DIESEL ENG. HESITATION, WHITE SMOKE, ROUGH IDLE, LACK OF PWR. GMC Truck GMC P RV/Van/Commercial Chassis 1996

SUBJECT: DIESEL ENGINE HESITATION, WHITE SMOKE, ROUGH IDLE, LACK OF POWER, HARD OR NO START, STALL (CHECK FOR DIESEL FUEL CONTAMINATION OR POOR FUEL QUALITY)

MODELS: 1994-98 CHEVROLET AND GMC C/K, G, P MODELS WITH 6.5L DIESEL ENGINE (VINS P, S, Y, F - RPOS L49, L56, L57, L65)

CONDITION:

SOME OWNERS OF THE ABOVE LISTED VEHICLES MAY COMMENT THAT THEIR VEHICLE HAS A ROUGH IDLE, LACKS POWER, IS DIFFICULT OR WON'T START, AND MAY OCCASIONALLY STALL. IN ADDITION, THE MIL (MALFUNCTION INDICATOR LAMP) OR WIF (WATER IN FUEL LAMP) MAY BE ILLUMINATED AND THERE MAY BE FUEL INJECTION PUMP DTC'S IN HISTORY.

DO NOT REPLACE THE FUEL INJECTION PUMP FOR THIS CONDITION WITHOUT FIRST ELIMINATING BOTH FUEL CONTAMINATION AND FUEL QUALITY AS SOURCES OF THE CUSTOMER'S CONCERN.

CAUSE:

THE DIESEL ENGINE FUEL SYSTEM MAY BE CONTAMINATED OR FUEL QUALITY MAY BE POOR. IF WATER, GASOLINE, OR OTHER CONTAMINANTS ARE IN THE DIESEL ENGINE FUEL SUPPLY, OR IF FUEL QUALITY IS POOR, DRIVEABILITY COMPLAINTS OR INJECTION PUMP DTC'S MAY BE SET. THE CONTAMINANTS MUST BE REMOVED AND THE FUEL SYSTEM FLUSHED PRIOR TO ANY REPAIRS OR DIAGNOSTICS BEING PERFORMED. IN ADDITION, A KNOWN GOOD SUPPLY OF FUEL MUST BE USED IN THE VEHICLE TO OBTAIN PROPER ENGINE PERFORMANCE.

CORRECTION:

IF A DRIVEABILITY CONDITION EXISTS, AND/OR IF DIESEL INJECTION PUMP DTC'S ARE PRESENT WHEN PERFORMING AN ON BOARD DIAGNOSTICS (OBD) SYSTEM CHECK, CHECK FOR FUEL SYSTEM CONTAMINATION AND VERIFY FUEL QUALITY PRIOR TO ANY OTHER REPAIRS. DO NOT REPLACE THE FUEL INJECTION PUMP WITHOUT FIRST ELIMINATING BOTH FUEL CONTAMINATION AND FUEL QUALITY AS SOURCES OF THE CUSTOMER'S CONCERN.

SEVERAL DIFFERENT TYPES OF CONTAMINATION CAN OCCUR IN DIESEL FUEL. FUNGI (MOLD), WATER, OR GASOLINE CAN SOMETIMES BE FOUND IN A DIESEL ENGINE FUEL SUPPLY. IN ADDITION, THE CUSTOMER MAY USE AN INCORRECT FUEL GRADE WHICH CAN CAUSE DRIVEABILITY OR MILEAGE CONCERNS.

TESTING FOR FUEL CONTAMINATION: IF FUNGI, WATER, OR GASOLINE CONTAMINATION ARE SUSPECTED, THE TECHNICIAN SHOULD FIRST INSPECT THE FUEL FILTER AND/OR FUEL FILTER HOUSING AS DESCRIBED IN THE ENGINE CONTROLS SECTION OF THE APPROPRIATE SERVICE MANUAL. FOR EXAMPLE THIS PROCEDURE IS LISTED IN THE 1998 C/K SERVICE MANUAL BOOK 4, ENGINE CONTROLS SECTION, PAGE 6- 2569.

WATER OR FUNGI (MOLD) IN THE FUEL SYSTEM: IF WATER OR FUNGI (MOLD) ARE DETECTED WHEN INSPECTING THE FUEL FILTER OR FILTER HOUSING, GO TO THE CLEANING WATER FROM THE FUEL SYSTEM PROCEDURE LISTED IN THE ENGINE CONTROLS SECTION OF THE APPROPRIATE SERVICE MANUAL. USING THE 1998 C/K AGAIN AS AN EXAMPLE, GO TO 1998 BOOK 4, ENGINE CONTROLS, CLEANING WATER FROM THE FUEL SYSTEM ON PAGE 6-2569. THIS SECTION HAS THE PROCEDURE FOR PURGING WATER FROM THE FUEL SYSTEM AND DESCRIBES WHEN TO USE A BACTERIA BIOCIDE.

