TDC Offset?

[Big T]

Son got this reading from the GM Tech Scan:



I thought the desired was -1.91. Or is it -1.94?

 

[ak diesel driver]

-1.94 is for max performance. Stock is -.35 to -.75 IIRC

 

[MrMarty51]

I messed with the timing on My truck several times. I was shooting for around -1.20 or so. I finally give it up when I got it to -1.43 or so. It starts good, runs good and I think gets a tad better fuel mileage than it did when it was at -.43.
I followed AKs pattern and made an IP wrench using the box end from a reversible 15mm gear wrench and fabbing a handle for it to suit the need.
It aint perfect but it does work quite well.

 

[Big T]

That's the TDC Offset that Colby hit installing the IP.....then checking it on the Tech II.

 

[denata]

There are three parameters:
Desired angle
Current angle
Defolt offset.

For example:

 

[denata]

Disired and
Actual timing

 

[denata]

For IPi used Jonnesway W6511517.

 

[ak diesel driver]

Did Colby actually do a relearn or just read what it said? The PCM stores that value and it won't change unless a relearn is done.

 

[Big T]

Did Colby actually do a relearn or just read what it said? The PCM stores that value and it won't change unless a relearn is done.

Probably this ^^^

 

[THEFERMANATOR]

Did Colby actually do a relearn or just read what it said? The PCM stores that value and it won't change unless a relearn is done.

Not always true. I just set red97's for him. It was at -.88 with his old pump, it went to -2.46 and set a resistor error when he installed his new pump WITHOUT telling it to do a relearn. So they CAN relearn on there own(seen it with my own eyes).

 

[THEFERMANATOR]

Disired and
Actual timing
View attachment 67424

Desired and actual timing is generally checked while doing a timeset, and time set is only required on OBD1, obd2 can go straight to a tdc offset relearn(but doing a timeset can come in handy when trying to dial in your tdc offset to see how close you are to hitting the magic 3.5 degrees).

 

[ak diesel driver]

His is an obd1 so maybe that's the difference

 

[Big T]

His is an obd1 so maybe that's the difference

He said that was likely the prior reading in the Tech Ii. Also, the truck is running great right now, so he will leave it alone. We’ll deal with TDCO after installing the AC Delco IP during Thanksgiving week. AC Delco IP will arrive this week.

 

[Husker6.5]

@Big T Oh goody! Looks like you'll be carving up a big turkey this Thanksgiving!