some issues i'm experiencing
 

So I've had my Evo for about a year and a half and I rarely drive it, usually only about 30 miles a week. The car has basic bolt on's Intake, exhaust, fuel pump, and a really safe conservative tune. The problem I am experiencing is I get very poor gas mileage. I tried changing out the plugs and it fixed the issue for a while but now it seems I'm getting really poor fuel mileage again. Changing out the plugs is an easy fix but with mine being a IX plugs cost almost $50 for a set of 4, so I don't wanna keep changing those out every few months. Does anyone have any suggestions as to what the underlying issue might be or how I can fix it?

-Thanks.

are you tuned? maybe due to lack of driving your fuel filter is clogged? could be a lot of things. stock 9 plugs? if not are they gapped correctly .025-.028?

o2 sensor

what about ur afr?????

i have the same prob my evo gets poor gas mileage but the plugs are fine plus whenever im stomping on it i feel the tranny grind a bit any suggestions?
:mitsu:

How hard do you drive it? If you get on it pretty good, gas mileage gets pretty terrible.

Fuel filter? Could be because you rarely drive the car as well, as that affects gas mileage over driving it daily. The evo in general is poor on gas mileage from my experience though, especially compared to my 350z which is a 3.5L V6...

you don't have to buy the uber expensive plugs, I buy the denso coppers and they work just fine. You'll have to replace them more often than the iridium plugs but they cost about 1/4.

What kind of mpg are we talking when you say bad?

So then whats the gain in changing your plugs 4x every 60k miles ( copper) rather than only 1x every 60k (iridium)?

I am on stock iridium plugs so they are pre-gapped. The car was tuned before I bought it and from what I was told by the previous owner it was a very safe rich tune. I don't drive the car hard at all due to this fact. I will occassional get into it a little bit and take it to about 6,000-6,500rpms but that is a very rare occasion (less than a handful of times in the year and a half I have owned the car). If it were the fuel filter then why would changing the spark plugs make me have good fuel mileage for a few months and then it go back down? I get about 60 more miles out of a tank when I change the plugs than when I'm running bad. I've been racking my brain and I just can't figure it out unless it's just the fact that the tune is rich.

you answered your own question!! obviously the filter is good, plugs keep fouling out. to much fuel...your tune is way to rich! have you added any parts to the car since you bought it?

you need to look up the thread on plugs, you don't need to run those expensive plugs

o rly? Please explain to us why not.

4g63 runs perfectly fine on NGK Copper core plugs. That is why.