GASOLINE IN THE FUEL SYSTEM: GASOLINE IS ALSO SOMETIMES INADVERTENTLY MIXED IN WITH DIESEL FUEL. THIS ALSO CAN LEAD TO NUMEROUS DRIVEABILITY CONDITIONS, UNUSUALLY HIGH FUEL RATES OBSERVED ON THE TECH 2, FUEL INJECTION PUMP AND NOZZLE DAMAGE, AND IF NOT ELIMINATED FROM THE FUEL SYSTEM, MULTIPLE TRIPS INTO THE DEALERSHIP FOR CUSTOMERS.

IF GASOLINE CONTAMINATION IS DETECTED WHEN CHECKING THE FUEL FILTER OR FILTER HOUSING, GO TO THE CLEANING GASOLINE FROM THE FUEL SYSTEM PROCEDURE LISTED IN THE ENGINE CONTROLS SECTION OF THE APPROPRIATE VEHICLE LINE SERVICE MANUAL. USING THE 1998 C/K AS AN EXAMPLE, THIS PROCEDURE IS FOUND IN BOOK 4, ENGINE CONTROLS SECTION, PAGE 6-2570.

WHAT TYPE OF DIESEL FUEL SHOULD A CUSTOMER USE?: POOR FUEL QUALITY MAY ALSO CAUSE DRIVEABILITY COMPLAINTS SUCH AS HESITATION, STALL, LACK OF POWER, SLOW OR NO START. FOR BEST RESULTS, NUMBER 2-D DIESEL FUEL SHOULD BE USED YEAR ROUND (ABOVE AND BELOW FREEZING TEMPERATURES) AS OIL COMPANIES BLEND NUMBER 2-D FUEL TO ADDRESS DIFFERENT CLIMATES. NUMBER 1-D DIESEL FUEL MAY BE USED IN VERY COLD TEMPERATURES, WHEN IT STAYS BELOW 0 DEGREES F (-18C). A POWER AND FUEL ECONOMY LOSS WILL OCCUR WHEN USING NUMBER 1-D FUEL. IN ADDITION, IF NUMBER 1-D FUEL, OR A 2-D WINTER BLEND, IS USED IN A WARM OR HOT CLIMATE (SUCH AS WHEN A VEHICLE IS SHIPPED FROM A COLD WEATHER AREA TO A WARM WEATHER AREA WITH THE TANK ALREADY FILLED WITH COLD WEATHER FUEL), STALLING, ROUGH IDLE, POOR OR NO START AND OTHER DRIVEABILITY SYMPTOMS MAY OCCUR WHEN THE ENGINE IS HOT. IN ADDITION, AN UNUSUALLY HIGH FUEL RATE MAY BE OBSERVED ON THE TECH 2 SCAN TOOL COMPARED TO A SIMILAR VEHICLE USING NUMBER 2-D FUEL.

SPECIFIC GRAVITY TESTING: IF DRIVEABILITY CONDITIONS EXIST SUCH AS ROUGH IDLE, STALLING, HARD OR NO START, CHECK FOR WATER OR GASOLINE IN THE FUEL FIRST. IF OK, CHECK FUEL SPECIFIC GRAVITY USING THE FUEL QUALITY HYDROMETER. THIS PROCEDURE PROVIDES A GENERAL INDICATION OF FUEL QUALITY. THE SPECIFIC GRAVITY TESTING PROCEDURE IS LISTED IN THE ENGINE CONTROLS SECTION OF THE SERVICE MANUAL. FOR EXAMPLE, 1998 C/K USE BOOK 4, ENGINE CONTROLS SECTION PAGE 6-2570. NUMBER 2-D FUEL SHOULD BE BETWEEN 30-39 API GRAVITY, AND NUMBER 1-D SHOULD BE BETWEEN 39-44 API GRAVITY. REFER TO THE SERVICE MANUAL CHART IN THE SPECIFIC GRAVITY TESTING SECTION FOR MORE DETAILS.

SUMMARY:

DO NOT REPLACE A FUEL INJECTION PUMP WITHOUT PERFORMING ALL NORMAL SERVICE MANUAL DIAGNOSTICS INCLUDING DTC'S, SYMPTOMS, AND A REVIEW OF THE CUSTOMERS COMMENTS. ALWAYS CHECK FOR FUEL QUALITY AND POSSIBLE CONTAMINATION. THIS IS CRITICAL TO PROPERLY DIAGNOSING A DIESEL ENGINE DRIVEABILITY COMPLAINT.

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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.