Hey everyone.
So my Sport Coupe gets pretty abysmal MPG averaging around 12mpg, by my approximation split 50/50 highway/city. I have a cold air intake, and high flow cats but if my memory serves me correctly, my mpg was about the same before the mods. What are some probable causes of this and things that I should check to correct this?

Thanks

 

heavy foot, spark plugs, bad fuel injectors, and bad O2 sensor

 

Are you manually calculating mileage or going off what the car says?

 

I’m experiencing the same thing. No not a heavy foot. I’m at 110,xxx miles. I need to talk her into a shop and just let them figure out what all is wrong with my G. Will let you know once I know!

 

Any roof racks or roof attachments?

 

Hey Hotsawce, it might be a good idea to start saving for a tuning software and get the car tuned. Many times while doing with Uprev/Ecutek we're able to identify much easier where the fault is coming from. Certain times HFCs can underperform and O2s will register this reading and affect your AFRs. O2 extensions are not always a fix. The tune could point these out, the tune as well once everything is checked/fixed can be adjusted to give you better driveability.

Being that you live in Miami(I live in Ft. Lauderdale) you drive more in the city than in the highway, i95/TKP are not always smooth sailing and lastly cruising speed will affect this as well. I remember reading a while back that the sweet spot on the highway tends to be 54-63MPH.
I cruise at those speeds for that same reason, I also dont bother to run more than 1/2 a tank since there is a gas station on every blink.

Try cruising at those speeds, 40psi all around, 1/2 tanks, if you're auto try throwing it in N while at the lights or idling. With these tactics I've been averaging 21.1 for the past 10 fills. Prior to the flash the best I saw was 19s
PS: my stock cats are failing as well. Unless you're a savage on the road there's no reason why it should be that low.

If you need help/parts/assistance hit me up. I live in Ft. Lauderdale and work in Davie.

 

Catalytic converter may be the issue