91 Camaro rs Timing

91 RS with a 3100. Car came into the shop no start. Owner replaced the distributor, I got it running, unplug the timing bypass wire, line timeing up to 10 degrees BTDC, plug the bypass wire back in, and it wont start or stay running without feathering the throttle. Come to find out the computer is retarding the timing. Bypass wire unplugged and you can drive the car around the block fine, plugged in and it wont run. I need help on this one. The owner attempted to fix it himself before bringing it to the shop. He has a used pcm on the floor I swapped out, no change. I'm wondering if he has the wrong prom chip in it. Any suggestions?? I'm at my wits end on this one. I hate when people attempt to fix things on their own before bringing it in.

I'm a liberal shadetree mechanic,but that is another story. lol

It's my understanding, if the bypass wire has voltage on it and white wire has nothing, it won't run. With bypass ignition, it can run off the ignition module, but no spark advance without pcm control.

The signal on the bypass wire, tells the ignition module to use the signal on the white wire for spark timing.