I know the technical procedure for adjusting the injector pump timing and the offset. First you adjust the pump timing to 3.5 degrees advance. Then you adjust the pump for a -. 25 to -. 75 degree offset. What exactly is going on here? Doesn’t moving the pump to adjust the offset unadjust the original pump advance of 3.5 degrees? The procedure sounds like you are always going to counteract the pump timing when you set the offset. What’s the offset anyway???

Signed,

Confused MFParker in Wayne

OK, there's 3 main elements that need to be observed, but kept seperate, a lot of people mix these things up and get really confused.

TDC Offset, this is the value the ECM calculates which is the timing relationship between the injection pump at full retard and the crank. This is the one your trying to set, the Time Set function is a tool to help you get the pump close enough to relearn a new Offset.

Time Set, this is where everybody gets the magic 3.5* number from. When you perform the time set procedure with ANY scan tool, what this does is command the pump to full retard, and display the ACTual timing of the pump. When you use this, you want to adjust the pump until you get as close as you can to getting 3.5* so when your ECM relearns the TDC Offset you should be in spec.

DES/ACT timing, DESired timing is what the ECM determines the injection pump timing needs to be relative to the crank, depending on engine speed, load, temps and throttle position. THIS HAS NOTHING TO DO WITH TDC OFFSET OR TIME SET. You can't set your DESired timing, thats up to the ECM and it will change constantly as engine demands change. ACTual timing is just displayed to give you a comparison, the ACTual timing should always follow DESired timing closely, this indicates the pumps advance mechanism/stepper motor are working properly.

Boy, that makes the whole procedure make much more sense.
What are the consequences of a timing setting of 12.5 degrees advance? That’s where my pump is now. I’m waiting for the adjusting tool I order from GM to come in so I can turn the pump. I haven’t been running the truck, just wondering if the consequences are anything like over advancing a distributor on a gasser.

What timing setting are you referring to? Thats what you get with the Time Set function??? Thats way too advanced, you'll never be able to relearn a new offset that far out. You will get kicked into limp mode and SES light will come on.

MFP,
Timing & TDC offset are 2 different things as TDG spells out, best done with a T2, I did come up with a way to set it with a MT2500 scan tool but it's difficult to get with it as it is with a T2. In FAQs I listed how I have done it on my truck multiple times, read that if you still have questions list them here. This method only works for OBDII trucks.

I have the AutoTap program with the GM enhacements. It works with my windows lap top. I'm waiting for the J29872 IP wrench I ordered from GM to come in. Has anyone ever used this program to time the IP?

Never tried it...

If you can read TDCO at it's negative value, then the Inj Pump can be timed with that software.

What value TDCO do you get for the +12.5deg Des\Act?

Get a load of this, right now with the timing @ 12.5 degrees advanced, the AutoTap program reads my offset as +5473 degrees advance. I don't get it either. This is one reason I'm questioning whether or not I am getting a good reading. When I finally get the pump turning tool, I'll set the pump to 3.5 degrees advance and see if the offset changes when I command the PCM to reset the offset. Oh, one code, the 2016 timeing circuit one. Expected.

Make sure the CTS on the water crossover is plugged in.