I can't figure out why my fuel mileage is taking a dump.
I changed my fuel filter, added an Airaid drop-in filter and modded the airbox with a 4" bottom inlet and have been using the Brew for about 6 tanks now.

@ 50,000 on the odometer when I bought it the comp would give me around18.
Hand calc mpg before the changes was around 13.5[:'(]
Last fill up was 10.9!!!![:@]

Most of my driving is in town but I try to keep my foot out of it and keep the rpms no higher than 2000 to 2100 during acceleration.

What gives?

 

put the stock airbox back in and see if it comes back to what it was... i'll be it does. I'll also bet your turbo is spooling pretty quick which is causing the pcm to dump more fuel... causing your mileage to drop.

 

Maybe Winter Fuel! I'm not sure where you live so winter fuel may or may not be the problem. Also colder temps outside may cause problems, at least that is what I think has happened to me as my mpg has dropped 2.0 mpg in the past few weeks and it just happens that the temps dropped down in to the low 10 above zero to -15 below zero during the same time period.

 

I think cooler temps cause lower economy too. My mileage has been a little off too.

 

I'm in SE PA so I think we do get a winter fuel mix. At least I know we do for gassers.
It's probably a combo of the winter fuel and the airbox. At least I can change the airbox.

Thing is , I thought the increased airflow would have helped or is that only in older models?

 

oh yeah, forgot about the winter blend... also have you tried the brew?

 

I've put I think 6 tanks with the brew thru it so far.

 

put the stock box back on and see what your mileage is... I know some CAI & exhaust setups will loose mileage... when i had my magnaflow setup & afe installed, I got 1.0 mpg less than with the stock air box. if you put it back and mileage comes back, you have your answer.

another possiblity is leaky injectors...

 

Bert, my mileage has been takinga dump as well and I'm in PA also ( Philly ). I'm right at about 13.5 mpg average.

Yeah ... it sucks ...

 

I got 18.18mpg on my last tank and it was city and hwy. I used 16oz PSD and 16oz MMO , and I wasnt goin easy on it!! Its all stock.