Won't spark until i let off the key??

[BlackFox5.0]

My friends car had the SAME problem. And sometimes it would start then die after a bit. It turned out to be the hall sensor in the distributor. I swapped out his for one from my spare engine, and it ran like it should. So My guess is the hall sensor in the dizzy, which would be easier to replace the enitre dizzy because it's a pain in the ass to change the hall sensor.

 

[Blk91stang]

I guess a lot of things can cause this same problem. One person fixed it by replacing the distributer and another fixed it by wiring a seperate ignition switch. I have done both with no luck... seems like there are tons of possibilities. I think my new msd box and timing control fixed mine.