I just bought a 2000 F250 4x4 with a 5.4/Auto. The truck has been sitting for awhile and started every couple months according to the previous owner. When I got the truck up & running to give it a test drive, there was very little fuel in it, so I was really hoping I wouldn't run into too many old/bad fuel problems. I poured in a bottle of Lucas, a bottle of HEET, and about 7gal of 93 octane for that first trip through the backroads near our house. It ran like garbage for awhile but cleared out over the time we drove it that day. Couple weeks later, I went out to pay the guy and drive it home to start getting it roadworthy. That was the first time I experienced the following issue...

Long story short, I think the fuel is a bigger problem than my optimism predicted. Two fuel filters, an air filter, and a couple fill-ups with 93 octane & more fuel treatments, and I'm still having this issue: The truck can't make up its mind how it wants to run. Hot or cold doesn't really matter, because it goes through all of its mood swings at different times no matter how long it's been running. One minute it's clear and running fine, then the next it's spitting & sputtering, will barely pull itself, and has even died a few times. If you hold about 1/4 throttle for a few hundred feet, it'll clear itself out and start running fine again-Sometimes for 30-45 minutes of driving, and sometimes for 30-45 seconds lol.

I do have a CEL and having it scanned did give me a trouble code. I don't remember the number, but the general description was that the "lack of a heated O2 sensor was causing a lean condition". The sensor is present and plugged in, but the wires have been spliced in at some point with butt connectors. Would the two (CEL and running crummy) be related, or is it likely this is just a case of bad or weak fuel that will either have to work itself out or remove/clean or replace the tank and the sensor needs to be replaced just to clear the CEL? He did put a new fuel pump in it last year, and I plan to do a pressure check this weekend as soon as I can get to my Dad's to borrow his tester.

I do know for a fact that my problem isn't a clogged converter, as I had the entire exhaust system replaced front to back yesterday and the problem is still present. I didn't think that was going to solve it, but the truck sounded so TERRIBLE that I couldn't tell a dang thing when I was driving it....

 

well...it would be better if you could recheck the codes and post them. with actual code/s might help point you in the correct direction.

Off hand...
Double check those wires make sure they have a solid connections for the O2's and for the fuel pump. Considering that it has sat for some time, whole sale change the relays for the ignition and fuel delivery. Little rodents have a way of infesting chewing on wires.

I would check for vacuum leaks...main culprit can be the elbow on the rear of the intake from the PCV....but look everything over. Maybe remove the throttle body housing and clean it and while it is off, remove and clean the IAC.

With 3 fresh tanks now run through, doubt it is fuel related...but checking fuel pressure can't hurt.

Have you changed the spark plugs yet? It maybe a bad plug...or a boot intermittently shorting out or a bad COP?

You could really benefit from a code reader that can see live data and maybe freeze frame...(mode 6) and count the miss fires & hesitations as it happens.

 

Check the PCV system for leaking or collapse rubber hoses or that rubber elbow around back facing the firewall.

You probably have a gross vacuum leak.