Mitsubishi couldn't even diagnose my problem! lol
 

K we've been stuck on this for awhile, and still haven't figured it out! Took the car to two different Mitsubishi dealerships and they couldn't diagnose my problem! But they still charged me 120$! :(

Here's a rundown.

New parts installed:
-Fp wastegate
-10.5 hotside
-Ngk Bpr7es plugs (changed twice!)
-Megan manifold
-Megan o2 housing
-Hallman mbc

It started out just one day I couldn't boost over 10psi. We then discovered that the mbc was hooked up wrong and the Turbo xs mbc I had was crap. We tried changing the plugs, and switched mbc's and still nothing.

So, that led us to believe it was the wastegate. Changed the wastegate to an Fp wastegate and installed everything above (except hotside).
We accidently broke a stud off and the 9.8 hotside and I developed a major exhaust leak where the mani meets the hotside. When I got to 12psi it would just sputter really bad (which we assumed was from the exhaust leak)

So We then ordered a 10.5 hotside and put that on, reset the ecu and everything. No exhaust leaks, boost leaks, etc etc. . Still same problem!!!
It just starts to sputter really bad at around 10-12psi, won't build more build and the car hasitates horribly! (and by the way after we fixed the leak we changed the plugs, but it didn't help)

Anyone have any ideas, or does this maybe sound familiar to anyone???
I appreciate any help!!

Assuming the new plugs are gapped properly, did you ever swap plug wires/coil packs with another Evo? It's not uncommon for this to happen when one goes bad or gets burned through somehow.

Sputtering is almost always ignition related, so that's where I would have done my troubleshooting.

Maybe it's the ECM? I had a friend with a turbo Mustang that had a similar problem around 10psi, tried replacing everything with no luck, ended up getting a new ECM and fixed the problem. If it's bad, the dealer might not be getting an error code. Just a thought.;)

how bout the spring inside the mbc?

See I was thinking that might me the problem too. . .
But one thing thats wierd. . When it reaches 12psi, if you keep the gas pedal in the same position (almost wot, but not quite) I can hear air just fluttering out my bov like crazy! (And I do mean ALOT of air!) It almost led me to believe the maybe the flapper on the hotside isn't opening completly due to maybe a stuck wastegate?? So i'm thinking the air has no where else to vent except out the bov (and it comes out the bov WITHOUT letting off the gas)

Ecm? or ecu? are you talking the computer?

thought about that, but don't think it would make my car sputter as bad as it is.

probably not even close here, but did you try just putting the stock bov or another recirc one in?

No, that's normal. That's what happens when you try to accelerate in boost at part throttle. It totally kills the BOV if you do that - you need to be at WOT for it to work right.

Have you swapped plug wires and coil packs with another Evo yet? That should have been the 2nd test after putting in fresh plugs gapped to .026.

Going to try that today, but a few members from here told me that wouldn't be causing the sputtering. (At least thats what they said. . )

Do you have the stock bov? Stock intercooler piping. It sounds like a boost leak to me. Check your piping, or build a boost leak tester(search)

Basically your Mass Air flow sensor reads you are getting xx amount of boost, and then when you are leaking air it causes problems. Another thing is are you tuned? When I used to have an awd eclipse it did just about the same thing as your describing. It would boost and act fine until 12 or so lbs of boost. It was because it was reaching boost cut, and wasn't tuned correctly.

I'll try that. (I'm going to have to order some)
Sorry if this is a stupid question Warrtalon, but will a bad spark or something wrong with the ignition system cause boost problems? (i.e. low boost like I have now)
Sorry if I sound stupid asking that, but I really don't know the answer.

Unfortunatly, I sold my stock uicp and bov. Maybe I can find someone in Utah that will let me use theirs to test and see. . .

Only way it's a boost leak is if the leak springs open right at 10-12psi and opens up very wide. A normal boost leak would not cause any sputtering, and a big boost leak would sputter before building even 1 psi.

The causes for sputtering:
- Huge boost leak, but that keeps you from even building 1 psi and makes it hard to even speed up to 25psi
- Fouled, improper, or poorly-gapped plugs = causes sputtering right at peak boost
- MAF sensor plug not seated = causes sputtering and CELs
- Shorted/burned plug wires or coil packs = causes sputtering like the plugs

You're not having low boost problems - you are having ignition problems (sputtering). This isn't even about boost - it's about the sputtering.

There are plenty of other Evos in Utah. You don't know another Evo owner who you can swap with? It would take 10 minutes...