I use to get decent mileage.. like 16-20 but now im a 8-10.
Could it be my mods?
5/16 MD spacer, TDX2 exhaust, Art Pipes, Nismo Intake. I also changed my plugs like 1k miles before to NGK so im pretty sure thats not the problem.

What should I check out to potentially fix this problem?

 

O2 sensors will pull yer mileage down by about half.

 

I used to get 8-10 MPG and now I'm back up to 17-18.

Check for vacuum leaks
Sticking calipers (I had two of these) (Get an IR thermometer and check the temperature of each rotor)

Are you getting any codes around running lean or rich? Do you have an ODB scanner so you can check the fuel trim levels? I also put some BG44K in and think that stuff helped out a lot.

 

I complain about my gas mileage too. But I can't seem to keep my foot out gas pedal.

 

Time for a tune

 

This^^^hahaha

 

I'll also take your exhaust should be fine once you donate it to me

 

I bet a tune will help a lot. PM me and I'll help you save some money on it

 

He will, trust me ^^^

 

If you're getting 8-10mpg with normal driving there is something wrong with the car. Getting a car tuned that obviously has an issue is a complete waste of money and I seriously question a tuner that would tell you otherwise. Fix the car, then get a tune if you want one.

Checking fuel trims like coffey suggested seems like a good start. I've had old O2 sensors start reading way lean causing the car to dump fuel. If the ECU is making big fuel trim adjustments that's likely the culprit. Your mods should not have a significant effect on gas mileage, if anything you may gain a small amount.

 

There are a lot of things that we can check during the datalogging process that help to diagnose any potential problems like bad O2 sensors, exhaust/vacuum leaks, etc. Its still on you to actually fix the problem, but often times I can at least make an educated guess at what the issue is and point you in the right direction