So I own a 2003 f250 5.4, auto trans, 4x4, extended cab, short bed, my tires are 285/75 16R and 3.73 gears. Ive done all fluid changes spark plugs replaced o2 sensors and put in a high flow y-pipe. I bought it with 100,000 miles and right now I have 106,000 and im only getting 7-8mpg in city and about 11 highway. My question is whats wrong with my truck why is it so bad, what could it be? I could check fuel pressure but whats should it read at idle and throughout the rpm? Is there any other sensors that would effect my mileage? I really have no clue and it would be nice to get over 10 in the city lol

 

Honestly your not that far off the mark of the average for these trucks. The tires aren't helping you gain anything. If you are calculating by hand you are going to be off some because of the tire size as well. A lot of guys say to drive like you have an egg under your gas pedal.

 

Your mpg still seems low to me. I have basically the same truck, same tires and gears but with the V10 and get a good bit better than that. More like 10 city 13.5 highway. The 285s will not throw off the odometer it actually makes it closer to where it should be.

If you did not clean the mass air flow sensor get some CRC mass airflow sensor cleaner and clean it. Also change the fuel filter. Would not hurt to run some Chevron Techron fuel injector cleaner through the truck also.(same stuff as the Motorcraft injector cleaner)

 

I have the same truck but with 35's. My overall average is 10-10.5

You could do a fuel and air filter change... might help a little bit.

 

Same set up as drey and I get roughly 11mpg average. My 35s corrected my speedo so its dead on now.

 

2005 SD 5.4 k&N intake, stock exhaust, 275/70/18 tires, auto trans. 13.4 city, 14 highway (if you belive the ditigal display). I guess I have a light foot during city driving. I actually thought I was getting low gas milage.

 

The 05+ engines are 3v so i think that they get better MPG's, not sure but i know they are the preferred engines over the pre05 2v engines.

 

I'll concur that my 06 F250 averaged 11-12 with mixed driving 70% highway/30% City. Towing and a lot of city driving drained the tank pretty quick. I came from a 2005 F150 5.4 that got 14-15 similar driving and figured it would be near the same in the 250. However the 250 was quite heavier so I got the same mpg of my 150 when it was towing a trailer which probably was a similar weight. I drove the 250 with an "eggshell" under the accelerator.

 

I used to own the same truck with 35s and got around 8 all the time. did not matter city or highway...8 my v-10 does slightly better getting 10 ish in town

you have to remember BIG TRUCK tiny motor. that's y the v-10s get better mileage. the bigger motor is not working as hard to get the truck rolling

now I also have an 08 f-250 with a 6.4 that gets 23 mpg on the highway and 16 in town

 

You bought a 250 with a gas motor in it. Also like others have said your tiny engine is working to get your rig moving.

 

Yup, I'd agree that it's probably the smaller engine on a large truck. Those tires are basically 33 x 11.50, so larger than stock. Since you bought it used, are you sure about the gear ratio? Is it possible that the gears were lowered at some point for better towing performance? That could affect your speedometer, odometer, and gas mileage...

 

Smaller engine don't matter that's still a lot of torque reguardless, my old 94 chevy weighed 100lbs less(still 8,500 lbs) and less power I still averaged out 13 city plus plenty of other people say they get 10+ and that's even lager tires than mine and lower gearing than mine. Ive done filter and fluid too, ive done just about every bit of maintence I can think of. Ill clean MAF and throttle body and see what I come up with. but something still seems wrong

 

Does the truck ever smell funny when you step out of it? You might have a seized caliper (or calipers) that would affect your mileage. Generally you can visually see one or ones that have stuck and heated up. I had one, never really looked at the mileage though, but had smell coming from rear drivers side and definite discoloration, and could feel it when driving.

 

BTW, that is poor mileage. I have a 99 2v 5.4 with similar setup without the mods and get better than that (~10mpg) towing a boat with camper on.

 

You are comparing apples to oranges when your comparing a Ford to a Chevy. Each truck has completely different aerodynamic and body designs. A smaller motor in a truck thats meant to be a 3/4 or 1 ton truck is going to WORK harder to get it moving. While I don't doubt that you might be getting less then "adequate" mileage, it's tough to pin point it. MAF and throttle body might help it. If all else fails, take it to autozone and have them plug in a code reader, and see if your throwing a code that you might not see. Best of luck with your rig and I hope you get it running how you want it.