POSSIBLE BURNT S/P TIPS DETONATION INDUCED PREIGNITION

Model and Year: 1984-85 CAPRICE/INPALA WITH 5.0L (VIN CODE H) OR 5.7L (VIN CODE 6)

TO: ALL CHEVROLET DEALERS

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

Spark plug gap should be set at .035".

Use applicable labor 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.