SMU - SECTIONS 3 AND 4 SERVICE TIMING PROCEDURE. GMC Truck GMC Suburban

SUBJECT: SERVICE MANUAL UPDATE - SECTIONS 3 AND 4 - SERVICE TIMING PROCEDURES FOR ELECTRONIC INJECTION PUMPS

MODELS: 1994 CHEVROLET AND GMC C/K, P TRUCKS AND G VAN EQUIPPED WITH 6.5L DIESEL ENGINES (VINS F, P, S - RPOS L65, L49, L56)

THE TIMING PROCEDURES IN THIS BULLETIN ARE INTENDED TO CLARIFY CURRENT PUBLISHED PROCEDURES AND TO COVER SITUATIONAL CONDITIONS. THESE PROCEDURES CAN BE FOUND UNDER "ON VEHICLE SERVICE," SECTIONS 3 AND 4 OF THE DRIVEABILITY AND EMISSIONS (DIESEL) MANUAL.

THREE DIFFERENT TIMING PROCEDURES ARE EXPLAINED BELOW ALONG WITH CONDITIONS UNDER WHICH EACH PROCEDURE IS TO BE USED.

1. TDC OFFSET LEARN PROCEDURE -------------------------- USE WHEN EITHER THE PCM AND/OR CRANK SENSOR OR COMPLETE NEW ENGINE IS INSTALLED.

2. INJECTION PUMP TIMING ADJUSTMENT OR CHECKING -------------------------------------------- USE WHEN EITHER THE PUMP TIMING MUST BE VERIFIED OR ADJUSTED, OR WHEN THE INJECTION PUMP HAS BEEN REPLACED.

3. BACK-UP TIMING PROCEDURE ------------------------ USE WHEN PROCEDURES 1 AND/OR 2 DO NOT APPLY.

PROCEDURES:

PROCEDURE 1 - TDC OFFSET LEARN PROCEDURE (SECTION 3)

USE **ONLY** WHEN ONE OF THE FOLLOWING HAS OCCURRED:

1. A **NEW** OR **DIFFERENT** PCM IS INSTALLED.

2. A **NEW** OR **DIFFERENT CRANK POSITION SENSOR** IS INSTALLED.

3. A **NEW** OR **DIFFERENT CRANK SENSOR** AND **PCM** ARE INSTALLED.

4. A **COMPLETE NEW ENGINE** IS INSTALLED.

THIS PROCEDURE ALLOWS THE PCM MEMORY TO BE UPDATED WITH THE CORRECT TDC OFFSET FOR THE ENGINE. DTC 88 WILL BE STORED UNTIL THIS PROCEDURE HAS BEEN COMPLETED WHEN A NEW PCM IS INSTALLED. PROCEED AS FOLLOWS:

- BATTERY IS FULLY CHARGED. - ENGINE OPERATING AT IDLE. - VEHICLE AT OPERATING TEMPERATURE. - CONNECT TECH 1 SCAN TOOL. - SELECT "OUTPUT TESTS" AND "INJ PUMP." - ACTIVATE "TDC LEARN." (REFER TO TECH 1 SCAN TOOL FOR PROPER WAY TO ACTIVATE "TDC LEARN.")

NOTICE: IT TAKES PCM 20 SECONDS TO LEARN "TDC OFFSET." ALLOW TECH 1 TO TIME OUT ("ON" WILL APPEAR AT BOTTOM RIGHT OF SCREEN WHEN ACTIVATED).

- VERIFY "TDC OFFSET" IN DATA LIST. - DTC 88 WILL BE STORED IF PROCEDURE HAS NOT BEEN DONE CORRECTLY.

NOTICE: IF THE PCM FAILS TO PROGRAM THE TDC OFFSET, DO THE FOLLOWING:

- CHECK ALL PCM CONNECTIONS. - CHECK TECHLINE TERMINAL/EQUIPMENT FOR LATEST SOFTWARE VERSION. - TRY AGAIN TO REPROGRAM THE PCM. IF IT FAILS AGAIN, GO TO PROCEDURE 3.

PROCEDURE 2 - INJECTION PUMP TIMING ADJUSTMENT (SECTION 4)

USE WHEN ONE OF THE FOLLOWING SITUATIONS HAS OCCURRED:

1. **PUMP TIMING** HAS TO BE **VERIFIED** OR **ADJUSTED**. 2. **INJECTION PUMP** HAS BEEN **REMOVED AND REPLACED** WITH **SAME** OR **NEW** PUMP.

