GM/Detroit 6.5L ENGINE CONTROLS – TDC Offset Adjustment

Tools Required
• J 41089 Injection Pump Wrench
• J 29872-A Injection Pump Adjustment Tool

Important: Do not perform this procedure when only an injection pump has been replaced (refer to Injection Timing Adjustment).
This procedure should only be used when a DTC has directed you to do so, or one of the following repairs has been performed:
• A DTC 1214 is set.
• The engine has been replaced.
• The front engine cover has been replaced.
• The PCM and the injection pump have been replaced at the same time.
• The crankshaft position sensor has been replaced.
The PCM has the ability to perform a TDC Offset learn when one is not present er has been cleared. This procedure allows the PCM to be updated with the correct TDC offset for the vehicle.
Important: The TDC Offset specification is only to be used after the Learn procedure has been performed.

Learning a TDC Offset
1. One of the above repairs must have been performed, if not, do not continue. Refer to On Vehicle Service for repair that was performed.
2. Install the scan tool.
3. Start the engine.
4. Operate the vehicle until the engine coolant temperature is greater than 77°C (170°F).
5. Clear all DTCs and turn the engine off.
6. Turn the ignition ON with the engine OFF.
7. Hold the accelerator pedal in the wide open throttle position for a minimum of 45 seconds (this step prepares the PCM to activate the offset learn (internal to PCM) and then release pedal.

8. Turn the ignition OFF for 30 seconds. In this step, the PCM powers down (to verify the PCM has powered down, a No Communication With Vehicle screen will display when trying to access a data list.
9. After the PCM has completed the power down, start the engine.
• Verify in the scan tool that ECT is greater than 77°C (170°F). If not, operate vehicle until desired ECT is achieved (vehicle can be driven or throttle can be depressed until correct coolant temperature is achieved).
Important: A new TDC Offset will over write the previous one.
• As soon as ECT is greater than 77°C (170°F) and the engine speed is below 1500 RPMs, the PCM automatically learns a new offset (a momentary stumble in engine rpm will indicate that the TDC Offset has been activated).
10. Check the TDC Offset in the scan tool. The TDC Offset should be between -0.25 and -0.75. If the TDC Offset is within the specified value, the procedure is complete. If not, continue to the next step (adjusting the injection pump).
11. Turn the engine OFF.
12. Loosen injection pump flange nuts using the J 41089 injection pump wrench.
13. Slightly (1 mm equals 2 degrees) rotate the injection pump in the desired direction (use the J 29872-A injection pump adjustment tool to rotate injection pump) and then retighten the injection pump flange nuts (a scribe line across the pump flange and cover can be used as a reference (1 mm equals 2 degrees) which is the approximate width of a scribe line).

Important: In order to achieve a negative (-) TDC Offset number rotate the pump towards the drivers side of the vehicle.
In order to achieve a positive (+) TDC Offset number rotate the pump towards the passenger side of the vehicle.
14. Repeat steps 3 through 13 until the correct TDC Offset has been achieved. It is possible that the injection pump may require multiple adjustments to achieve the specified value.
If you are unable to set the correct TDC Offset or the TDC Offset will not learn, check for the following:
14.1. Check to see if coolant temperature is greater than 77°C (170°F).
14.2. Check to make sure the proper time intervals are adhered to for wide open throttle and PCM power down.
14.3. Check all PCM and injection timing stepper motor connections and for DTCs.
14.4. Check the Techline terminal/equipment for the latest software version.
14.5. Check for proper base installation of the injection pump (injection pump ESO solenoid should be approximately straight up and down).

14.6. If the TDC Offset is stuck on a high + (plus) value, check for a damaged camshaft driven gear key.
14.7. If the TDC Offset is stuck on a high – (negative) value, check for a damaged or improperly installed crankshaft position sensor.
14.8. If all checks have been performed, the injection pump may be malfunctioning, however, this is an extremely unlikely failure.


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