I have a 2000 Ford f150 crew cab 4x4 5.4L automatic. I have 315/75/16 Bfg At and I swapped my stock gear to a 4.56 open.
I tow a 12x7 enclosed lawn trailer about 50 miles per week. I am only getting around 280 miles per tank tops. Usually lower than that. I have a 25 gallon tank. So at the most I get 11.2 mpg.

Is that normal?

 

Well, mileage is really never consistent from truck to truck and driver to driver.

That said, you need to make sure your PCM is programmed correctly for your tire size and gear ratio. I know there are some websites around that will calculate all that for you, but I cant seem to find one right now.
But I have a sneaking hunch this may be your problem...you just simply arent reading the correct amount of miles on your odometer due to the tires and gears.

What gears did you have stock? I think most of the supercrews came with 3.73 LS?

You can ask your dealer to flash your PCM with the right specs for them, or you can buy a programmer yourself (check out the chips section of the forums).

 

like john said get a programer i went with heperteck you can change all the stuff you nned to, tire size, gear rat., tranny shift, and get some horspower, i dont think you will get any mpg tho, my truck with the bellow listed mods gets 10 to 11 mpg on premiem gas, hope this helps

 

You have a 25 gallon tank, but how much are you actually putting in it? I too have a 25 or 26 gallon tank, but when I'm @ about 1/8 tank, I fill up and can rarely get more than 20 gallons in it.

If you had 3.55 gears originally, your 4.56s are 1.28 X lower than original. If you had 265/75/16s originally, your tires are 1.12 x taller than original. You have over-geared for the computer settings.

I agree with John and Big. Get the computer "happy" with the tires and gears and KEEP YOUR FOOT OUT OF IT! The Best you are going to get is 14-15 mpg...may as well just get used to it.

Sidewinder

 

I do have a programmer and I set the gear to 3.56 and the tire height to 34 because that is what the tire actually measured. Im pretty sure my speedo is close to what it should be. I do put into the equation how much I actually fill the tank. 280 miles is what I can get if I do put 25 gallons in the tank. Anyway, I appreciate the info from you guys. I will probably double check everything again just to make sure.

Thanks!

 

The first thing you need to do is calculate your gas mileage correctly. You may have a 25 gallon tank, but you are not putting in 25 gallons each time unless you run the tank dry.(bad idea)

Also with the 5.4 and those big heavy tires, and lots of gear to turn them I would look for you to do no better than 12 mpg.

 

Your mileage sounds normal. Miles per tank is worthless becuase everyone fills up at different places on the fuel gauge. I have a 03 Screw with 5.4L, 4x4, 3.73, 285/70R17 tires and only get 11-12mpg.

 

your mpg is normal