I have a 98 F150 with the 4.2 motor. I haven't own this truck very long. When you start it up first thing in the morning, it runs fine. If you drive it 20 to 30 miles like I do just to go to town, after I shut it off and go into the store or what ever. I go to start it again and 75% of the time it starts and dies. If you start it and give it some gas to keep it running after about 5 minutes of so the motor smooths out and you can take off. Sometimes I can smell fuel also. One thing that I noticed was I had a nice dual exhaust system put on it with chrome tips. After a few days I noticed the tips and the outside of them were black and full of suite. Any help here on what I should check? Thanks

 

Measure fuel pressure with a gauge at the test port.
Running should see between 30-45 psi.
With hose off the regulator, the pressure should rise 40-50.
If you see above 50 at anytime and there is no change with the hose on or off, the regulator is faulty.
If you see gas in the hose to the regulator, it's bad.
Good luck.