Hey guys, i have a 2005 evo 8 that has around 57000 miles on it, i got it around 6/7 months ago and am starting too feel something is a little weird with my car. i smell my cars exhaust sometimes with the window down and it smells pretty damn rich and i get 8-11 mpg. 8 being me stepping on it constantly and 11 driving at fifth gear at 2100 ish rpms every day. i came onto these forms and saw other people getting 20-25 ish and wondered wtf. The dealer i got it from said everything was stock except for the 5 speed tranny swap. and in my theory, im just going too assume the car was probably pushing some power and the guy blew the 6sp tranny and needed too replace it and eventually returned it too stock too sell it but did not retune the air too fuel ratios that im stuck with. im still new too my car soo does this seem possible ? if so what can i doo too fix it THANK YOU FOR READING.

 

A failed O2 sensor is quite common and it will cause this.

 

Maybe check for boost leaks, does the car at least drive well? Do you have a wideband, can you tell what your A/F ratios are? A retune my be needed like you mentioned. Assuming your car is fairly stock, you should easily be getting 20MPG or more driving on the highway.

 

i'd check the o2 sensors. i find it hard to believe everything is stock but the trans, but it's bizarre that the dealership checked it over as everything being stock... o2 sensors would show up as a cel unless they disabled that cel... give it a check

 

Everything that was said above and is the car tuned? Evo's run stupid rich from the factory.

 

Consider the following scenario:

Everything wasn't stock. Car was tuned for power mods. Car was put back to stock (except for tune) for trade in to shady dealer. Car currently runs stupid rich. Mileage sucks.

 

Given that scenario the car would run lean not rich. Being it was tuned for mods and my guess larger injectors. So with that said stock injectors with tune for after market stuff would lean to lean. My guess is maf is taking over causing the rich condition. Just a guess but my advice is take it and have it tuned or find a stock tune and reflash it to stock.

 

I have basic bolt ons and a tune -- I get around 15 mpg...

 

Stock Evo 8, stock tune, interstate run on Monday, speed limit 75 which means we all were doing 80 - 24.3 mpg.

 

A friend of mine though he bought a "stock evo", started doing a TB change and clutch replacement and found aftermarket cams and upgraded clutch. Hopefully something simple like an O2 sens as someone had mentioned. Have you checked for any OBD codes? fouled Spark plugs? simple maint. goes a long way. (probably won't give you an extra 10 mpg. My Evo is bone stock and gets 22-25mpg city/hwy mix. I've heard with a proper conservative street tune they are capable of getting even better mpg.

 

Any check engine lights?