You could ground out the signal wires and see if the PCM shows a voltage below 0.35 volts. This would prove the wiring and the function of the PCM.

Short the black to the tan/white and to the purple/white wires.

Remember when it's disconnected it should show 0.45.

 

so whaaaat? signal wires as in unplug the 4 weatherpacks in the pcm. i would assume the pcm is working fine since it did this on 2 pcms, this one being a new GM piece. i guess i need a step by step. but, here's what i know...car runs great in open loop. fuel trims cut out in closed loop. logically thinking, i need to look at all the items that determine short term fuel trim in closed loop. so what is most important???

 

It seems to test your harness out past the PCM will have to be done via voltmeter. I hate wires man, but trying to lead you in the right direction. Sometimes things can get melted by headers etc.

 

i have a feeling its something like that. i was out rompin on it for a half hour straight and the next day it started acting up. I'm hoping its something as simple as a burnt wire, or something.... u have a schematic of the power wire into the pcm?