DRIVEABILITY & EMISSION CHANGES MADE TO IMPROVE DRIVE. Chevrolet Chevy MD Conventional 97.5" 1989

JULY 15, 1988

TO: GM MEDIUM DUTY TRUCK DEALERS

SUBJECT: DRIVEABILITY MEDIUM DUTY TRUCKS 6.0L (366 CID VIN CODE "B") 7.0L (427 CID VIN CODE "E")

ON JANUARY 1, 1985, A NEW LEVEL OF FEDERAL EMISSION REQUIREMENTS (REFERRED TO AS H5D) BECAME EFFECTIVE. TRUCK + BUS IMPLEMENTATION OF CHANGES REQUIRED TO MEET THESE STANDARDS IN SOME CASES RESULTED IN SOME DRIVEABILITY CONCERNS WHICH HAVE BEEN DESCRIBED AS SAG, HESITATION,FAILS TO RUN, BACK FIRE, SURGE, LOSS OF POWER, OR VAPOR LOCK.

WE HAVE MADE MANY CHANGES TO ELIMINATE THESE SYMPTOMS. ON JUNE 6, 1988, WE BEGAN BUILDING GASOLINE POWERED MEDIUM DUTY TRUCKS WITH IN-TANK ELECTRIC FUEL PUMPS TO ELIMINATE "VAPOR LOCK", THE LAST OF THE IDENTIFIED 6.0L AND/OR 7.0L DRIVEABILITY CONCERNS (GMC SERVICE BULLETIN 88-T-120). AS OF THE SAME DATE, CHANGES TO AIR SYSTEM AND CARBURETORS WERE INCLUDED AS WELL. A BULLETIN DESCRIBING THESE WILL BE RELEASED IN THE NEAR FUTURE.

WE ARE PLEASED WITH THE TEST RESULTS DELIVERED BY ENGINEERING VEHICLES EQUIPPED WITH THE LATEST DESIGN MATERIAL INCLUDING THE SUBMERGED FUEL PUMP.

TO INSURE OUR CHANGES ARE EFFECTIVE IN ELIMINATING DRIVEABILITY CONCERNS ON THE 6.0L AND 7.0L ENGINES, WE ASK YOU TO QUALIFY MEDIUM DUTY (PONTIAC PRODUCED VIN PLANT CODE 'V") 6.0L AND 7.L) GAS ENGINE DRIVEABILITY CONCERNS BY THE FOLLOWING CRITERIA:

. IS THE VEHICLE 1988 OR 1989 YEAR (VIN POSITION 10 IS "J" OR "K")?

. IS THE ENGINE CODE IN THE VIN "B" OR "E" (CHARACTER POSITION 8)?

. IS THE VIN SEQUENCE NUMBER FOR 1988 YEAR TRUCKS (LAST 6 CHARACTERS OF THE VIN) GREATER THAN 116489 FOR CHEVROLET NAME PLATE OR GREATER THAN 530425 FOR GMC NAME PLATE OR IS THE VEHICLE YEAR 1989 (ALL OF WHICH WILL BE BUILT WITH THE LATEST DRIVEABILITY CHANGES)?

IF THE ANSWER TO ANY OF THE ABOVE QUESTIONS IS NO AND YOU NEED ASSISTANCE TO FIX THE TRUCK, PLEASE CALL TECHNICAL ASSISTANCE FOR CORRECTIVE RECOMMENDATIONS.

VEHICLES THAT MEET ALL OF THE ABOVE CRITERIA ARE ESPECIALLY IMPORTANT TO YOU AND TO TRUCK + BUS BECAUSE THESE VEHICLES WERE BUILT WITH THE LATEST DRIVEABILITY CHANGES, AND IF THESE CHANGES DO NOT PROVIDE PERFORMANCE TO MEET YOUR CUSTOMER'S EXPECTATIONS WE WILL BOTH SUFFER IN THE MARKETPLACE. WE REQUEST YOU PROCESS ANY DRIVEABILITY CONCERNS ON THESE QUALIFIED VEHICLES FOR THE REMAINDER OF THE 1988 CALENDAR YEAR IN THE FOLLOWING MANNER:

1. IF YOUR SERVICE TECHNICIAN DIAGNOSES THE CONDITION AND CORRECTS IT WITHOUT HELP FROM GM, PLEASE COMPLETE A PRODUCT REPORT WHILE YOU ARE ENTERING YOUR DCS WARRANCY CLAIM. INSTRUCTIONS WERE INCLUDED IN OUR PUBLICATION "WHATS NEW" DATED MARCH, 1988, AND ARE ATTACHED AS WELL. YOUR SERVICE MANAGER WAS INSTRUCTED IN PRODUCT REPORT SUBMISSION DURING THE RECENT SERVICE IDEA EXCHANGE MEETINGS.

2. IF YOUR SERVICE DEPARTMENT NEEDS HELP TO CORRECT A DRIVEABILITY CONCERN ON ANY MEDIUM DUTY TRUCK CALL TECHNICAL ASSISTANCE FOR THEIR ASSISTANCE IN CORRECTING THE CONDITION. THE TAC SERVICE ENGINEER WILL OPEN A TAC CASE, RECORD THE CONDITION DETAILS IN THE CASE RECORD, AND ASSIST YOU IN RESOLVING THE CONDITION.

TAKING THIS ACTION WILL INSURE AN ACCURATE ASSESSMENT OF 6.0L AND 7.0L DRIVEABILITY IMPROVEMENTS.

J. B. GIFFIN, MANAGER PRODUCT SERVICE

JBG:EB

CC: R.L. BECKER ZONE SERVICE MANAGERS R. G. CAMERON FLEET SERVICE MANAGERS G. M. COMPAGNONI DISTRICT SERVICE MANAGERS R. L. HELLER SERVICE DEVELOPMENT MANAGERS J. S. KANE TAC SERVICE ENGINEERS K. M. POPIS D. L. PORTER J. S. VICINI

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.