DETONATION/EXHAUST ODOR INSTALL NEW PROM

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

MODELS: 1990 C/K, R/V, G, and P TRUCKS WITH 7.4L ENGINES (ABOVE 8600 GVW)

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

Cause: The original spark advance and idle calibration may generate detonation or sulfur odor 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).

PROM Part Number Emission System Trans. Broadcast Scanner ID ----------- --------------- --------- --------- ----------- 16165446 NA4 (above 8600 GVW) M40(Auto) AYKK 5451 16165447 NA4 (above 8600 GVW) M20(Manual) AYKL 5461

Labor Operation Number: T0500 Labor Time: .6 Hour

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.