Really Bad Mileage on 1.0 Ecoboost

[Reifhardt]

Hello
I have a 2015 sFe and I really like this car but I cannot understand why my mileage has plummeted. I bought it a year ago and like any gear head I immediately added an intake which made a big difference and did a muffler delete so I could enjoy that sweet 3 cyl rumble. Which also made a big difference. After a few months my mileage started to slowly get worse and worse. There was a time with both the intake and the muffler delete I was averaging 41 to 38 mpg with fairly aggressive driving. And when I would baby it I could get as high as 47. Now about 6 months later I'm down to 30 average and I have no cel's It runs smooth and still feels very responsive. I have changed the plugs, the oil, made sure tire pressures were good. So I started thinking maybe the mods were affecting it. So I put the stock airbox back on and it's actually a bit worse now. But after I did this I realized the performance felt exactly as it did before I put the stock box back on. Like the performance got gradually worse and I just hadn't noticed. So my next thought is does this fiesta automatically detune itself to stay stock? I figured it might need back pressure so my next step was to put a more restrictive muffler back on. I'm hesitant to take it to a dealer because they all suck and will charge me hundreds to tell me they can't find anything. I'm just at a loss. Any help would be greatly appreciated.

Also I have done quite a few searches before posting here and have come up with nothing.

Thanks again. Ben

 

[Spock]

I have the 4-cyl 1.6L engine and this time of year, my mileage has gone down by 4-5 MPG. I think it's the winter blend gas with 10% ethanol.

 

[rooSTer]

I have the 4-cyl 1.6L engine and this time of year, my mileage has gone down by 4-5 MPG. I think it's the winter blend gas with 10% ethanol.

What Spock said, winter blends do affect fuel economy.