I am the "somebody"
I had a big boost leak before on the UICP, the car was running OK, gas mileage was a little bit lower but it was at the end of winter. So I did not pay attention too much about my gas consumption.

I was able to see big clouds of black smoke after each big acceleration (between 3000rpm & 5000rpm). Friends were complaining about my car which skinked a lot (I have TBE with HFC)
I fixed the boost leak, the black smoke was definitely gone (I mean I was not abe to see it anymore thru the back windshield). I've improved the mileage per tank by 10-15 miles as well as spool up and lag.

since the MAF is before the turbo and the leak after, the engine believes that 100% of the air which went thru the MAF will go to the engine. In fact only 100% minus the air lost because of the leak will go into cylinders with still gas required for 100% amount of air ==> You'll run rich ==> black smoke.

This only occurs when boost is rising. After, turbo will provide more boost than required without leaks to hold boost target. The leak will wear the turbo faster as well.
Do not hesitate to correct me if I'm wrong

 

The hole was there in the intercooler from the old owner right before i bought it.But i don't understand how people get such bad gas mileage.If you just shift at 2500-2700 rpms and don't get on the turbo you can easily get 24 to 25 mpg

 

I understand also why your mileage is so good... I shift at 4000-5000rpm all the time even if I'm not on boost.
I'm at WOT at least 5 times every 5 minutes...

 

lol

 

one recommendation although it might not solve your problem is to throw in some gunmount injector cleaner ever 3k miles. Helped me a little with hp and MPG. But if your hitting that low I'd say theres another problem to be looked at.

 

i changed my spark plugs around 21k miles, not sure if it would make a difference in your case

 

Interesting, I need to do a boost leak test myself. Anyone in the NY area that could help me?

 

EGR vacuum line might have come off. Most times it would throw a code, but I've seen it come off without any codes too.

 

Your foot. You are gas happy .... j/k

It could be allot of things.

 

 

UPDATE:

So I took the car in to Mitsubishi service today and they called me to tell me that they can't find anything wrong with it, though they do recognize that getting 13-14mpg is not right. They told me that I should continue using the car until something goes wrong with it so they can fix it, but right now they can't identify the problem - there are no cel codes either.

What do you guys recommend I do? Should I take it somewhere else? I don't want to wait until something goes wrong with the car... HELP!

 

That's bad... I guess the dealer doesn't care about your gas expense.

I was complaining about a sticky gas pedal and a leak on my throttle body a while ago. The dealer told me: "there is nothing wrong with your car. It works fine!"
I've bought new gasket and fix everything by mysellf (without having done any mechanical stuffs by myself before). Now it works well Do a boost leak test by yourself. Ask support from your local Evo owners, there're plenty in Vegas

 

I average 135-150 miles per tank in Manhattan.

 

If your car is completely stock, I would take it back to the dealership and tell them that it's not fair to make you pay 14 mpg bills when the car clearly states otherwise. You should be hitting at least 18 when driving conservatively.

They should look at this now and not wait until there's another problem. That response is quite shocking to me...from my perspective, a dealership should have the attitude that the next problem to occur is far out.... if they expected problems every month, why would they sell the vehicle to begin with?

Keep us posted please

 

Check your o2 sensor. (the one in the o2 housing)

Find some one with an evo you can exhange with temporarely or buy one.

Check spark plugs, make sure they are gapped correctly and dont need replacement.

Maybe your cat is clogged? Have you ever ran leaded gas?