SERVICE MANUAL UPDATE SEC.6E3- C2 DRIVEABILITY & EMISSIONS

SUBJECT: SERVICE MANUAL UPDATE/SECTION 6E3-C2 DRIVEABILITY/EMISSIONS - REVISED FUEL CUT-OFF SPECIFICATIONS

VEHICLES AFFECTED: 1990-91 'A/F/J/L/W' 3.1L, 3.4L

This bulletin revises the fuel cut-off specifications for the 1990-1991 "A, F, J, L, W" Cars equipped with 3.1L (VIN T) and 3.4L (VIN X) engines.

1990-1991 "W" cars with 3.1L engines: --------------------------------------- To prevent possible engine damage from over-speed the Electronic Control Module (ECM) "cuts-off" fuel from the injectors when engine speed is above approximately 6200 rpm with the vehicle in any forward gear or reverse, and approximately 4000 rpm in park or neutral. To prevent tire damage, the ECM also has a fuel cut-off in excess of 100 mph (161 km/h) based on speed rating of the tires.

1990-1991 "W" cars with 3.4L engines: -------------------------------------- To prevent possible engine damage from over-speed the Electronic Control Module (ECM) "cuts-off" fuel from the injectors when engine speed is above approximately 6500 rpm with the vehicle in any forward gear or reverse, and approximately 3000 rpm in park or neutral on vehicles equipped with automatic transmissions. On vehicles equipped with a manual transmission the fuel is cut-off at approximately 7000 rpm. To prevent tire damage, the ECM also has a fuel cut-off in excess of 120 mph (193 km/h) based on speed rating of the tires.

1990-1991 "A, F, J. L" cars with 3.1L engines: ----------------------------------------------- To prevent possible engine damage from over-speed the Electronic Control Module (ECM) "cuts-off" fuel from the injectors when engine speed is above approximately 6200 rpm. To prevent tire damage, the ECM also has a fuel cut-off in excess of 100 mph (161 km/h) based on speed rating of the tires.

When diagnosing any suspected fuel cut-off problems, carefully compare Tech 1 ("Scanner") engine rpm versus actual rpm. If the ECM is sensing rpm or vehicle speed in the fuel cut-off range due to Electro-Magnetic Interference (EMI) or other electrical "noise," thoroughly investigate harness routings and aftermarket equipment installations.

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.