bought a 2013 FX4 Ecoboost..68K miles..had heard people getting up to 23 highway mileage..took first trip, held at 70 and only got 15 MPG..that's awful, any ideas where to start? anyone else have this problem?

 

The efficiency of my truck falls off over 65mph. The boost starts to build to 2-4psi at 70+ and the mileage just dwindles...not quite as bad as yours though.
20-21mpg at 60-65
16-18mpg above 70

At 68k miles I would seek out a plug change though, as the EB is particularly hard on the plugs. A plug swap at the dealer should be about $350...less if you do it on your own.

 

I did slow some to see what the instant meter would do and it stayed about the same

 

Tell us a bit more about the truck.
Stock suspension? Wheels and tires? Any added weight, i.e. work boxes, bed caps, etc?

 

yes, stock suspension..275/70/18 grappler tires..nothing extra

 

My 2012 F150 3.5 EB with 373 gears will get 17 running between 70 to 75 MPH. Speed does kill the mileage fast in a truck. Grappler Tires are not doing you any favors when it comes to MPGs.
I would find it hard to believe someone is getting 23. My brother has the short bed, 2WD, extended cab 3.7L V6. He does get about 23+, however, he is a conservative driver.
What truck do you have? cab? gears? ...

 

275/70/18 Nitto Terra Grapplers are LT 10-ply tires. There's 1-2mpg for sure. Also are you recalibrated for the roughly 3% increase over the stock 275/65/18?

 

Reports of mileage are all over the board, it is hard to pin down a cure all. Some get great mileage, some get horrible mileage. I average 14 mpg if I am lucky, but I also do very little freeway driving. I did set the trip computer the other day and that mileage was more palatable at 16 mpg.

 

I've always gotten better mph with my Coyote 5.0 than most of my friends EcoBoost.

 

Compared to the '13 Eco at work that we've had since new, it doesn't get but 1 mpg better then my 6.2. In town or on the highway.

 

My 14 gets about 18.5 and the highway cruising around 72. It does drop to around 15 when I tow my boat which is about 8000# with the trailer.

I have noticed a little decrease in mileage on my last fill up, I am thinking that may have switched my area in Michigan to the winter mix for gas though.

 

The people getting 23 are driving on a 1% downhill grade the entire way in rural Kansas with the wind to their backs and the engine off with the trans. in neutral. Don't listen to them.

My truck at 70 MPH with the cruise set will get 16 all day every day. And the identical EcoBoost truck I test drove for a while before buying mine was getting about 0.5 MPG less.

There were myriad articles in the mainstream media when the EcoBoost was new dealing with how it wasn't living up to the fuel economy hype. It doesn't matter how many cylinders you give up, it still takes X amount of fuel to produce Y amount of power in these 5,800 lb. machines.

 

And here I thought FTE wasn't like the other Model specific forums...proved wrong once again.

Too many factors to say one is better or worse than the other. It does seem like the OP has an issue and some preventative maintenance would be helpful to rule out a few issues.

 

My brother in law's 2012 ecoboost was getting 15 mpg. He brought it to the dealer. They replaced 3 weak COP's and all the plugs. Now he gets 19 - 20 mpg. Idles so smooth it makes you think it died at the stop light.

 

My egoboost is getting a usual of 19-22 mpg on the freeway (3.73 gearing!) to and from work driving 65 mph on cruise control. One way to work is 32 miles and the road there and back is not very flat and one hill is at least a 4% grade. Doing 70 is about on par with what Tim is stating. Those grapplers are not doing you ANY favors for milage...people that put those tires on usually know they will have some loss in mpg due to the increased roll resistance.

One thing to check is to make sure the ECU has the most current flash...you can have them also reset the transmission learning. Also make sure the plugs are stock and maybe replace them as sometimes people re-gap them for a tuner they had and didn't bother to put it back when selling it. There are too many other variables to mpg that will not be the same across the board for everyone. Temperature does also play a factor...when it is cold the fuel mixture accounts for the change in air density and uses more fuel.

I would start with those things and go from there.