BUZZ NOISE AT IDLE NEAR I/P OR FLOOR PAN

VEHICLES AFFECTED: 1987 R/V TRUCKS EQUIPPED WITH 5.0L (VIN CODE H), 5.7L (VIN CODE K), 4.3L (VIN CODE Z) OR 7.4L (VIN CODE N) ENGINES

Some 1987 R/V models equipped with TBI engines may have a condition where the fuel feed and return pipe assemblies have been mispositioned while the vehicle was being built. As a result, the pipes contact body sheet metal, causing an unacceptable injector pulse (buzzing) noise inside the truck near the dash or the floor pan at low idle speeds. This condition can be repaired using the following procedures.

Service Procedures

5.0L or 5.7L Engines

1. Remove the air cleaner assembly.

2. Inspect the fuel feed pipe (Figure 1) routing. The pipe is routed near an intake manifold vacuum boss on the rear manifold runner. Contact at this point pushes the pipe into the body dash cowl panel or transmission tunnel. If pipe contact is evident, reposition the pipe away from the vacuum boss. It should not be necessary to disconnect or unclip the pipes to reposition them.

3. Reinstall the air cleaner and retest the truck.

4.3L and 7.4L Engines

1. Remove the air cleaner assembly.

2. Inspect the fuel pipes as they pass near the floor pan and the dash cowl panel (Figures 2 and 3). The pipes must have a 1.27 cm (1/2") clearance between the floor pan and dash cowl panel. If the pipes contact the floor pan or dash cowl panel, reposition the pipes away from the floor pan or dash cowl panel. It may be necessary to raise the truck to gain access to the pipes as they pass near the floor pan. It should not be necessary to disconnect or unclip the pipes to reposition them.

3. Reinstall air cleaner and retest truck.

All Engines with TBI

It may be necessary to reposition the intermediate feed and/or return pipes mounted on the frame (Figure 4) to eliminate contact with the floor pan or transmission tunnel. Reposition the pipes as necessary.

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.