A TECH 1 SCAN TOOL MUST BE USED TO CHECK OR ADJUST INJECTION TIMING. ORIGINAL FACTORY TIMING IS MARKED WITH A STATIC TIMING MARK, WHICH COULD BE A CIRCLE OR A LINE SCRIBED ACROSS BOTH THE PUMP MOUNTING FLANGE AND THE FRONT COVER. THIS STATIC TIMING MARK CAN BE USED AS A REFERENCE. IF THE STATIC TIMING MARK IS NOT PRESENT ON THE INJECTION PUMP MOUNTING FLANGE, ONE CAN BE SCRIBED TO FURTHER ASSIST IN HOW FAR THE INJECTION PUMP NEEDS TO BE ROTATED. PROCEED AS FOLLOWS:

1. START AND IDLE ENGINE UNTIL WARM. 2. INSTALL TECH 1 SCAN TOOL. 3. ACTIVATE "TDC TIME SET" IN THE "OUTPUT TEST"/"INJ PUMP" SECTION OF THE TECH 1 SCAN TOOL. REFER TO TECH 1 SCAN TOOL FOR PROPER WAY TO ACTIVATE "OUTPUT TEST."

NOTE: WHEN "TDC TIME SET" IS ACTIVATED, "DESIRED INJ TIM" VALUE IN TECH 1 WILL READ 0.

NOTE: IF ENGINE STALLS DURING "TDC TIME SET" ACTIVATION, SLIGHTLY ROTATE PUMP TOWARD THE DRIVER SIDE OF THE VEHICLE, TIGHTEN MOUNTING NUTS AND REPEAT STEP 3.

4. OBSERVE "MEASURED INJ TIM" FOR CURRENT PUMP TIMING. (REF: "ON VEHICLE SERVICE" SECTION 4 OF THE DRIVEABILITY AND EMISSIONS DIESEL MANUAL FOR TIMING SPECIFICATIONS.) IF A CHANGE IS NECESSARY, SHUT DOWN ENGINE AND LOOSEN INJECTION PUMP MOUNTING NUTS. WITH J 29872, SLIGHTLY ROTATE INJECTION PUMP TOWARD THE DRIVER'S SIDE OF THE VEHICLE TO INCREASE NUMBER OR PASSENGER SIDE TO DECREASE NUMBER, RETIGHTEN MOUNTING NUTS (1MM = APPROXIMATELY 2 DEGREES).

**IMPORTANT** WHILE "MEASURED INJ TIM" CAN ONLY BE OBSERVED WHILE ENGINE IS RUNNING, ENGINE MUST BE SHUT DOWN WHILE INJECTION PUMP IS BEING ADJUSTED TO PREVENT ENGINE DAMAGE.

5. RE-START ENGINE AND OBSERVE "MEASURED INJ TIM" VALUE ON TECH 1 SCAN TOOL. IF IT IS NECESSARY TO READJUST INJECTION TIMING, REPEAT STEPS 3, 4 AND 5 UNTIL CORRECT INJECTION TIMING IS ACHIEVED.

NOTE: IT IS A NORMAL CONDITION FOR "MEASURED INJ TIM" TO FLUCTUATE SLIGHTLY WHILE PCM IS IN SET TIMING MODE.

PROCEDURE 3 - TDC BACKUP PROCEDURE (SECTION 4)

USE **ONLY** WHEN PROCEDURE 1 OR 2 DOES NOT APPLY. ONE OF THE FOLLOWING CONDITIONS USUALLY EXISTS WHEN PROCEDURE 1 OR 2 IS NOT APPLICABLE.

1. THE **FRONT COVER** AND **PCM** HAVE BEEN REMOVED AND REPLACED AT THE SAME TIME.

2. THE **PUMP** AND **PCM** HAVE BEEN REMOVED AND REPLACED AT THE SAME TIME.

3. THE **FRONT COVER** AND/OR **CRANK SENSOR, PUMP** AND **PCM** HAVE BEEN REMOVED AND REPLACED AT THE SAME TIME.

4. THE **FRONT COVER** HAS BEEN REMOVED.

5. TARGET/MR. GOODWRENCH ENGINE INSTALLED.

THIS PROCEDURE USES THE TDC OFFSET LEARN PROCEDURE TO PROVIDE CORRECT "INJECTION PUMP TIMING." PROCEED AS FOLLOWS:

1. START AND IDLE ENGINE UNTIL WARM. 2. INSTALL TECH 1 SCAN TOOL. 3. ACTIVATE "TDC OFFSET LEARN" IN "OUTPUT TEST"/"INJ PUMP" SECTION OF TECH 1 SCAN TOOL.

NOTE: IF ENGINE STALLS DURING TDC OFFSET ACTIVATION, SLIGHTLY ROTATE PUMP TOWARD THE DRIVER SIDE OF THE VEHICLE AND TIGHTEN MOUNTING NUTS AND REPEAT STEP 3.

4. IF THE LEARNED "TDC OFFSET" IS BETWEEN .00 AND -.50 DEGREES, PROCEDURE IS COMPLETE; IF NOT, SLIGHTLY ROTATE PUMP AND RETIGHTEN MOUNTING NUTS. REPEAT STEPS 3 AND 4 UNTIL "TDC OFFSET" VALUE IS BETWEEN .00 AND -.50 DEGREES.

NOTE: TO ACHIEVE A NEGATIVE (-) NUMBER, ROTATE PUMP TOWARD DRIVER SIDE; A POSITIVE (+) NUMBER, ROTATE TOWARD PASSENGER SIDE. 1MM PUMP MOVEMENT = APPROXIMATELY 2 DEGREES.

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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.