INFO. ON PERCEIVED LOW POWER UNDER SOME ROAD/LOAD CONDITION

SUBJECT: INFORMATION ON PERCEIVED LOW POWER

VEHICLES AFFECTED: 1987-93 "C,K,G,P,R,V" TRUCKS WITH 7.4L ENGINES (VIN N,RPO L19) WITH TBI FUEL SYSTEMS

Some owners with GM trucks equipped with 7.4 litre throttle body injection (TBI) V8 engines may complain of low power under some road/load conditions.

Engines equipped with TBI fuel systems respond differently to accelerator pedal positions than those engines equipped with a 4-barrel carburetor. While a TBI system and a carburetor accomplish the same task, the TBI system maintains a constant air to fuel (A/F) ratio over different road/load conditions and air flow rates. (Refer to Figure).

The air flow curve of the TBI unit has a more uniform, smooth response as the throttle angle increases. The flow curve of the carburetor shows the characteristic 'sudden jump' in flow rate as the secondary throttle plates open. Since a TBI unit does not have secondary throttle plates, there is no sudden increase in flow when the accelerator pedal is suddenly depressed from part throttle to W.O.T.

By using a TBI fuel system, improvements in cold startability, smoother engine operation, increased fuel economy, and improved exhaust emissions are obtained.

Customers may perceive little or no noticeable increase in engine power between throttle positions of 3/4 open (60 degree throttle angle) and wide open (80 degree throttle angle) under some road/ load conditions. Extensive tests have shown the engine is not losing power in these situations.

Assuming all components and systems are operating correctly, no further action is required.

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.