After replacing the ignition and a new key, the engine turns over but does not start. Could it still be the vats system? The Chevy dealer says no, that if the engine turns over it should start. Can't here the fuel pump working, so is it the pimp or could it still go back to the vats system?

 

My 86 is a little different from yours AFAIK but being no one has responded I'll toss out a thought or two. When you changed out the key and switch, did you use the same resistor type key (assuming yours has that)? IIRC from what I read, the ecm records that value when the car is started the first time and does not change. If it was mine, I'd get one of the VATs bypass plugs that matches the original key value and plug that into the wiring in place of the wire from the switch and give it a try. If it does not change your no-start then it's a fair guess it's not VATs related.
I'm guessing here, but the fuel pump would have to have some way to initialize when you turn the key on but whether that's through the vats or ecm I don't know.
Best suggestion is get out your FCM (You do have one don't you?) and go through the troubleshooting section. Just thought of one more area. Check the fuse for the fuel pump and is there a reset button on yours? I had a Malibu that it popped on once and wasn't running.

Just some thoughts. Good luck

 

Measure the resistance of your old key. Buy a resistor to match. Wire in line from the ignition switch. This wire is under the steering column. The fuel pump is disabled by VATS. I hate the VATS system to many problems as the car ages. BYPASS

 

I've got a '92 LT-1 which sometimes will not start, especially when warmed up. The engine turns once and seems to start, but shuts right off. After some time passes, anywhere from 10 seconds to 5 minutes, it will start right up. It also displays both the security and sys lights at 15 second intervals.
Could this also be the vats or something else? If so, how do I go about by-passing it? Thanks!

 

Far as I know, if you get any attempt to start then vats is not the culprit. Best suggestion is check out this in your FSM (assuming you have one for your car) and see where that takes you.