Well we've had the 250 for about a year or so now... it's a 2008 f-250 super duty has the 5.4 v8, XLT, supercab, 4x4, and it is a very sharp looking truck... When it was bone stock, we were getting around 13-14 mpg, not bad at all for a 250.... however we have since added a ARE cap on to it and put some tools and materials inside, maybe a total of 400-500 lbs total of tools and what not... not loaded heavy at all... For the first couple months we did not notice that the gas millage dropped... but i just lately drove it ( it's dad's work truck) and it completely lacks power, even on level ground...
i beleive it has the 3.76 LS axle..

Now it has 23,000 miles, basic oil changes done every 4k miles and what not, proper air in tires, the truck is not beat on what so ever... But just cruising on the highway, we are now struggling to get 8 or 9... It keeps poping in and out of 4th OD to 4th unlocked and with some not very steep hills, it needs to go into 3rd and get to 4000 rpms to stop from dropping past 50...

We own a 350, same engine, reg cab, 4x4 and it has a 9' box on it and it loaded HEAVY.. it gets 13, and has plenty of power yet, it stays in 4th gear locked like it should and just cruises... the 250 will not cruise at low throttle input, if you try to drive like i do with my 150 (5.4 also) and just barely touch the gas and remain at 55- 60 mph, this truck will slow down to 40 and fight to keep it at that...

what could it be... The cap is very thin aluminum, and truck is barely loaded, a ladder or two, a small toolbox you can take with you, and some materials of 300 lbs or so...

Could it be the stock fuel filter? or a dirty air filter?
I went to check the air filter and saw that the straps to close it were all un buckled and i couldnt open it easily.. it is 15* with strong VERY cold winds so i said screw it and ran inside... am i on the right track, or do you think it is just the cap and we didnt realize it for the past 6 months that we have had the cap?

8 or so MPG is killing us as we are electricians and drive everywhere for a living... getting only 250 miles from a tank and having the gas light come on at 1/4 tank is ridiculous..

It feels as if we are towing a 4000 lb trailer everywhere we go, and when we tow, it feels no different, no *****.... the 350 has 2x the power and 2x the weight on it...

what can i do to fix it... can't sell the truck for a hybrid... need to keep this thing till it is paid off and then a lot more... it is here to stay.

 

didnt know they made the 350 with a 5.4

 

Yep... sad. I once had a job where I had to drive over long distances a 1989 Ford E-350 15 passenger van with the I6 300. It could not get out of it's own way.

On a side note, a buddy of mine used to drive a 2001 F-250 regular cab with the 5.4 for work and his Dad has a 1999 Silverado 2500 extended cab for work with the 6.0 gasser. Neither truck got good gas mileage.

 

:o That is absolutely criminal! Did the engineers that gave the O.K. to put that engine in that van ever drive the thing??? I had an E-250 back in about '88 that had the I6-300. I stole the thing (belonged to a large co. that only put a little over 30k mi. on in the 3 yr. lease) for $2200. Was in beautiful shape. Had it about a year and sold it for $2800., but I felt guilty about selling it to him even though the price was good because that thing wouldn't get out of it's own way, and boy did it burn a bunch of fuel trying to get out of it's own way. Took at least 3/4 throttle to maintain 60 MPH. They had installed a huge vacuum gauge up on the dash and that thing showed about 6 in. of vacuum at 60 MPH because of the heavy throttle on level ground. (see 1st sentence)

 

it's the base motor for all super duty trucks

 

when is the last time you changed the air filter??? and are you using motorcraft oil filters???

 

napa gold oil filters, use them in all of our vehicles and never had an issue... the air filter i am not 100% sure was ever replaced, but my dad swears he did it at around 15k....

could a dirty air filter cause this?

 

Air and fuel filters can certainly cause this - as could a clogged cat.

 

If it's never been back to the dealer, it needs to go. The computer needs to have the latest flash installed. It will cure most of the issues but don't expect massive improvements in the fuel mileage. It should get around 12-13 though.

 

I would make a suggestion too. If oyu can afford it, look into a programmer. After the other issues are all set, you might gain 1-2 mpg's or so and the truck would drive better. A quiet si/so exhaust about the same loudness as stock might boost performance and mileage as well.

 

got a new fuel filter installed today, when i was driving around town it felt peppy and would cruise at 30 mph perfectly... i thought i fixed it... then as soon as i got to the highway, and tried going 55-60 it lost it's "oumph" It starts searching gears and the only time i can get it to hold in 4th locked is going down hill, if i let up the gas enough to get it to lock in, i start coasting and the MPH drop pretty quickly...

air filter was new a couple months ago, still looks good...
oil change was done a month ago

i talked to my dad and he also believes that it is only something that happened recently, when the cap was installed we lost 1 or 2 mpg but not 5 or 6...

So i should take it to the dealer for a reflash and hope it fixes it? i doubt it is a clogged cat with only 25000 miles on it... but i've seen weirder things..

 

Any indication that one or more of the brakes are dragging?

If the MAF sensor got dirty, maybe that would cause it to run overly rich.

 

The TSB number 07-14 dated July 8,2007 addresses the exact issues you have for YM 2008 F250 with the 5.4 V8 gas engine. If you haven't had the computer reflashed, you will have the problems as you described. But you have to take it to the dealer for this no cost service.

 

not the f450 and f550

 

alright, labnerd, thanks a lot... hopefully that will cure it and i'll be able to drive this truck without pouring money out the window..

thanks to all for your help also