in my 89 f150 it will start up and run pretty well, but after driving for 5-30 minutes it will just stall...then it wont start for 5-15 minutes until it cools off.i have replaced the fuel filter and 2 relay switches..after doing this it started and ran and did the same thing...any idea on what this could possibly be?

 

I'll bet your ignition is going dead temporarily. I have had this happen a lot on Fords of this vintage. You can't really test these components because if they are in a live condition when tested, they will test good. If you can get it to run and quit check to see if you have spark through the spark plug wires while cranking the engine after it quits. If you get no spark it's very likely either your coil or the stator in the distributor. You must remove and disassemble the distributor to replace the stator, so try the coil first. Remember you can't effectively test the coil and stator in a case like this. If you test them while in a live state they will test good even though they die and ressurect themselves. Hope this helps.