5.4L mileage gone bad

[baseball1]

I have a 2000 f250 SD crew cab short box 4x4 with a 5.4L in it. I haven't had this truck very long but I was getting decent mileage for the size of truck. Around 12-13 in town without being hard on the throttle. It's dropped to around 9-10 driving the same. Who has any ideas?
Second part, has anybody tried the acetone for fuel additive and had it work? I found a web site claiming it will if you use 100% acetone. 2-3 mpg better. Thanks for your help.
The truck has 140,000mi on it. Thanks

[fordtrucksonly]

fuel filter may need to be changed, spark plugs, coils, air filter.. have you checked any?

[baseball1]

Yes, did the normal checks, fitlers,plugs didn't do the fuel filter. I looked at the o2 sensors and they are not that old. Could one still be sending a bad signal? What about the cat? I have to do some exhaust work on it, can a bad or plugged up cat affect this? Thanks

[fordtrucksonly]

change the fuel filter and see if it gets better. A clogged cat can cause that but that would be my last option.if an o2 sensor is faulty or relaying wrong info, the check engine light will come on.

[Godofwarmike]

i tried the acetone thing on a car and there was no difference at least noticeable.

did you check the pressure on all your tires? many people overlook this.

have you tried adding some fuel injector cleaner to your tank? clogged injectors make a stream instead of a spray which can lower mpg.

id also check to make sure that none of your brakes are hanging up.

Are you carrying more weight such as a large toolbox with many tools that was recently put in?

[baseball1]

I just changed the fuel filter and filled up the truck so we'll see if that helps. I also added some Lucas fuel additive. I am carrying about 225 lbs of weight for winter but I had that in there b4 the mileage when down. I did have the front hubs locked in for a while so I unlocked them, no change though. I cut open the fuel filter just to see, it was almost black inside. Really bad, it was brownish fuel coming out. Looked like dirty water. Thanks for all the help.

[fordtrucksonly]

The fuel filter was probably the culprit then. Hope it works out for you.

[baseball1]

I just read on another thread that someone said the computer temperature sensor could cause this problem, is this true. Thanks

[70f100]

i just went threw this same prob and it was a o2 sensor. no service engine light came on and took it to autozone and had the code reader put on it showed nothing. it took so long to find out what was wrong the engine burned a valve and i had to replace it try taking it to ford they can tell u exactly what it is even with no service engine light

[rhandwor]

You can get an emission test at a state station. The results will help you out.