INFO. ON 1997 TRUCKS WITH 6.5L DIESEL ENGINE PRODUCTS UPDATES. GMC Truck GMC P52 RV/Van Chassis 1997

REVISION: 05/19/97

THIS BULLETIN IS BEING REVISED TO INCLUDE THAT ALL 1997 6.5L DIESEL ENGINES AND GOODWRENCH ENGINES INCORPORATE OIL SPRAY PISTON COOLING. PLEASE DISCARD CORPORATE BULLETIN 67-61-20 (SECTION 6-ENGINE). ----------------------------------------------------------------------

SUBJECT: INFORMATION ON 1997 TRUCKS WITH 6.5L DIESEL ENGINE PRODUCT UPDATES

MODELS: 1997 CHEVROLET AND GMC C/K, G AND P TRUCKS WITH 6.5L DIESEL ENGINE (VINS F, S, Y - RPOS L65, L56, L57)

THE RUNNING OIL PRESSURES ARE LOWER THAN PREVIOUS MODEL YEARS THAT IS A RESULT OF THE NEW SYSTEM. THE MINIMUM HOT OIL PRESSURE SPECIFICATION HAS BEEN REVISED TO 6 PSI AT IDLE AND 30 PSI AT 2000 RPM, WITH A MECHANICAL GAGE.

THE FOLLOWING PRODUCT UPDATES HAVE BEEN IMPLEMENTED ON THE 6.5L DIESEL ENGINE FOR THE 1997 MODEL YEAR. THE INFORMATION LISTED IS A BRIEF OVERVIEW; SEE YOUR 1997 SERVICE MANUAL FOR COMPLETE DETAILS.

OIL SPRAY PISTONS THERE ARE OIL SPRAY NOZZLES PRESS-FIT INTO THE BLOCK. THE OIL SPRAY NOZZLES DIRECT OIL TO THE UNDERSIDE OF THE PISTONS. THE PURPOSE OF SPRAYING OIL TO THE UNDERSIDE OF THE PISTON IS TO DECREASE PISTON TEMPERATURES TO INCREASE THE OVERALL "LIFE" OF THE ENGINE.

OIL PUMP THE OIL PUMP DISPLACEMENT HAS BEEN INCREASED AND USES A 552KPA (80 PSI) PRESSURE REGULATOR SPRING FOR ALL APPLICATIONS.

REDUCTION OF FUEL PULL OUT FUEL PULL OUT NOW OCCURS AT 245 DEGREES FAHRENHEIT FOR ENGINE OVERHEAT PROTECTION.

DUAL MASS FLYWHEEL IT HAS BEEN REPLACED FOR THE 1997 MODEL YEAR WITH A SINGLE PIECE MANUAL TRANSMISSION FLYWHEEL.

AIR CLEANERS THE 1997 MODEL YEAR INCORPORATES TWO TYPES OF AIR CLEANER. ONE TYPE IS FOR VEHICLES OPERATING IN A DUSTY/DIRTY (OFF ROAD) ENVIRONMENT (RPO K47) AND THE OTHER TYPE IS USED FOR ON HIGHWAY/CITY (NON DUSTY) TYPE ENVIRONMENT. ALSO, A RESTRICTION INDICATOR LOCATED BETWEEN THE AIR CLEANER AND TURBOCHARGER INDICATES WHEN TO CHANGE THE AIR CLEANER. IF THE CLEAR SECTION OF THE RESTRICTION INDICATOR IS GREEN, THEN NO SERVICE IS REQUIRED. WHEN THE INDICATOR IS ORANGE, THE FILTER SHOULD BE REPLACED.

FUEL INJECTION PUMP CONTACT TECHNICAL ASSISTANCE PRIOR TO REMOVAL OF THE INJECTION PUMP. AN ENHANCED FUEL INJECTION PUMP WAS RELEASED BEGINNING WITH THE 1997 MODEL YEAR THAT CONTAINS AN IMPROVED OPTICAL SENSOR. ALSO, THE PUMP CONTAINS NEW CERAMIC ROLLERS WHICH HELP PREVENT ROLLER WEAR DUE TO LOW LUBRICITY FUELS.

OIL PRESSURE GAGE THE 1997 TRUCKS OIL PRESSURE GAGE MAY FLUCTUATE WITH ENGINE SPEED CHANGES. THE MOVEMENT OF THE GAGE IS NORMAL. THE CONDITION IS MOST PREVALENT WITH ENGINES AT OPERATING TEMPERATURES. WHEN THE ENGINE IS COLD, THE GAGE MAY READ AS HIGH AS 80 PSI AT IDLE. THE OIL PRESSURE GAGE CAN READ AS LOW AS 20 PSI AT IDLE WHEN THE ENGINE IS AT OPERATING TEMPERATURES (MECHANICAL GAGE TO BLOCK WILL INDICATE APPROXIMATELY 9-12 PSI BECAUSE THE DASH GAGE IS NON LINEAR). THE MINIMUM SPECIFICATION IS 6 PSI, HOT OR IDLE.

TECH 2 TECH 2 INSTEAD OF TECH 1 IS NOW USED ON 1997 VEHICLES FOR ALL SCAN TOOL ASPECTS.

MASS AIR FLOW THE L56 ENGINE INCORPORATES A MASS AIR FLOW SENSOR (MAF) USED ONLY FOR CONTROLLING EGR FLOW (NOT FUELING).

ENHANCED DIAGNOSTICS ENHANCED DIAGNOSTICS WITH ADDITIONAL DTCS ASSOCIATED WITH EGR AND MAF FOR THE L56 (RPO) ENGINE.

EGR DTCS (L56) THE ALM (ADAPTIVE LEARN MATRIX) MUST BE RESET AFTER REPAIRS OF THE EGR SYSTEM. THE RESET IS UNDER THE SPECIAL FUNCTIONS IN THE SCAN TOOL. IF THE ALM IS NOT RESET AFTER A REPAIR OF THE EGR SYSTEM, IT WILL RESULT IN POOR DRIVEABILITY, HEAVY BLACK SMOKE, AND POSSIBLE DTCS.

TDC LEARN THE 1997 PROCEDURE WILL OVERWRITE THE PREVIOUS TDC LEARN, UNLIKE 1996 WHICH CLEARED THE TDC LEARN TO ZERO ON THE SCAN TOOL.

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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.