POOR PERFORMANCE LOADED COND. SPARK PLUG CHANGE

MODELS: 1984-85 C, K, G TRUCKS EQUIPPED WITH THE LE9 5.0L, LF3 5.0L, OR LS9 5.7L ENGINE AND ELECTRIC SPARK CONTROL (ESC) FEDERAL EMISSIONS AND ELECTRONIC SPARK TIMING (EST) CALIFORNIA EMISSIONS.

THIS BULLETIN CANCELS AND SUPERSEDES 86-B-21 (DECEMBER,1985) ALL COPIES OF WHICH SHOULD BE DESTROYED.

Some 1984-85 vehicles equipped with the LE9 5.0L (VIN Code H), LF3 5.0L (VIN Code F), or LS9 5.7L (VIN Code L) engine may experience detonation (preignition) or poor performance when operating in a loaded condition or pulling a grade. As a result of the preignition, the ESC (Federal) or EST (Califomia) retards the spark timing, and a noticeable reduction in performance may occur. In the event the preignition condition is not corrected by the ESC/EST spark retard, continued operation under these conditions could result in intemal 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 (R44TS) spark plugs should be replaced with R43CTS (P/N 5613810). The correct spark plug gap is .045". Starting with 1986 vehicles, the LE9, LF3, LS9, and LT9 engines are built with the R43CTS spark plugs.

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.