IP Timing and TDC Offset Learn

[Uncle Wally]

Ok guys,

I'm missing some big picture here. I just spent 2.5 hrs with a Tech1 hooked up to my truck to set the timing and TDC Offset, and I didn't get anywhere.

Let's go back in time a couple weeks. The truck ran great, but was way underpowered. I noticed damaged vanes on the turbo intake side after a trip out east, so the decision to buy a non-wastegated turbo was made. I also purchased a chip from JK (max power). While I was waiting, I sent the exhaust manifolds out to have them coated. I got everything back together, and found that she was a bear to start. I mean really bad. I have to cycle the glows several times to get her to start, and she's rougher than 60 grit sandpaper for the first several minutes.

Here's what I saw:
No Codes - not even an 88 with the new chip
TDC Offset - -1.41
Pulse width - 2.02 ms
Demanded Timing - 4.4
Measured Timing - 4.4

all read with the engine running.

Since the GM Manual is EXTREMELY vague about how to go about this, and the fact that I leant my 2001 & 2002 DP Articles out to a friend and have not recieved them back, I don't think I did what I needed to do (set the timing correctly).

We did try to move the pump a little and I got the TDC Offset to -1.94 (several times in a row - so I'm sure the value was correct) but the demanded timing and measured timing stayed at 4.4. The GM Manual states that that should be at 3.5.

Coming to the conclusion that I yet again know enough to be dangerous, I decided to try and get everything back to where it was (or as close as I could) and ask some questions.

How on earth do ya figure out what order to this and what is required?

I am assuming that the pump timing needs to be set at 3.5 prior to doing the Offset Learn. While it was running, we tried to adjust the pump to 3.5, but had no luck, it stayed at 4.4.

So somewhere in here I am missing the big picture. I'm sure the article on how to do this makes it easy enough that my 10yr old son would understand it, but I won't have that available until late next week at the earliest.

Any comments that could clear up the mud?
Thanks in advance,
Waldo

[ucdavis]

I think you have to rotate the IP w/engine off. Reason- IP reads timing off a rotating disc inside IP housing & adjusts timing by the stepper motor on Rt side of pump (by atually rotating the disc assembly inside the pump by the desired adjustment degrees). If you start engine, it has a reading on what constitutes TDC from the disc. So if you rotate the housing while the disc is rotating, the stepper motor is probably receiving instruction to compensate for the manual rotation. I.e. the IP reader has no fixed reference in that condition so it treats a variable as though the engine created the rotation.
You'll note I said "I think." GM is way smarter than I am (if I forget about AutoPark, and about a dozen other design features of my rig) and might have designed a fixed reference into the plan, and your trouble could be something else, but doing rotation w/engine off, tighten bolts, then recheck timing is easy to do.
Also I coulda sworn I read a warning about loosening IP mount bolts w/engine turning; something about stress on the gear inside. Hope I remember this wrong & you don't have drive gear damage- I'd expect some noise, if that was the case, from the oil filler tube.
Good luck & post your findings.

[Kennedy]

Commanded and actual WILL fluctuate depending on the PCM's mood, but should stay together.. You are set fine, BUT if you wnat to dig in and play/learn, use TIME SET which will command desired to 0

[Uncle Wally]

So all I need to is Use Time Set to get the desired to 0. Then measured will come up as the actual timing (which the manual says should be 3.5) which I can adjust to. Should this not be done while idling? Then set TDC Offset learn at -1.94?

My concern is the fact that she is a total bear to start. I can see going through batteries and a starter quickly like it is now.

Waldo