POOR PERFORMANCE LOADED COND. SPARK PLUG CHANGE

Model and Year: 1984-85 "C-K-G" 10-30 TRUCKS WITH FEDERAL EMISSIONS AND LE9 (305 VIN CODE H), LF3 (305 VIN CODE F) AND LS9 (350 VIN CODE L)

TO: ALL CHEVROLET DEALERS

This revised Dealer Bulletin cancels and replaces 85-169 dated December 1985 which should be destroyed. This reissue reflects additional engine applications.

Some 1984-85 vehicles equipped with subject V8 engines may experience induced pre-ignition or poor performance when operating in a loaded condition or pulling a grade. As a result of the pre-ignition, the ESC retards the spark timing, and a noticeable reduction in performance may occur. In the event the pre-ignition condition is not corrected by the ESC spark retard, continued operation under these conditions could result in internal engine damage. To reduce the possibility of this occurrence, the spark plugs should be changed to a colder heat range.

When these conditions exist, the original equipment (R45TS) spark plugs should be replaced with R43CTS (P/N 5613810). The correct spark plug gap is .045".

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.