FUEL LINE KNOCK NOISE REPAIR AND PARTS DESCRIBED

MODELS AFFECTED: 1987-88 CENTURYS WITH THE LB6 2.8L V-6 ENGINE (VIN CODE W)

Some 1987-88 Centurys with 2.8L MPFI engines may exhibit a light hammering/knocking type noise audible in the vehicle passenger compartment. The noise condition may be noted in a cold start mode, and/or warm stabilized mode and is most apparent at engine idle.

This condition may be caused by pressure pulsations in the fuel system generated by fuel injector operation, resulting in hydraulic hammering in chassis fuel pipes.

Vehicles exhibiting this condition may be repaired by installation of the part(s) noted below by model year, following the service procedure in this bulletin.

PART REQUIREMENT BY MODEL YEAR PART NUMBER PART DESCRIPTION 1987 1988 ----------- ---------------- ------------------------------ 10115809 Fuel Feed Pipe Expansion 1 1 Chamber Assembly

10093228 Fuel Return Hose Stand 1 Pipe Assembly

Service Procedure:

1. Disconnect negative battery cable and remove fuel tank filler cap.

2. Relieve pressure in fuel system following shop manual procedure.

3. Disconnect fuel feed and return hoses at engine fuel feed and return pipes utilizing backup wrench on fittings.

4. On 1987 model vehicles only, disconnect fuel return hose at chassis fuel return pipe utilizing backup wrench on fitting and discard hose assembly.

5. Remove bolt securing engine fuel feed and return pipe bracket at cylinder head.

6. Remove oil fill cap and disconnect vacuum line and the idle air control valve electrical connector at the throttle body.

7. Disconnect fuel return pipe and then fuel feed pipe at fuel rail fittings utilizing backup wrench.

8. Position pipes to gain access to bolt securing pipe clip to engine bracket and remove bolt.

9. Remove feed pipe from clip and discard.

10. Torque fuel rail feed and return fittings to 20-26 N.m.

11. Install new fuel feed pipe expansion chamber assembly, Part Number 10115809 and insert into retaining clip (See Figure 1).

12. Install retaining clip to engine bracket torquing bolt to 4.5-7 N.m.

13. Connect fuel feed and then fuel return pipe to fuel rail, torquing fittings to 20-26 N.m utilizing backup wrench.

14. Install engine bracket to cylinder head torquing bolt to 40-60 N.m.

15. On 1987 model vehicles only, connect the new fuel return hose - stand pipe assembly, Part Number 10093228, to chassis fuel return pipe as shown in Figure 2. Torque fitting to 20-34 N.m utilizing backup wrench and ensuring stand pipe is maintained in a vertical position.

16. Connect fuel feed and return hoses to engine feed and return pipes. Torque fittings to 20-34 N.m utilizing backup wrench on fittings.

17. Install oil fill cap and connect vacuum line and electrical connector.

18. Connect negative battery cable and install fuel tank cap.

19. Start engine, check all connections for possible leaks, and correct as required.

WARRANTY INFORMATION

Labor Operation Number: T1193 Labor Time: .7 Hour (1988 Model Year) .9 Hour (1987 Model Year) Trouble Code: 92

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.