I know that theres far too many variables and what not to say what a truck 'Should' get. I have a 2005 5.4 Screw, 90k miles, 3.55 rear end. When I first got the truck at 46k it would get 16-17 on the highway without trying. Did the plugs at 60k, tossed in an Edge tuner since then. Now I am trying to get maximum MPG's and still 14.2-14.9 hand calculated on the highway. Driving smooth, all highway with cruise at 65-70 and about 500 lbs of passengers, empty bed. Tuner in stage 1 (trans only mode) seems to do slightly better, set at 2 (Towing) seems a bit lower.

No codes, no stumbling or noises. Fuel filter was just done.

Thoughts?

 

Thoughts on what...not tracking on what you're asking? Are you asking if your mileage looks normal or are you asking how to improve it? If the latter, I think you know the answer to that...or you can find it with a quick search.

Stock tires or larger?? If larger, the 3.55's are actually costing you fuel economy. Is your goal to save money or to improve fuel economy for the mental impact? At 14.9mpg, you're spending $0.20 per mile to drive. At 17mpg it's $0.18...that's barely $200 difference a year if you drive 10,000 miles a year. No modification you can do to solely improve fuel economy will ever give you a return on the investment. I personally don't think a loss of 1 - 1.5 mpg is indicative of a problem or concern. And like you said, the variables that could drive that small of a variance are unlimited...weather, fuel, you name it.

 

its not necessarily the drop but the fact that all the variables are the same as 3 years avo when I bought it and I was getting 17 on average. I am not necessarily concerned about a slight drop but with 5k miles of towing planned for summer vacations.... it adds up when the towing mileage ia already poor.

Front O2 sensors gummed up and not quite bad enough to throw a code?


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Try to find gas with less ethanol. What brand are you using?

 

The variables are not the same as three years ago...I guarantee you the gas may be different.