Just picked up a 1990 f250 with a 351w. I test drove it and it ran fine, drove it home (about 35 miles). When I drove it next it started up and ran fine, tried to start it again but it just kept trying to crank but nothing, no spark. Hooked up a spark tester and tried cranking it, no spark until I turned the key back, like it was discharging or something. I replaced the ignition coil and it's still doing the same thing. Maybe a relay problem? It seems like something gets hot and it doesn't wanna start. Any help? I'd appreciate it greatly.

 

This sounds to me like either the DS2 module under the hood (has two circuits - one for START,
the other for RUN) or the ignition switch on the column. Take your DS2 module to an auto parts
store and have it tested.

 

Is this truck fuel injected?

 

Yeah it's efi.

 

If it's EFI, you might see what the computer has to say, instructions at fordfuelinjection.com

 

Yeah I'm gonna try the self test in a couple minutes.