I have a 1992 F150 with 4.9L, automatic, 4X4. The first problem I had was that my PCM burnt up one morning, which I replaced with one from Advance auto parts. That brings a new problem. On some mornings, and some afternoons after the truck has sat, the truck will not start. I turn the key to the on position, the fuel pump comes on and STAYS on. As long as the fuel pump is running, the truck will not start. As soon as the pump switches off, the truck fires right up. This is on random mornings, 2 or 3 days a week when the truck is cold. I've checked the relays and they are fine. I've replaced the coolant sensor to get rid of a Check Engine Light. No check engine light comes on. Truck runs fine once it's started. I would blame the computer if the problem wasn't so random, and if it didn't only happen in the morning. Any thoughts?

 

Check Fuel pressure at the rail, when running & when it won't.