I had a 2005 F-150 FX4 reg. cab stock and got around 15MPG on average. I traded it in and got a 2006 F-150 FX4 extended cab and I only got around 10MPG on average. I added a flowmaster cat back dual exhaust system and a Roush cold air intake and I now i get anout 12.5MPG on average. Both truck have the 5.4L in it. The 2006 has the engine that can take the flex fuel and use ethanol fuel. Does anyone have an idea why i am getting so much worse MPG with the new truck? I have tried running 91 octaine gas in it and it doesnt make much of a difference. What gives?

 

Weird, I would get a conservative dyno tune.

And maybe if possible remove the cat's.

 

pshh, you're lucky... I have the 2008 4.6L. I added the Flowmaster 40 series exhaust and an S&B CAI- I now get 12mpg ON A GOOD DAY =/

 

Wow, I really feel bad for you guys, I have the 4.6 in my truck and average 17.5

 

Are the tires the same size as your old truck? Is your filter clean?

I don't think the weight between Reg cab and Extended cab would kill it 3.5 mpg.

Are you driving the SAME?

Might sound dumb, but are you calculating it correctly? I know I've calculated mine wrong a few times and thought holy **** I got 21mpg. But I used the wrong number.

 

Pshhhh... Your lucky!!
I get 8 MPG. But I'm blown so yeah..

 

I have a 03' F150 5.4 and get 14mpg in the city.... that's running it hard.

 

I would also think of things like air filter, tire pressure, etc. One other thing, but I do not know how much of a difference it would make, is the oil weight. The Ford recommended weight maximizes mileage, so possibly the old owner was using a different weight. Unfortunately, I would think that this does not make a huge difference.

 

I average 20-21 no matter how I drive my TT Stealth... Haha. Sorry guys. Just felt is was necissary to throw that out there.

 

I have checked everything from tire pressure to the way i calculated the MPG everything is the same. I am driving the same who knows.