buddy
Active Member
The IP flange is what bolts up to the timing cover like Bison said, there is a wedge on the timing cover, and thats where I drew the lines on the picture, on the edge of the flange and the wedge tip. If the IP is towards passenger side of the wedge tip then youll have a positive TDCO, and if its towards the drivers side you should have a negative TDCO value, and it shouldnt be very far off of the wedge tip.
When you unplugged the IAT did you observe the IAT value on the scanner go cold? And no change in fuel rate or timing?
And what did you observe for fuel rate and timing with ECT unplugged.
The PCM may not be your problem, but I have found that the trucks dont like sitting down at 5 cam degrees advance at idle. Some even are at 4.5 degrees. Whereas later GM programming has them at 9-11 degrees at idle. I find my IP starts to hunt for the timing when I program it for less than 7 degrees, and at the same RPM fuel rates need to be higher.
When you unplugged the IAT did you observe the IAT value on the scanner go cold? And no change in fuel rate or timing?
And what did you observe for fuel rate and timing with ECT unplugged.
The PCM may not be your problem, but I have found that the trucks dont like sitting down at 5 cam degrees advance at idle. Some even are at 4.5 degrees. Whereas later GM programming has them at 9-11 degrees at idle. I find my IP starts to hunt for the timing when I program it for less than 7 degrees, and at the same RPM fuel rates need to be higher.