Home » GM 6.5 » GM/Detroit 6.5L – Engine Management – TIMING CONTROL – TIMING ADJUSTMENT PROCEDURES


Timing on the 6.5L EFI diesel is dependent on three variables:
1. Injection pump position, as indicated by the cam sensor and disc
2. TDC Offset (i.e. crankshaft position sensor)
3. The PCM’s learned values for injection pump timing and TDC Offset

Adjusting Injection Timing
When a new injection pump is installed, pump timing must be set. Original factory timing is marked with a dynamic timing mark, which is a circle scribed across both the pump flange and front housing. For engine timing service procedures, a Tech 1 scan tool must be used — not the timing marks.

To adjust injection pump timing:
1. Install the injection pump and tighten the 15mm pump retaining nuts.
2. Run the engine to operating temperature.
3. Connect the Tech 1 and perform “TDC Time Set”:
a. Enter vehicle information necessary to get to the MODE menu.
b. Select F4: MISC TESTS from the MODE menu.
d. Select FO: INJ PUMP
e. Select F1: TDC TIME SET. This option will drive the stepper motor to the maximum
retard position. Use the Up Arrow key to initiate stepper motor action; use the Down
Arrow key to stop action.
f. Note the timing as indicated on the Tech 1 screen (“Measured Injection Timing”). It should be within Service Manual specifications (see section 4 of Driveability and Emis­ sions manual). If timing is not within specfications:
• turn the engine “OFF”
• loosen the pump retaining nuts
• adjust the pump position. Move the top of the pump, using tool J 29872, toward the
driver’s side to advance timing or toward the passenger’s side to retard timing.
• tighten the pump retaining nuts and restart the engine
• perform the “TDC Time Set” procedure as described in step 3 above, as necessary,
until timing is within specifications

Failure to properly set pump timing within specifications will result in DTC 88, “TDC Offset Error.”

Programming TDC Offset

If the PCM is replaced, or if a new front cover, timing gears, timing chain, crankshaft position sensor, crankshaft or other component(s) affecting timing are removed or replaced, TDC Offset must be reprogrammed into the PCM.

To reprogram TDC Offset into the PCM:
1. Make sure the vehicle battery is fully charged.
2. The engine must be at idle.
3. The vehicle must be at operating temperature.
4. Connect the Tech 1 scan tool.
5. Select FO: OUTPUT TESTS from the Miscellaneous Tests menu.
6. Select FO: INJ PUMP.
7. Select TDC LEARN.
8. Start the engine and push the Up Arrow key. The PCM will learn the engine’s top dead center offset value. This takes about 20 seconds.

Failure to correctly program TDC Offset will result in DTC 88.
DTC 88 — “TDC Offset Error”
DTC 88 sets when TDC Offset is greater than +2.0°. This code also sets when a new PCM is installed.


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