SPARK KNOCK CAUSED BY BRAKE PEDAL PRESSURE/SWITCH ADJUST.

WHEN DIAGNOSING SPARK KNOCK COMMENTS ON LATE 1981 CUTLASS, 88 MODELS AND 1982 CUTLASS SUPREME, 88 MODELS EQUIPPED WITH A 3.8L V6 ENGINE, BE SURE THE OWNER IS NOT RESTING THEIR LEFT FOOT ON THE BRAKE PEDAL WHICH WILL ACTIVATE THE EGR CUTOFF SOLENOID CAUSING THE EGR VALVE TO TURN OFF. ALSO BE SURE THE BRAKE SWITCH IS ADJUSTED PROPERLY. SPARK KNOCK 1981-82 3.8L V-6 AN OCCASIONAL LIGHT SPARK KNOCK WHILE ACCELERATING OR DRIVING UP HILLS SHOULD BE NO CAUSE FOR CONCERN. UNDER THIS MODE, LIGHT SPARK KNOCK INDICATES THAT THE GREATEST FUEL ECONOMY IS BEING ACHIEVED. TWO OTHER CONDITIONS WHERE THE ENGINE MIGHT SPARK KNOCK BUT WOULD BE CONSIDERED NORMAL ARE: A.AT IDLE WITH A QUICK THROTTLE OPENING; 2 OR 3 CYLINDERS MAY KNOCK UNTIL THE ECM RE-ADJUSTS TIMING. B.DURING MEDIUM THROTTLE OPENING WHEN THROTTLE IS RAPIDLY CLOSED; 2 OR 3 CYLINDERS MAY KNOCK UNTIL THE ECM RE-ADJUSTS TIMING. ENGINE SPARK KNOCK OTHER THAN DESCRIBED ABOVE IS ABNORMAL AND CAN BE CORRECTED. NORMALLY THREE THINGS CAUSE AN ENGINE TO SPARK KNOCK. 1.FUEL OCTANE RATING BELOW REQUIREMENTS. 2.INCORRECT IGNITION TIMING. 3.LEAN FUEL MIXTURE; INCORRECT EGR OPERATION. THE OLDSMOBILE SERVICE GUILD PRODUCT TRAINING MANUAL ALTHOUGH IT IS NOT COMMON, AN ABNORMALLY HIGH COMPRESSION RATIO CAN CAUSE THE ENGINE TO SPARK KNOCK AT WIDE OPEN THROTTLE. THIS SPARK KNOCK MAY ALSO BE HEARD UNDER LIGHT THROTTLE. SPARK KNOCK UNDER THESE CONDITIONS IS GENERALLY CAUSED BY EXCESSIVE CARBON BUILD-UP ON THE PISTON OR CYLINDER HEAD. A CAN OF GM TOP ENGINE CLEANER OR EQUIVALENT WHEN PROPERLY USED SHOULD CORRECT SPARK KNOCK CAUSED BY CARBON BUILD-UP. IF THE CONDITION RETURNS, DETERMINE WHAT IS CAUSING THE EXCESSIVE CARBON BUILD-UP. LEAKING INTAKE VALVE STEM SEALS SHOULD NOT BE OVERLOOKED. FUEL THIS ENGINE IS DESIGNED TO OPERATE ON A FUEL WITH AND OCTANE RATING OF 87, ANYTHING LESS CAN CAUSE ENGINE SPARK KNOCK. (SEE OWNERS MANUAL FOR AN EXPLANATION OF OCTANE RATING AND HIGH ALTITUDE OCTANE RATING). IGNITION TIMING EXCESSIVELY ADVANCED IGNITION TIMING CAN CAUSE A PING OR SPARK KNOCK CONDITION. THIS KNOCK IS THE RESULT OF PREMATURE COMBUSTION OF THE AIR FUEL MIXTURE WORKING AGAINST THE ROTATION OF THE ENGINE. ITEMS WHICH CAN AFFECT IGNITION TIMING AND CAUSE SPARK KNOCK 1.BASE IGNITION TIMING TOO FAR ADVANCED. 2.ABNORMALLY HIGH ENGINE OPERATING TEMPERATURE. 3.CHECK FOR PROPER OPERATION OF: COOLANT SENSOR MAP SENSOR BARO SENSOR 4.CHECK FOR CORRECT DISTRIBUTOR WAVE WASHER. 5.UNSHIELDED EST WIRING MUST BE ROUTED AT LEAST ONE INCH FROM ANY SPARK WIRE. ITEMS WHICH MAY CAUSE A LEAN FUEL MIXTURE EGR SYSTEM: 1.THE EGR SYSTEM IS DESIGNED TO INTRODUCE EXHAUST GASES THROUGH THE INTAKE MANIFOLD INTO THE ENGINE CYLINDERS. THESE EXHAUST GASES LOWER THE COMBUSTION TEMPERATURES WHICH IN TURN REDUCE OXIDES OF NITROGEN TO AN ACCEPTABLE LEVEL. THEREFORE, IMPROPER EGR SYSTEM OPERATION CAN CAUSE A LEAN AIR FUEL MIXTURE WHICH PERMITS EXCESSIVELY HIGH COMBUSTION TEMPERATURES TO DEVELOP. THE EXCESSIVELY HIGH COMBUSTION TEMPERATURES RESULT IN THE IGNITING OF THE LEAN AIR FUEL MIXTURE PRIOR TO SPARK PLUG FIRING, CAUSING THE ENGINE TO PING OR SPARK KNOCK. CHECK FOR: PROPER OPERATION OF EGR CONTROL SOLENOID PROPER OPERATION OF EGR CUTOUT RELAY. (STALL TESTING THE ENGINE WITH FOOT ON BRAKE PEDAL WILL CAUSE EGR CUTOUT RELAY TO ENERGIZE AND CUTOUT EGR, CAUSING ENGINE TO SPARK KNOCK. THIS IS A NORMAL CONDITION.) PROPER OPERATION OF EGR VALVE. CORRECT EGR VALVE APPLICATION FOR ENGINE. PLUGGED EGR PASSAGES IN THE CYLINDER HEAD OR INTAKE MANIFOLD. EGR SYSTEM DIAGNOSIS CAN BE FOUND ON PAGE 6E-63 AND EGR VALVE CHECK ON PAGE 6E-49 OF THE 1982 CHASSIS SERVICE MANUAL. 2.PLUGGED, OR PINCHED OR LEAKING VACUUM HOSES. 3.PROPER OPERATION OF EARLY FUEL EVAPORATION (EFE) VALVE 4.RESTRICTED FUEL SYSTEM IE: PLUGGED FUEL FILTER ETC. SPARK KNOCK 1981 AND 1982 3.8L V6 1981 AND 1982 MODELS EQUIPPED WITH THE 3.8L V6 GAS ENGINE AND AN EGR CUTOUT RELAY, MAY SPARK KNOCK IF ACCELERATED WITH THE 4 WAY HAZARD FLASHERS OPERATING. THIS OCCURS BECAUSE THE RELAY CYCLES WITH THE FLASHERS. SPARK KNOCK OCCURRING UNDER THIS CONDITION SHOULD BE CONSIDERED NORMAL.

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.