POSSIBLE BURNT S/P TIPS DETONATION INDUCED PREIGNITION

VEHICLES AFFECTED: 1984-85 'B' Models With 5.0L (LG4) or 5.7L (LM1) Engines

Customer comments may be received regarding detonation induced pre-ignition on 1984-85 'B' models with 5.0L LG4 or 5.7L LM1 engines. Detonation is most likely to occur when the vehicle is pulling on a grade or in extended periods of heavy load operation and may lead to pre-ignition which can be recognized by melted spark plug centre wire.

If normal diagnostic procedures do not correct the cause of the detonation, the original spark plugs (R45TS) should be replaced with R43CTS plugs, P/N 5613810. These plugs have a colder heat range but are equipped with a copper core to improve plug fouling.

Spark plug gap should be set at .89mm (.035 in.).

Use applicable labour time and operation number.

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.