TACHOMETER CALIBRATION PINS REPLACED BY WIRES

SUBJECT: INACCURATE TACHOMETERS

MODELS: 1983-88 C6 AND C7 TRUCKS EQUIPPED WITH 8.2L DIESEL ENGINES (VIN CODES F AND G) AND TACHOMETERS (U16)

Medium duty vehicles equipped with diesel engines incorporate an electric tachometer which operates from a magnetic pickup. The pickup, located in the engine bell housing, senses the movement of the flywheel teeth to determine engine RPM. To calibrate the tachometer for the various engine flywheels, a pin is inserted in the back of the tachometer (refer to Figures 1 and 2). An improper, loose or missing calibration pin will cause tachometer inaccuracy.

To reduce the potential of these conditions occur- ring, on May 2, 1988, a change was incorporated in production on C6 and C7 vehicles equipped with diesel engines. Effective with the vehicle identification numbers listed below, tachometer pins were replaced by a soldered "jumper" wire:

GMC: 1GBL7D1B9JV529396 Chevrolet: 1GBJ6T1B0JV115852

In the event tachometer failure occurs as the result of calibration pin failure, it can be repaired by having an authorized Delco Electronics Mechanical Speedometer/Tachometer Service Center perform the above change.

For repairs to the vehicle under warranty use: Labor Operation: N4500 Labor Time: .6 Hr.

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.