Engine - Excessive Spark Knock at Part Throttle
Bulletin 86-6E-9Date
Apr. 86
Ref. No. 86-110-6E
SUBJECT: 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.