I have a 2010 f150 screw 4x4 3.55 5.4L when i 1st got the truck i avgd 20-21 mpgs then my wife started driving it and was getting 17-18 mpgs now with 31,xxx miles we are strugling to get 15 i just figured it was her lead foot and winter blend gas combo but i drove it a few days and i cant get any better than her which is strange because i can always top what she gets garenteed

 

Wow I've got the same set up as you and never got 20mpg. I get 13-14 city and maybe 16-17 highway if I'm lucky. My truck has 10,500 miles on it

 

Someone has to have some ideas/insight (And i dont mean the "its a truck" stuff) i fully understand that but when im not towing and obey speed limits i do expect to at least get window mpg estimates espcially when the drive is 80% flat

 

Honestly the only time I get 20 is when I flip on cruise control and restart my mileage calculator on my dash. I average 15 mpg in stop and go driving. I don't think you have an issue man, I think you're fine.

 

I think the ECM learns driving habits and takes a while to relearn a different driver. I'm in Afghanistan and so only get home on leave every 5 months or so. My wife drives my truck on occasion and is a more subdued driver. Last leave I noticed the avg mileage was around 19 while I only average around 15. Even resetting the trip computer it took a full 2 weeks before the average dropped.

 

I agree with Waterfowler. I don't think the 5.4 isn't capable of 20 MPG unless you live somewhere where every trip you make is downhill.

 

I also have the setup as you.

As far as mileage goes, I average 17 around town and have gotten as high as 20.1 on the interstate cruising around 70 mph. And yes that's hand calculated. How-ever,, I'll also admit that I have a real feather-foot.

 

Try this: unplug the negative wire on your battery and let the truck sit for a minimum of 15 min. Reconnect and turn the truck on and let idle for a bit. Then drive it around like you normally will. As far as I know doing this will let the ECM learn your driving again. Between your wife and you, you both have very different driving styles. This may / may not help.

 

The 5.4 is very capable if you keep your foot out of it as i do, im pretty sure theres gotta be something wrong with it its goin to the dealer this week i was just looking for ideas of what it could possibly be

 

i have the same setup and average just over 18. two weeks ago and swapped vehicles with my wife. She got 7 MPG!! i couldn't get that bad if i tried.