My 2008 F-150 King Ranch w/ 5.4 ltr 3v has over 272,000 miles, is in perfect condition. I had to replace the trans at 250K, but the engine has been bullet-proof. No oil leaks, no oil burning. None! Changed the plugs at about 262K. Over the last three months, my MPG has dropped from about 17.5 to 13. Any suggestions as to what might be going on? I live in Ft Collins, Colorado. If anyone on this forum is from northern Colorado and can suggest a mechanic or shop that I can trust, I would be grateful. Thanks.

 

what method are you using to calculate MPG?

and over how many gallons and miles were the 17.5 and the 13 calculated, respectively?

what date did you change plugs and what plugs did you use?

any codes?

 

Do you have any Diagnostic Trouble Codes (DTC) stored in the trucks computer, autozone or other will check for free.
Often overlooked - I start by cleaning the Mass Air Flow (MAF). Use MAF cleaner.

 

no sure if you were getting 17.5 mpg to began with, that's hard to achieve unless it's all freeway driving at 55 mph.

 

Unless both of those computations were done over at least three different fill ups I wouldn't trust them. Just basing it one fill up can vary the gallons pumped because of differences in the pumps at different stations and how many times you click the lever after it stops the first time. And I agree with techrep that 17.5 mpg sounds questionable in my experience.

 

I have a 05 2WD F150 w/5.4 3V w/99K miles & the only time I can get 17 mpg is when I am on constant highway driving like when I drive from SW Va to Fla. I mostly do in town/highway driving & average 14 mpg.

 

Yeah 17 mpg is what I used to get too on interstate driving years ago when I tracked it.

 

Guess I shouldn't mention I'm getting 19mpg then, eh? 😁

Ft Collins sits around 5000' elevation, so that thinner air would be easier to move through. Probably why I'm gettng 19 too, my driveway is right at 6900'.

So, have you changed out the fuel filter? Air filter? Anything done to it that required the battery to be disconnected?

 

eh.

 

One post wonder.