TPS will not read 100%, only reading 60% (3.0V) at WOT

[Time2Kill]

I've been fighting this for a couple days now and was hoping I could get some help on here.

I'm helping a friend setup a LQ9/4L80E combo (with a Gen3/LS1 PCM) in a 1982 K10 Chevy and we're having problems tuning it because the TPS will only read 60% to 65% at wide open throttle. The throttle body is opening all the way. I also tested a completely different throttle body with different sensors with the same results. I have also tested the second throttle body on a 1999 Firebird and it reads 100% for WOT so I know its not a sensor issue.

On the K10, the TPS reads about .85v idle/closed and only 3.0~3.15v at WOT. This is with the truck key on engine off and also key on engine running. I have verified that grey wire on the TPS sensor is receiving 5.0V and have also tested all the wires for high resistance (all under 0.02ohm) and none of the wires are shorting to ground.

I have also checked the 4 PCM grounds (Pin 1 & Pin 40 on each connector) and they are about 0.5ohm to ground on the body, frame, engine, or battery negative. I have also moved the grounds and made sure everything was nice and shiny were they are connected with no changes at all to the TPS reading. I have also tried reflashing the PCM to a couple different tunes with complete rewrites.

My only other concern when I was checking grounds, Pin 4 from the OBDII connector kept sparking. I have Pin 4 & Pin 5 on the OBDII connector sharing the same ground as the PCM grounds. When I was moving the grounds, Pin 4 on the OBDII kept sparking everytime I moved it. When HPTuners is plugged in, Pin 4 becomes hot. This doesn't seem right to me but if I don't put Pin 4 to ground, HPTuners will not read the PCM. I also moved the OBDII grounds to the other side of the vehicle away from the PCM grounds with no changes to the TPS reading.

This LQ9 swap was in a Crown Victoria right before the K10 using the exact same PCM and wire harness with 0 issues, so I'm at a loss. The only thing that was changed from the Crown Victoria to the K10 was the addition of a 4L80E trans, we were running a TH400 in the Crown Vic.

If anyone has any ideas, I would GREATLY appreciate it as I can't think of anything else to try. I brought the PCM home with me and I'm going to test it in another vehicle tomorrow to make sure there isn't something wrong with the PCM itself.

[gagliano7]

Sound like a wiring problem. You must have a short somewhere.