Chevrolet Truck

Hey there,

I'm working on a 1994 Chevy 1500 with a 5.7 TBI here's the deal it's my friends truck he has put all kinds of money in to it new motor all kinds of new controls the problem is this when the timing is set at o top dead center the motor sounds good when you plug in the ign. Bypass wire it will hardly run I hooked up to my scanner no codes I tested all input controls and dist. And all test good checked all wires plugs you name it I double checked it I swapped pcm with one I had but used the original prom same problem so here's the question does the prom control timing advance could the prom be the culprit?
Jim cameron
October 16, 2007.

The computer controls the ignition timing. When the ignition bypass wire is disconnected the PCM is not controlling the timing this is where you set timing then afterwards the computer takes over.

When you guys are adjusting the timing did you jumper the diagnostic connector A to B.

Oct 20, 2007.
No should I i have never had to do this before

Jim cameron
Oct 20, 2007.