Last night i filled up. Reset trip-o-meter and i noticed i'd only driven 30 some miles and its already 3/4 tank and at 70 miles its at 1/2 something is going on and i don't know where to start. Driving style was 65 on highway and light city driving.

 

Is your gas gauge giving you a false reading? Have you actually filled 'half' a tanks worth of fuel with only 70 miles?

 

i filled from gas light to full. 15 gallons and got 152 miles on it 10mpg.

 

something seems wrong. tune up lately?

 

yes something is wrong.
tune up yes, Plugs, wires, pcv, kn filter, fuel filter. cud it be the 4.56s?

 

What size tires? Did you recalibrate after the tire and gear swap?

 

265/70/16 and no

 

You need to recalibrate for the tire and gear change. The odometer and speedometer aren’t accurate.

What are the RPM's at highway speed? Did you notice the drop in MPG’s after the gear swap? If so, the low gears are causing the issue. 4.56's are very low for 31's.

 

so you got 152 miles out of im assuming 35 inch tires. Which are

35/29 = you travel 1.206 miles for every mile your odometer reads. So you actually went 183.4 miles/15 = 12.3 mpg.


Which still sucks obv. I'm just sayin, your math was a little off if I'm right.

(edit nvm way off, why the **** 4.56 for 31s!!??)

 

265/70-16 with 4.56 gears?? I think that explains your problem...

 

x2. Probably lots to do with the truck not being calibrated for the 4.56 gears

 

it was just one of those things you just do and don't think of it so i went 4.56.
how do i recalibrate it?
the rpms at 65 are 2700

 

You can do it with a programmer or tuner, or you can take it to a dealer. That won't get your MPG's back though. It will just correct the speedometer and odometer, which is also important.

What gears did you have before, and why did you change? The low gear ratio is the cause of the problem.

 

4.10 to 4.56, changed because i was planning a BL and larger tires but it wont be till the spring. its also LSD if that matters

 

How much and how long does it take to recalibrate at ford? Im guessing you rpms are way high especially at 65 with 4.56 and 31s. My 4.10s and 31s before would spin almost 3k at 70mph.

 

You'll just have to deal with the bad MPG's until you get larger tires. It runs around $100 to have a dealer reprogram for a tire and gear change. They won't be able to get it perfect, just closer. You need a tuner or programmer to get it perfect.

 

Yea ill just drive 45 instead of 50 and put the 100 toward a programmer. If one drives 200 miles with 33s how many actual miles are driven? If stock is 4.10s and 31s.

 

get a tuner, fix your problem

 

Yup thats the issue

 

You should have waited until you got the lift on and had your wheels and tires lined up, You wouldn't have needed 4.56's right away anyway if you were ganna run 33's. I do just fine with 33's and 4.10's

 

i have access to all ford scan tools at my school along with ford programmers and snap-off's higher end scanners and such. cud i do it or is it just better to by and xcal

 

xcal2 IMO

 

Yeah, gears and tires are part of the problem - a tuner will correct the tire size, speedo and gears, as well as tweak the N/V so you are shifting/downshifting properly (MAJORLY important). Also clean the MAF - I saw "K&N" in there, and an oiled MAF is a great way to kill MPG quick.

 

I am running 265/75/16 with the 4.10s and get terrible gas mileage as well. Stock tire size is 245/75/16.

Did a tune fix your mileage issue?