INACCURATE ELECT. TACHOMETER (DIAGNOSIS & PROCEDURE)

Subject: TACHOMETER

Model and Year: MEDIUM DUTY TRUCKS WITH DIESEL ENGINES

TO: ALL CHEVROLET DEALERS

Medium Duty vehicles with diesel engines incorporate an electric tachometer which is driven from a magnetic pickup. This pickup is located on the bell housing and senses the number of flywheel teeth. To calibrate the tachometer for the various flywheels (transmissions), a pin is inserted in the rear of the tachometer, Figure No. 1. An incorrect pin will cause tachometer inaccuracy.

With white pin, P/N 5658631, installed (Figure No.2), the tachometer is calibrated for 8.2 engines with automatic transmissions, option MF1.

With orange pin, P/N 5658769, installed (Figure No. 3), the tachometer is calibrated for 8.2 engines with standard transmissions, all CAT engines, and automatic transmissions ME3 and ME5.

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.