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Old 12-22-2008, 02:35 PM   #1 (permalink)
windrover
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Don't understand GMTDScan IP timing values and adjustment

I just recently replaced my IP using the advice presented in https://www.dieselplace.com/forum/sho...d.php?t=279750
I was very careful to make sure the index pin in the gear hub and the actual position of the new IP was in the same position as the old IP. Everything went smoothly and the truck started up w/out any problems. It sounded pretty smooth.

I then hooked up GMTDScan (Basic) to check the IP timing. The notes provided with the IP stated that IP timing must be set to 3.5degrees. I've also seen that value mentioned in IP timing threads. The values I received with GMTDScan were:
Actual Injection Pump Timing (fluctuates around 31-32 degrees)
Desired Injection Timing (9.9)
Measured Injection Timing (8.9)
TDC Offset (-0.79)
(The engine operating temp was only about 90 degrees when I measured these.)

Questions
1) What is the difference between "Actual Injection Pump Timing" and "Measured Injection Timing" ?
2) Which one relates to the 3.5 degree IP timing mentioned in the notes and posts?
3) The way I understand things, the TDCO is changed by rotating the IP. How do I change the IP timing to meet the 3.5 degree specification? (which I think is supposed to be set before adjusting the TDCO)

I ran into a few threads that mention timing values similar to the ones I have,
(https://www.dieselplace.com/forum/sho...d.php?t=245150)
(https://www.dieselplace.com/forum/sho...d.php?t=213374)
but they didn't clarify anything for me.

I've spent many hours searching and trying to find relevant information, but I can't seem to figure this out (maybe I'm not finding the right threads???).
Can someone help?

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Old 12-22-2008, 02:53 PM   #2 (permalink)
ghitch75
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you need GMTD scantech....payed 1...to set your time the PCM has to learn where the timin' is....just replaced my IP on the burb Wednesday....engine must be above 180f before time can be set... i have mine set at TDC Offset -1.94....little loud at startup but she runs great after warm...

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Old 12-22-2008, 03:10 PM   #3 (permalink)
windrover
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If I understand what you are saying, it is GMTDScan Tech that sets the IP timing to 3.5 degrees. Is the procedure for doing this well documented with the software?

What is the difference between "Actual Injection Pump Timing" and "Measured Injection Timing" ? If the pump needs to be timed at 3.5 degrees and my IP shows "Actual Injection Pump Timing" at ~32 degrees why does the truck run so well?
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Old 12-22-2008, 03:19 PM   #4 (permalink)
ghitch75
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here is what you do....

* Start GMTDScan Tech.
* Connect to your truck.
* Go into the dashboard view and verify that the engine coolant temp is at, or above, 180 F. If not, wait before proceeding.
* Go into the DTC view and verify that no trouble codes are present.
* Go into the TDC view.
* Take note of the current DES/ACT/TDCO values. OEM is +3.5/+3.5/-0.5. For both DES and ACT 7-9 degrees is more normal and acceptable.
* Click the TDC Time Set ON button. DES should now read 0 and ACT should read +3.5 on average.
* Click the TDC Time Set OFF button to go back to normal operating mode.
* Click the TDC Learn ON button. The TDCO value will now fluctuate for about 20-30 seconds before setting itself. You can end the sequense prematurely by clicking the TDC Learn OFF button. The current TDCO value will then be set in the PCM.
* If you are not happy with the TDCO you get you must turn the injection pump. Towards the drivers side is "-" and towards the passenger side is "+". A 1mm move equals 2 so take it very easy and do not attempt to turn the injection pump while the engine is running!
* Repeat the TDC Learn procedure until the TDCO you want is attained.
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Last edited by Freddyack; 09-22-2014 at 07:46 PM. Reason: Correct advance/retard instructions
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Old 12-22-2008, 03:53 PM   #5 (permalink)
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Truck needs to be up to operating temp to set timing. Timing will be advanced when cold. Your desired is what PCM is requesting and the measured I would assume is what it is. Haven't used that software but on scanner the actual is well what it actually is. But if it's running good why mess with a good thing.
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Old 12-22-2008, 03:54 PM   #6 (permalink)
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I'm to slow.what he said
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Old 12-22-2008, 05:07 PM   #7 (permalink)
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I've read the GMTDScan Tech FAQ "what steps do I need to take to set TDCO" before, but didn't (and still don't) really understand the IP Timing to TDCO relationship. I think I do understand however that the software (or scanner) enables the IP timing (and I assume it is relational to the crank position - hence the offset in degrees to TDC for each cylinder injection event).

Nevertheless, I still don't understand the difference between "Actual Injection Pump Timing" and "Measured Injection Timing" - and why there is such a difference in values measured by the GMTDScan Basic software (32 to 9).

One other thing I'm not clear with GMTDScan Basic and IP Timing. If I was to move the IP 1/4mm (right now, before I set the IP timing to 3.5 degrees) towards the drivers side, theoretically, that should decrease my TDCO to about -1.45. Is that what the GMTDScan Basic software would show, or are all changes to TDCO before IP timing irrelevant?
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Old 12-22-2008, 08:14 PM   #8 (permalink)
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Timing is within your chip-computer controlled. What you're setting is TDCO.
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Old 12-23-2008, 08:17 AM   #9 (permalink)
ghitch75
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2x
Quote:
Originally Posted by RCpullerdude View Post
Timing is within your chip-computer controlled. What you're setting is TDCO.
thats why you need scantech....
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Old 12-23-2008, 06:28 PM   #10 (permalink)
RCpullerdude
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Quote:
Originally Posted by ghitch75 View Post
2x
thats why you need scantech....
But it's still only doing TDCO.

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