I bought a 2006 Evo 9 back in September of 2015. Ran fine for few months than started like misfiring at low gears, than over about month and half got worse to where it does it in all 5 gears. It only does it when I WOT. Most psi it will reach is between 13-16 before starts cutting out. From outside the car sounds like it's backfiring. If I am in 4th or 5th gear and gradually bring it up to 13 psi and than floor the pedal works fine. No stutter, no backfire. I actually reached 28 psi. Car tuned at 3200: 21psi, 4600: 25psi, tapers to redline: 20. Max was 25, so shouldn't something, like Watergate?, prevent from going above 25? I don't know a lot about these engines and how they work, been learning.

Couple weeks ago I took it to a local shop. He looked at the wires to the spark plugs and said I'm 90 percent sure it's the wires. We made a deal and said go for it. As soon as I left the shop I did a pull, it worked perfect all the way through 3rd gear(as far as I made it) other than it backfired once but no stutter. Thought it might of worked. Decided to do one more pull and I think the top of 2nd it it just misfired hard. It actually didn't wanna stay running. It misfired all the way back to the shop(sounding like a suby). They also changed 3 spark plugs because they were cracked. I changed those not a week before that. They also said that timing was at 45 and at top of boost was -4. Don't understand all the timing numbers but he said that, that's not right. I hope haven't forgotten anything but just to the point where I don't know what it could be. Vaccum seems fine, plugs and wires changed. Any ideas or thought would be great been almost 3 months like this.
O yeah other than that problem car runs fine out of boost. I'll Post links to the videos of what's going on. Thank you!

 

Have you done a boost leak test?

 

evo 5th gear fluctuates boost when tuned, you should stay out of boost in 5th on stock ecu

 

No I haven't. I assumed there was no leak cause I idle between -19 and -21 inhg. Unless it's possible to still have a leak?

 

You should really do a boost leak test. And also, have you checked the spark plugs and gapping on them?

 

I haven't checked the plugs gapping no. Shouldn't they come pre gapped? Also what would you recommend gapping them too?
Plugs are brand new. Put in couple weeks ago

 

I personally gap mine to 0.024 but you should always check the gapping on them when installing new plugs as you never know if someone might have dropped them or something and messed up the gap

 

Ok thanks!

 

Amazing!
I took the plugs out and checked their gaps. They ranged from .032- .038. I put them all at .024 and runs perfect. Thank you!!!

 

No problem man!

 

Damn. I wish I could fix my car that easily