95 LT1 Erratic voltages EEhack

[Opti]

I just swapped a 96 Camaro to an obd1 pcm so I can use EEhack and Tunerpro. I was doing a quick datalog, and wanted to do a power balance test. The power balance test wont run because the TPS voltage is bouncing erratically from .4 to .8 which is in the acceptable range, but it thinks there is constantly fluctuating throttle between 0-4%. I noticed multiple other sensor bouncing erratically. I know 3 or 4 of them share a pcm ground.
My first assumption is a ground issue on the car, but before i go hunting and checking all the grounds wanted to see if it may be a signal issue, or if someone had run into this before.
Also the laptop was not plugged into a power source.

[steveo]

pull the belt and try again to prove your alternator rectifier isnt shot.
the tps should be dead on consistent
if it still does it, you have a shoddy ground, or maybe extreme rfi from an arcing plug wire or something?

[Opti]

pull the belt and try again to prove your alternator rectifier isnt shot.
the tps should be dead on consistent
if it still does it, you have a shoddy ground, or maybe extreme rfi from an arcing plug wire or something?

Thanks I'll try that

[Opti]

I pulled the alternator and its connectors. No change.

So the issue is I have erratic signal from many sensors. The obvious ones are map, tps, a/c pressure, ect, iat and ac evap temp. It will even do it with key on engine off. They dont swing far but swing a couple degrees or percentages always. I noticed the negative battery terminal was a little loose. I tightened it up and it helped a little. I checked the main lug on pass side strut tower and cleaned it up, I found a couple broken grounds at the coil. I may have broken them though in dissassembly. Im going to repair those grounds, but even with them off, I still get the erratic signals.
I also unplugged pretty much every sensor or actuator I could find and checked one at a time to see if something was backfeeding. No change. In fact when the erratic sensors are unplugged they remain erratic, just at a different reading.

Didnt have time to get under car and check the grounds on the bottom. Will do that when I repair the grounds on the coil.
Also havent check for an arcing plug wire, I will but I think it might be unlikely because the wires are relatively new and the vehicle runs very well.
Anything else to check out when I get back to it?

[NomakeWan]

Sounds like the reference ground for the PCM itself is floating if unplugging the sensors doesn't resolve the fluctuation.

[Opti]

Thats what Ive figured but the PCM ground is accessible from under the car, and I worked in the rain as long as I could stand. Waiting for a dry day to get under it.