My truck: 2004 F250 SD 5.4L 191k auto lifted 3" 315/75/16 tires 3.73 rear. When I got the truck with 149k it got between 12.5-13.5 in town and 15.5-16.5 long hwy trips. Also the truck could get up and go no problems. Would easily go up hills without kicking down gears and shooting up in the rpms. Been pulling a 32ft trailer last two years and was getting between 6-8.5 mpg pulling it. The Truck is now slow to move up hill even when not towing, kicks down a lot and is getting horrible mileage. I could get 370 miles on a tank before, now I get 226 miles to a tank. Getting around 8.7-9.5 mpg in town and 10.8 hwy.

Two months ago I blew two plugs and had that repaired. (Gas mileage was falling before that happened and didn't change after it got fixed.)

Recently changed fuel filter, plugs, air filter and oil. Visually inspected MAF and I can't see any build up on it. Looks really clean.

So here is my questions... What else can I do to fix the gas issue. I am thinking about going down to a 285 or 295 series tire, but don't want the truck to look goofy with small tires on. 3" lift. So what else? Someone said maybe the cat was starting to clog, but wouldn't that throw codes? Would a true cold air intake help the performance?

Thanks for the help....

 

Bump... For a response!

 

On my 2006 F350 5.4l, i had new cats put on, new plugs/coils, and ethanol treatment in the gas to fix the terrible sputtering and lack of power. The new plugs made the most differnce. The ethanol treatment also made a noticable difference. It's a secondary truck thst I use mainly for plowing, so I put 93 octane gas in it because that is the only ethanol free gas close to me.

Haven't had any issues since doing all of that. Only have about 62,000 miles on it.

Added a 5 Star tuner last summer, which added more pep to it.

 

Update: replaced plugged cat. Performance feels good but truck is still only getting 5-7mpg around town. Not driving it hard. Could lazy 02 sensors be the problem? Not sure what else is left to look at.

 

has the throttle body been cleaned..?

and the computer reset after the cat were replaced???
fuel injector cleaner? "Techtron" only

 

No the throttle body hasn't been cleaned but the maf sensor looks clean. Ford dealer said no way to reset and it wouldn't do anything to computer to reset it. Also I have not tried any injector cleaner

 

to reset the computer.. remove the negative battery cable for 10 minutes... and reconnect.. computer has to reset... memory has dumped.

 

Even if I had no check engine light before?

 

it not for the check engine light..

the computer adjusts itself based on many sensors...
after a sensor or catalytic converter replacement. the computer should be reset back to the beginning.. and it will relearn and adjust itself to New parts...

 

I'll give that a shot. Thanks