INACCURATE ELECT. TACHOMETER (DIAGNOSIS & PROCEDURE)

MEDIUM DUTY VEHICLES WITH DIESEL ENGINES INCORPORATE AN ELECTRIC TACHOMETER WHICH IS DRIVEN FROM A MAGNETIC PICKUP. THE 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 TRANSMISSION: 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.