned above. The 5.0L ESC module and 5.7L PROM are for detonation/spark knock only.

EMISSION PART PART SCANNER BROADCAST APPLICATION SYSTEM NUMBER NAME I.D. I.D. ----------- -------- ------ ---- ------- --------- 1991/5.0L FEDERAL 16164612 PROM 4611 AYDM 1991/5.0L CALIFORNIA 16165912 PROM 5941 AYMJ 1991-92/5.0L NATIONAL 16175099 ESC MODULE 1992/5.7L NATIONAL 16175898 PROM 5901 BATJ

Parts are currently be available from GMSPO.

WARRANTY INFORMATION:

Labor Operation: T0500 Labor Time: 0.5 hours

Use applicable labor operation and time from the labor time guide for ESC module replacement.

Trouble Code: 92

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.