TACHOMETER CALIBRATION PINS REPLACED BY WIRES

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 FLYWHEEL TEETH MOVEMENT 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 OCCURRING, ON MAY 2, 1988, A CHANGE WAS INCORPORATED IN PRODUCTION ON C6 AND C7 VEHICLES EQUIPPED WITH DIESEL ENGINES. EFFECTIVE WITH THE VEHICLE IDENTIFI- CATION 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 OP: N4500 LABOR TIME: .6 HR.

COPYRIGHT 1988 GMC TRUCK DIVISION, GENERAL MOTORS CORPORATION. ALL RIGHTS RESERVED.

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.