Mustang will not always start after warm!!!! Anyone PLEASE HELP!!!!!!

Here's the prob. Did a 4cyl to V8 conversion a year and a half ago and the car has been perfect up until about 5 months ago. When you start the car when its cold and let it run for about 5 minutes, then shut it off and go to start it again it will stumble for a second then die and when you try to start it again all that it does is crank. Sometimes if I stomp on the gas repeatedly while cranking it, it will start, and it doesn't always do it but generally it does. I've replaced the Ignition module twice, Coil, Distributor, TPS sensor and have checked fuel pressure (has 40psi), spark, grounds and almost everything else I can think of!!!! So now I took it to a shop and they said that my computer is bad (not getting the correct pulse for the injectors)! Has anybody heard of this problem????????Tired of throwing money into it!!! Wondering if anyone's got some advice to what it may be? I've heard of this problem before but wasn't ever able to find out the cause!!!! So anyone who can help shine some light on the subject I would greatly appriciate it!!!!!!!!!!!!!!!!

If the computer is bad, you can reset it by disconnecting the battery for 15 minutes. However, it seems that the spark timing is not matching the timing of the fuel delivery.

Have you checked the egr valve or sensor?

I have a Hayes Repair Manual and it says...
1.Your choke could be sticking in a closed position ( is it SEFI or carburated?)
2.Carbuertor flooded
3.Air filter clogged
4.Fuel not reaching the carburetor or fuel injector (s).
5.Corroded electrical leads at the battery
6. Bad engine ground
7. Starter worn
8. Corroded electrical leads at the fuel injector (s)

but it doesnt say anything about an computer...... i dont know...hoped that helped any.

I have a Hayes Repair Manual and it says...


I'm running the scenario in my head and I have a feeling that it is related to an emissions problem. When starting the engine cold, the O2 sensor is cold and allows the engine to operate on its own accord. But as the 02 sensor heats up, it begins to intervene. I also agree with HighFlow5 0 in that it may be an Exhaust Gas Recirculation problem.
However, since 90Stangjc was considerate enough to look up the problem in a technical manual ( cheater! ) I would start with his list first.

Hey hey, lol. You guys got the knowledge in your heads, i'm still trying to learn from the stupid manual lol.

Hands on experence helps a little too! I've had a few cars where the EGR went bad. Runs great when cold, but like ass when warmed up to proper operating temp.