I am the original owner of an all stock 96 4.0 auto 2WD. I drive 20 miles home from work then let the truck sit 10 minutes and go to leave again. It cranks great but idles very rough. I drive away and it seems to smooth right out. It has been doing this for a long time. Now it has gotten worse. Yesterday I got about a mile from home when the motor lost power and I coasted to a stop. I shut it off since it was running real bad and would not rev up in neutral. It would crank but not really run. I waited like 15 minutes and no change. I waited an hour with the hood raised and then it ran fine back home. Seems to me like a heat soak issue. Which parts are most prone to that? Truck has 203k on it and I never changed fuel filter so I am doing that today. Anyone ever see this before?
Today I replaced the coil but it still does it. I need a fuel pressure gauge... My next thought is the ECM. Anybody have experience using a ECM from the junk yard? The local place has many explorers... Would one of those from the same year work?
I know of a lot of Pre 2000 Fords that do exactly what you're saying. Do you hear the fuel pump running during this (I know you probably haven't paid much attention.) I've had success with replacing the fuel pump relay's on a couple of trucks, including my own.
Finally got a fuel pressure gauge. With engine not running and after cycling key three times it was only 31 psi. Ten when I started it it dropped to 28. Dropped three pounds so maybe regulator is ok. Pressure and drop seem to both be on the low side from what I have read. This was with engine cold. In the morning after I drive to work I am going to test again. Any thoughts at this point?
Fuel Pump Issue usually - Turn key to on and wait to hear the pump engage, wait a few seconds and turn it over, if it keeps cranking, you could always do what I do, kick the gas pedal like you are angry at it and it should start