pmv

about two days after filling light goes out until next time fuel drops to half.

thoughts?

my GUESS is bad gas cap....

Concordmoose

Could be cap but you might check the vac lines that run to tank and make sure there is no air going into tank after fuel level gets low.

vesmcd

Dredging up an old topic because I'm having the same problem with my '04 with the 5.4Triton engine. Does anybody know if pmv got his problem sorted out?

Thanks.

Rick's 06

If the CEL comes on there should be a code to go with it. I can't imagine what code would be tricked into coming on when the tank is half full but it's a starting point.

techrep

iTrader: (1)

What is the DTC ?? Evap/emission could be a gas cap

Mod (Ret.)

Gas cap would be a first line of diagnosis, the next would be the charcoal canister or its lines from the gas fill neck to it, or from the canister to the engine.

Never, never "top off" the gas when fueling. It causes overflow gas to enter this charcoal canister, and that eventually distroys it, and sets a code. Had this happen to me on a 2005 F150.

vesmcd

I had Autozone check the code but I didn't write it down. It had something to do with the #2 bank o-sensor. Next time the CEL comes on, I will hook my laptop up see exactly what the code is. In the meantime I will go by the local inspection station and have the gas cap checked.Didn't think about not topping off the tank on fill-up. I have been guilty of that

Fbcoach

Was it P0430? If it is I had that code as well. Means that the bank is running lean. Could be a clogged cat, bad o2 sensor, or exhaust leak.

With that said, I ran some SeaFoam through my intake line. It smoked for about 20 minutes from the tail pipe and has run great after that. Try that. If not, I'd see if you can get a diagnostics check.

vesmcd

OK, I ran the tank almost empty and no CEL this time,so I guess I'll have to wait and see what happens next