Hello,

My 2008 Fit Sport gets poor gas mileage 24-28 on the highway. It has an aftermarket Megan racing header and a cold air intake. The check engine light is on due to an 02 sensor code. I tried to change the 02 sensor with no change in mileage. Before I go and start buying new parts here are some questions I have:

Do I need a specific type of 02 sensor for the Megan Header (I just used the original model)?

Would it be worth reinstalling the original air intake and header?

Thanks. I just want this car to be a good, economical highway cruiser and don't need the added performance of the aftermarket parts.

 

If you want to know for sure, return the car to stock, clear the CEL, and see if the fuel economy gets better and the CEL stays off. If so, you can then add one aftermarket part back at a time to figure out where the problem is.

 

Make sure your Airflow sensor is attached to your CAI or Ram, and either your 02 sensor is bad or the cars computer is having trouble reading the change with the new part without a tune up.
oh and check your coil packs also

 

There is no airflow sensor on GD3, it uses MAP

 

I came to this thread looking for the same thing, wondering if MAF needed to be cleaned, seeing recommendations elsewhere that one should consider cleaning MAF sensor with something like CRC MAF cleaner, sort of as part of regular routine at the same time as changing air filter. Just installed new filter on my '08 base, and found that I couldn't identify MAF. Turns out, I may have been looking for something that doesn't exist.

 

While someone may agree or disagree, I would name 3 reasons:
1) Short driving around the town (let say 3 miles round trip)
2) driving in city during rush hour (full throttle starts followed by hard stops) to get around school bus , garbage truck or in attempt to beat up several traffic lights)
3) deteriorating A/F mixture sensor (which interprets normal mixture as lean); when it dies it sets P0171 -lean- code leading to long troubleshooting and unneeded replacement of the fuel pump.
Item number 2 combined with piston slap, fools the knock sensor leading to retarded timing; in attempt to maintain requested acceleration pace the a/t downshifts to the lower gear increasing engine RPM and fuel consumption; with MT the engine starts to labor at much higher rpm forcing driver to downshift.

 

You more than likely need an 02 fooler/spacer since youre running the header. I had that issue on mine. The sensor is reading that its running too lean so its causing the car to throw more fuel at it than needed causing your poor economy