I have an 05 Expy with auto trans and 5.4 that I have owned sice mid 05 when it had 15K on it. I got around 17-18 MPG high way and 13-14 city back than and get about 13-14 highway and about 10-11 in town now with 60k on it. It is stock with the only after market part being a K&N drop in filter I put in on day 1. I have done all of the maintaince intervals in the book either my self or at dealer, I use only motorcraft parts and the recomended oil in the synthetic blend variety. I have cleaned the K&N and even went back to stock paper filter to see if that was it, no change. I am due for the 60K maintance stop with the fuel filter, trany fluid( dont you change the filter too? book only says fluid?) so that might help. I have the orginal stock tires that are on their way out but have even wear and enough tread to pass inspection. I run the pressure in them at 40 psi as this is the hightest I could go with out noticing uneven wear. I also will be putting new rotors and pads on as they are at the end of their life. I do mostly city driving and live in the northeast so I warm-up to defrost and run A/C. I track my mpg's about 80-90% of the time and have done with different variables (long highway trips, normal routine, mix of city and highway, heavy duke boys style, grandpa) and comes out pretty much the same with expected biases. Upstate New York has 10% ethenol fuel and I noticed the difference the same time I noticed the signs at the pump(1-2 years ago). I run 87 octane all the time.
Should I be concerned? Should I expect it to go back up after fuel filter switch(did at 30k as well before problem)? Is this what to expect with corn gas? Was thinking of some mods, but most I have researched my not be worth it.(computer tuner, cai, high flow muffler in place of stock) Thanks

 

The alcohol blended fuels do reduce mpg's about 10%. I would look at cleaning the throttle body, check the health of the COPS, check the muffler & converter for obstruction, and possibly replace the O2 sensors (although they should go 100k, but if they get lazy this can reduce mpgs)

 

thanks Beechkid,
Any product for throtle body cleaning? I use carb and choke cleaner in my 91 f-150 is that ok? Is the stock exhaust clamps with bolts to check for blockage (I can't remember noticing it) or different process needed other than take apart and look? Not familiar with acranim COPS in less you want me to check the health status of the local law enforcement.

 

I would avoid carb cleaner...since there is a coating ob the inside to prevent build-up...i use BG intake cleaner...most car dealers have this...if not, contact BG prodcuts for a dealer.

 

Original spark plugs still? If so they might be worth checking. They're supposed to go 100K miles, but not everything always goes as planned.

As far as cleaning the intake, use Seafoam. It's available at most any auto parts store and the directions are on the can.

 

+1 on the plugs. My 05 mileage jumped at least 15% with new plugs at 70k. Only broke 2 getting them out.

 

Hey a-teamer, any luck with this? I got the same thing going on with my 2006 @ 66k. I went from around 17-17.5 on freeway to 15 if I'm lucky.

 

Not familiar with acranim COPS in less you want me to check the health status of the local law enforcement.

COPS=Coil On Plugs

The loss of fuel economy is most likely due to the ethanol content in the gas. A pretty common problem for us all.

 

I would use the seafoam first. Then see if the mileage increases. Carbon build up will rob you of mileage and performance. Then change plugs if the mileage does not increase. I tend to go with the simple/direct/cheaper fix first. Here is a link to a good walk thru on seafoam.
http://expeditionforum.com/showthrea...hlight=seafoam

let us know how it goes.