ENGINE DETONATION 4.1L V6 INSTALLATION OF PROM

A NEWLY CALIBRATED SERVICE PROM HAS BEEN RELEASED TO ALLEVIATE OR MINIMIZE HIGH SPEED, 55 MPH DETONATION (SPARK KNOCK) ON 1981 E/K CARS EQUIPPED WITH A 4.1L V-6 ENGINE. VEHICLE COMPONENTS AND SYSTEMS OTHER THAN THE PROM MAY ALSO CAUSE DETONATION. TO PROPERLY DIAGNOSE AND CORRECT A DETONATION CONDITION, FOLLOW THE SERVICE PROCEDURES OUTLINED IN THIS BULLETIN. SERVICE PROCEDURE I.DETERMINE THE DRIVING CONDITIONS DURING WHICH THE DETONATION OCCURS. LIGHT DETONATION EXPERIENCED WHILE ACCELERATING OR DRIVING UP HILLS, AT IDLE WITH A QUICK THROTTLE OPENING, AND/OR DURING MEDIUM THROTTLE OPENING WHEN THE THROTTLE IS RAPIDLY CLOSED SHOULD BE CONSIDERED NORMAL. DETONATION, OTHER THAN DESCRIBED ABOVE, IS ABNORMAL AND CAN BE ALLEVIATED OR MINIMIZED. II.FACTORS WHICH CAN CAUSE EXCESSIVE DETONATION ARE: ADVANCED IGNITION TIMING, HIGH COOLANT AND/OR AIR-FUEL MIXTURE TEMPERATURES, COMBUSTION CHAMBER DEPOSITS, ABSENCE OF EGR GASES, IMPROPER AIR-FUEL MIXTURES, AND LOW FUEL OCTANE QUALITY. THE LISTED ITEMS SHOULD BE VERIFIED TO ENSURE THAT THE ENGINE AND ITS CONTROL SYSTEMS ARE PERFORMING TO SPECIFICATIONS. 1.BASE IGNITION TIMING. REFER TO EMISSION CONTROL INFORMATION LABEL, LOCATED ON THE RADIATOR SUPPORT PANEL, FOR TIMING SPECIFICATIONS. 2.CORRECT DISTRIBUTOR WAVE WASHER. REFER TO SERVICEMAN BULLETIN T81-73, FILED IN GROUP 6D. 3.EST WIRING. WIRING MUST BE ROUTED AT LEAST ONE INCH FROM ANY SPARK WIRE. 4.SPARK PLUGS. R43TSX PLUGS SHOULD BE INSTALLED. 5.PROPER OPERATION OF COOLANT SENSOR, MAP SENSOR OR BARO SENSOR. 6.ENGINE OPERATING TEMPERATURE. CHECK FOR OBVIOUS OVERHEATING CONDITIONS (LOW COOLANT, LOOSE FAN BELT, RESTRICTED AIR FLOW, ETC.). 7.PROPER OPERATION OF EARLY FUEL EVAPORATION (EFE) VALVE. 8.PROPER THERMOSTATIC AIR CLEANER OPERATION. 9.DEPOSITS IN COMBUSTION CHAMBERS. 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 ALLOWED TO SOAK OVERNIGHT, SHOULD TEMPORARILY 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. 10.EGR SYSTEM. CHECK FOR: A.PROPER OPERATION OF EGR CONTROL SOLENOID. B.PROPER OPERATION OF EGR VALVE. C.CORRECT EGR VALVE APPLICATIONS FOR ENGINE. D.PLUGGED EGR PASSAGES IN THE CYLINDER HEAD OR INTAKE MANIFOLD. 11.VACUUM HOSES. CHECK FOR PLUGGED, OR PINCHED OR LEAKING HOSES. 12.FUEL SYSTEM. CHECK FOR RESTRICTIONS (I.E., PLUGGED FUEL FILTER, ETC.). 13.CARBURETOR. CHECK FOR STUCK METERING RODS. 14.FUEL. THIS ENGINE IS DESIGNED TO OPERATE ON A FUEL WITH AN OCTANE RATING OF 87 (R+M)/2; ANYTHING LESS CAN CAUSE ENGINE SPARK KNOCK. (REFER TO OWNER'S MANUAL FOR AN EXPLANATION OF OCTANE RATING AND HIGH ALTITUDE OCTANE RATING). III.IF THE ABOVE LISTED ITEMS ARE OPERATIONAL AND/OR PERFORMING TO SPECIFICATIONS AND EXCESSIVE HIGH SPEED DETONATION PERSISTS, INSTALL SERVICE PROM (P/N 1226079).

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.