My 2014 3.5L EcoBoost super crew lariat has been a real battle the last year+ engine wise. It's used as my primary work/personal truck. It has 145k miles on it and the gas milage has been dropping for a while. At 70k miles I had to replace the boots wires and plugs because of a carbon buildup issue (which I'm reading is common). Fast forward to this year at about 130k I had to replace all those again for the same issue. Then at 140k miles the throttle body gave out..... carbon buildup issues again according to factory service. Now at the 1st change of boots wires and plugs I was getting about 17.7 mpg combo city/highway at 70k miles. I'm now down to 13.8 mpg and getting highly frustrated with the performance, all which has been said to be just fine by 2 different factory service centers at Ford.

I also have a 2007 shop truck with 280k on a Triton v8 and a 2016 v8 lariat that are both getting significantly better gas mileage. The 2016 is aluminum body so that's understandable but how is the Triton getting better mileage than this EcoBoost? Is the engine flawed or is this just what happens to turbo engines over time?

Basically what I'm asking is this time to just trade it in and go back to V8 power?

 

Reading your post I think you would be happier with a V8, as there really isn't that much difference in MPG between the V8 and eco-boost anyway.

 

There are mechanics and then there are mechanics if you know what I mean. Losing 4 mpg and being told everything is fine doesn't sound right. But, your problem could have many different causes. Too many to just start guessing. If you do a lot of hi-way driving I'd do a quick check of boost pressure before starting to tear in to anything. A bad intercooler keeping pressure down can do this to mileage and it's a quick and easy check.

 

When's the last time you replaced the air filter?
.

 

^^

 

Air filters often do get overlooked, I don't even change mine as often as I should.

 

Might be time to consider doing a cylinder leak down test. With all the carbon build up issues, I think it may be time to find the root cause of the carbon build up (we could all sit around and guess/speculate at what it MAY be...….but a reputable shop/mechanic is what you need). Or you could just trade it and start the whole process over again.