Hi there,
I just started modding my car and I recently added
* Injen Dual Cold Air Intake (HR Engine)
* HKS Exhaust
* Eibach Sportlines

I've had all these on my car for 2 or 3 days and I noticed that my gas mileage dropped by more than 50%...
I just drove 75 miles and half of my tank is gone.

I know that I need an alignment as soon as possible but I am waiting for my springs to settle, could it be the reason why the gas mileage is so bad?
I know that alignment might affect gas mileage but I don't think that it can be that extreme.
I checked under the car to see if the gas tank was leaking but no, I'm burning it all.

I don't know if it can help you guys answering but I backfire... a lot?
I mean, there's no flames but you can hear the " ratatataa " or " pop " sound during the decceleration
Thanks for your answers & comments

 

No CEL?
Still have the cat's?

I find that adding intake and exhaust to any car makes me want to hear it all the time aka on the gas more often haha

 

NO CEL... Yet

And yes, I still have the stock cats...

LOL,
This is what a friend of mine just told me

" In theory, exhaust and intakes allow the cars to breathe easier and be more efficient. In practice..new mods -> louder -> thinks you're faster -> 50+ RicePower = **** MPG. You already have a symptom of severe lead foot... "

 

You might have a leak somewhere that could cause bad gas mileage too!

 

^ This

You probably have a leak somewhere in the exhaust or intake. Maybe even a loose electrical connection.

 

I'll have the car checked then to see if there is any leak...

Funny thing is I was getting 28.7 MPG today while averaging 65MPH...
But my gas gauge was going down like I was getting 1MPG

 

Your gasoline meter might mal-function too try to clean the sensor meter first!

 

headlamp fluid might be low

 

Alright well i had the same damn problem my mpg went down to about 10-12mpg pretty sad, anyway.... i have just a few more things done but still none the less i had no error codes and no clue what was wrong, if you havent tried d/c the battery over night i would try that first but what happened to mine was some how it got stuck in an open/close loop mode ( i forget which) and i did the battery crap it would drive right for like a day or 2 then crap mpg again and shitty accel so i broke down and got it tuned, not only did my mpg go up from 10-12 it went to 15-19 in town and 29 highway and some extra power. maybe looking into a tune might be somthing but do make sure its not a vaccume leak first.