DETONATION/EXHAUST ODOR INSTALL NEW PROM

SUBJECT: DETONATION AND/OR EXHAUST ODOUR (INSTALL NEW PROM)

VEHICLES AFFECTED: 1990 C/K, R/V, G, P AND V TRUCK W/7.4L (ABOVE 8600 GVW)

Condition:

---------- Some owners of 1990 trucks with the 7.4L engine may comment of either detonation at highway speeds or exhaust odour (sulfur smell) at idle.

Cause:

------- The original spark advance and idle calibration may generate detonation or sulfur odour comments for a few isolated conditions.

Correction:

----------- On trucks where these conditions can not be repaired using normal service procedures, a revised calibration PROM should be installed (See below).

Part Emission PROM SCANNER Number System Trans. Broadcast I.D. ----------- ------------ ---------- ---------- ------ 16165446 NA4 (above M40 (Auto) AYKK 5451 8600 GVW)

16165447 NA4 (above M20 (Manual) AYKL 5461 8600 GVW)

Note: These PROMs SHOULD NOT BE USED on the Chevy "S.S."

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.