CONTINUOUS SPARK KNOCK OR EXCESSIVE OIL CONSUMPTION

REVISED: 05/08/95

THIS BULLETIN IS BEING REVISED TO ADD RIVIERA MODELS.

SUBJECT: CONTINUOUS SPARK KNOCK OR EXCESSIVE OIL CONSUMPTION (REPLACE VALVE STEM SEALS)

MODELS: 1993 BUICK RIVIERA 1995 BUICK RIVIERA 1993-95 BUICK LESABRE, PARK AVENUE, REGAL 1993-95 CHEVROLET LUMINA APV 1993-95 OLDSMOBILE EIGHTY EIGHT, NINETY EIGHT, SILHOUETTE 1993-95 PONTIAC BONNEVILLE, TRANS SPORT WITH 3800 ENGINE (VINS 1 OR L - RPOS L67 OR L27)

VEHICLES BUILT BEFORE NOVEMBER 1, 1994.

CONDITION:

SOME OWNERS MAY COMMENT ABOUT A CONTINUOUS SPARK KNOCK DURING NORMAL DRIVING CONDITIONS AND/OR EXCESSIVE OIL CONSUMPTION.

CAUSE:

THE CONDITION MAY BE CAUSED BY ONE OR MORE VALVE STEM SEALS WITH A BROKEN RETAINING BAND. A BROKEN VALVE STEM SEAL RETAINING BAND DISTORTS THE SEAL ALLOWING OIL TO BE DRAWN DOWN THE VALVE GUIDE AND INTO THE COMBUSTION CHAMBER. **REFER TO ILLUSTRATION.** WHEN OIL IS BURNED INSIDE THE COMBUSTION CHAMBER, THE EFFECTIVE OCTANE RATING IS LOWERED CONSIDERABLY AND THEREFORE LEADS TO SPARK KNOCK. FURTHERMORE, THE RESULTING CARBON DEPOSIT BUILD UP INSIDE THE COMBUSTION CHAMBER WILL RAISE THE EFFECTIVE COMPRESSION RATIO, AGGRAVATING THE SPARK KNOCK CONDITION.

SERVICE INFORMATION TO DIAGNOSE THE CONDITION, THE TECHNICIAN SHOULD DRIVE THE VEHICLE WITH A SCAN TOOL INSTALLED. CHECK FOR AND REPAIR ANY DIAGNOSTIC CODES THAT MAY BE SET. IF SCANNER READINGS APPEAR TO BE NORMAL, THEN PROGRAM THE SCAN TOOL TO OBSERVE ELECTRONIC SPARK CONTROL (ESC) ACTIVITY. LIGHTLY ACCELERATE THE VEHICLE WHILE MONITORING FOR ESC ACTIVITY AND LISTEN FOR AUDIBLE SPARK KNOCK. IF ESC IS CONSTANTLY ACTIVE UNDER LIGHT TO MEDIUM ACCELERATION AND AUDIBLE SPARK KNOCK PRESENT, THEN PERFORM THE FOLLOWING:

1. INSURE THAT GASOLINE QUALITY IS NOT THE CAUSE OF THE CONDITION.

2. ASK THE VEHICLE OWNER IF THERE HAS BEEN ANY NOTICEABLE OIL CONSUMPTION.

***IMPORTANT*** FIELD DATA SUGGESTS THAT THE CONTINUOUS SPARK KNOCK CONDITION CAN OCCUR IN SOME VEHICLES AS A RESULT OF CONSUMING ONE QUART OF OIL IN TWO THOUSAND MILES. FIELD DATA FURTHER SUGGESTS THAT CONSUMING ONE QUART OF OIL IN THREE THOUSAND MILES DOES NOT RESULT IN CONTINUOUS SPARK KNOCK.

3. REMOVE ALL SPARK PLUGS AND VISUALLY INSPECT THE PLUGS FOR ANY EVIDENCE OF OIL CONSUMPTION OR OIL FOULING.

4. IF AN OIL FOULED PLUG IS FOUND, AS DESCRIBED IN STEP 3, REMOVE THE VALVE COVER ON THE AFFECTED BANK(S).

5. IF NO SUSPICIOUS SPARK PLUG IS FOUND, REMOVE BOTH VALVE COVERS.

6. REMOVE THE INTAKE AND EXHAUST VALVE SPRINGS FROM THE SUSPECT CYLINDER(S).

7. REMOVE THE VALVE STEM SEALS FROM THE SUSPECT CYLINDER(S).

8. INSPECT THE REMOVED VALVE SEALS FOR A BROKEN RETAINING BAND. REFER TO THE ILLUSTRATION.

9. REPLACE SEALS THAT HAVE BROKEN RETAINING BANDS WITH NEW SEALS.

10. REASSEMBLE THE ENGINE.

11. RUN GM TOP ENGINE CLEANER THROUGH THE ENGINE TO REMOVE EXCESSIVE CARBON DEPOSIT BUILD UP.

- WARM THE ENGINE UP TO OPERATING TEMPERATURE. - REMOVE THE FUEL PRESSURE REGULATOR VACUUM HOSE WHERE IT CONNECTS TO THE VACUUM TREE. - INSTALL A LENGTH OF DEALER SUPPLIED VACUUM HOSE TO THE VACUUM TREE. - INJECT GM TOP ENGINE CLEANER THROUGH THE DEALER SUPPLIED VACUUM HOSE WITH THE ENGINE RUNNING AT ABOUT 1000 RPM UNTIL THE SPRAY CAN IS EMPTY. - REINSTALL THE ORIGINAL FUEL PRESSURE REGULATOR VACUUM HOSE.

12. TEST DRIVE AND VERIFY THAT THE CONDITION HAS BEEN CORRECTED AS OUTLINED IN THE "SERVICE INFORMATION" SECTION IN THIS BULLETIN.

*** INSERT ILLUSTRATION HERE ***

PARTS INFORMATION

DESCRIPTION PART NUMBER INTAKE VALVE STEM SEAL 25535162 EXHAUST VALVE STEM SEAL 24501395 GM TOP ENGINE CLEANER 1052626

PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

WARRANTY INFORMATION FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OPERATION DESCRIPTION LABOR TIME

SPRING, CAP AND/ OR SEAL, VALVE - REPLACE

J0540 ONE CYL - RIGHT BANK USE PUBLISHED LABOR TIMES

J0541 ONE CYL - LEFT BANK USE PUBLISHED LABOR TIMES

J0547 BOTH BANKS USE PUBLISHED LABOR TIMES

ADD - A EACH ADDITIONAL CYL USE PUBLISHED LABOR TIMES

ADD - B REPLACE ALL USE PUBLISHED LABOR TIMES

FIGURES: 1 ATTACHMENTS: 0

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.

COPYRIGHT 1995 GENERAL MOTORS CORPORATION. ALL RIGHTS RESERVED.