SURGE WHEN TCC ENGAGES NEW PROM P/N TO REVISE TCC

VEHICLES AFFECTED: 1985-86 "A" CARS WITH LR8 2.5L L4 ENGINES (VIN CODE R) 1985-86 "N" CARS WITH L68 2.5L L4 ENGINES (VIN CODE U)

Customer comments of "chuggle" or "surge" may be received on 1985-86 "A" and "N" cars with 2.5L L4 engines when the torque converter clutch (TCC) engages at lower vehicle sp'eeds.

This condition will be improved by the installation of a new service PROM. These service PROMS contain calibration changes designed to enhance vehicle driveability. The TCC engagement speed will be raised to 78 kph (49 MPH). Service PROM applications are listed below:

PROM P/N APPLICATION

1228020 1985 "A" WITH 2.84 AXLE 1227924 1985 "A" WITH 2.39 AXLE

1228021 1985 "N" WITH 2.84 AXLE 1228019 1986 "A" WITH 2.84 AXLE

1228018 1986 "A" WITH 2.39 AXLE 1228017 1986 "N" WITH 2.84 AXLE

*A check engine light with code 13 maybe experienced when PROM 1228021 is installed ina 1985 "N" car with 2.5L engine (sold in Canada). This engine used a non-closed loop Canadian emission system and did not have an oxygen sensor. PROM 1228021 is for a closed loop U.S. emission system which used an oxygen sensor. A unique Canadian PROM was never developed to raise the TCC engagement speed. Therefore, if PROM 1228021 is used to improve the driveability of a customer's vehicle, oxygen sensor P/N 8990741 should be installed to repair the code 13 condition. The oxygen sensor should be connected to the system using the existing connector and purple wire in the engine wiring harness.

Use applicable Labour Time and Operation Numbers.

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.