ENGINE DETONATION INSTALL NEW PROM PKG.

SUBJECT: ENGINE DETONATION - INSTALL NEW PROM PACKAGE

MODELS/YEARS: 1990-91 CUTLASS CALAIS WITH AUTOMATIC TRANSAXLE AND 2.5L (VIN U) ENGINE

This bulletin cancels and replaces Dealer Technical Bulletin 91-T-192 which should be discarded.

CONDITION: Some owners of 1990-91 Cutlass Calais may comment about more than normal engine detonation. This level of detonation is more than the burst detonation that is inherent with the 2.5L (VIN U) engine at off-idle tip-in at elevated coolant temperatures. Detonation may occur as steady state deto- nation, detonation on a slight grade or detonation on a light acceleration. Prior attempts to correct this detonation may include the use of top engine cleaners, decarboning or installation of a new head gasket. However, the detonation will return in a short amount of mileage.

CAUSE: The octane requirement of the engine increases with mileage. Therefore, original spark calibration may produce detonation in some vehicles.

CORRECTION: The correction for this condition is a new PROM package. This PROM will modify the spark tables and raise the Torque Converter Clutch (TCC) engagement point to 44 MPH. THE CUSTOMER SHOULD ALSO BE ADVISED THAT THIS PROM MAY HAVE A NEGATIVE IMPACT ON FUEL ECONOMY.

Note: Dealer Technical Bulletin 90-T-196 is still effective for a chuggle only condition.

1990 1991 The new PROM Package P/N is: 16168732 16176078 Broadcast Code: AZBH BATT ScannerID: 8791 6081

Parts are currently available from GMSPO.

WARRANTY INFORMATION:

Labor Operation: T0500 Labor Time: 0.3 Hour 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.