EXCESSIVE SPARK KNOCK -PING INOPERATIVE EGR VALVE

INOPERATIVE EGR VALVES

MODELS AFFECTED: SOME 1986 CENTURYS, SOMERSETS, --------------- AND SKYLARKS EQUIPPED WITH 2.5L ENGINES (VIN CODES R AND U)

Some 1986 vehicles equipped with 2.5L engines may exhibit excessive spark knock, at part throttle, due to an inoperative EGR valve.

If an EGR valve has been diagnosed as inoperative because it does not respond to a normal vacuum signal, remove the vacuum hose from the valve and check the orifice in the vacuum hose fitting of the valve for a plugged condition. The orifice may have an excessive build up of hose assembly lubricant that has hardened and is restricting vacuum. If this condition exists, clear the orifice with a small wire, or pin, and reinstall the vacuum hose to the fitting and test the EGR valve for function.

If the EGR valve is still inoperative, replace it.

Use applicable labor operation number and labor time.

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.