WendysOrBust

So quick question regarding high milage ecoboost engines. I have 117k miles on my 2012 Ecoboost. I drive about 80% highway miles and it used to average about 18.5mpg. Now the highest I'll get is 17.3 with it basically being all highway miles, it also feels sluggish and doesn't seem to spool as fast. I've done all basic maintenance like air filters and spark plugs recently which helped a bit but now I'm thinking I should replace my cats.

Anyone have any experience doing this on their Ecoboost's? I did this on my old F150 with the 5.4, after about 150k miles it felt real underpowered and after I replaced them it felt allot better.

Edit: I'm sorry the picture uploaded upside down. Not sure why it does that when I take them with my 5s.

jgiddy

It could have something to do with carbon buildup on the intake valves due to it being a direct injection motor.

Commander316

do you have a catch can?

Joewee3.5

My brother had a high mileage bmw 335i. His mileage never went down but his performance did. Turd slow 14.4s in the 1/4 at 94. Those are well known for deposits. Seems like there would be a code for a cat issue. Good luck with getting this solved and I guess congrats on that mileage.

itguy08

Do you have a means to datalog it? May also be an O2 sensor going out could explain the MPG loss. That would also serve to show what's going on in the engine.

The butt dyno is notoriously inaccurate (they all are) so I'd focus on the MPG first and see where that leads you.

brettd4x4

Looks like your averaging about 36mph on that tank. That mpg seems good for that average

iknfixit

I'm at 135k miles and still 18.9 a good average. 87 octane lot of highway miles. 1k in towing camper. Late 11 model. Oil change every 10k mi none used between changes. I haven't noticed any decrease

iknfixit

Btw left side cat and inter cooler at 42k

Syclone Rob

could it be also the 'winter blend' in fuel and colder ambient temps which usually yield lower mpgs?!?!

iknfixit

Yep. I'll verify in a few weeks