This is hard to explain and this is my first time posting on here so bare with me. my 2008 evo x GSR is tuned to 25psi at full boost until about 5000rpm when it starts to taper down (on dyno sheet). the problem now is as soon as i hit full boost it spikes instantly from 25psi down to 15psi (and i mean instantly, on my boost gauge the needle literitly bounces off 25psi and back down to 15 rapidly) then rises to 20psi and back down to about 18psi until i let off (gauge needle jumps all over the place). this is all before 5000rpm and under WOT.. so it should be holding 25psi but its not (happens the same in every gear). what do you guys think this could be? mods done are intake, downpipe, catback, uicp, bov, and tuned on 91. could the stock boost controller be causing this? or a leak? any advice would be appreciated.

 

does it feel like power is bouncing around or is it just the gauge thats fluctuating? I have had more then a few boost gauges go bad on me, so if everything else feels normal it could just be the gauge. However if it does feel like power is all over the place, you should start by doing a boost leak test.

 

I had the exact same thing happen before during a log and I gave it a couple days and unplugged the battery for a couple of minutes and let everything reset and then it went back to holding boost just seems like the ecu trying to correct itself but definitely do a boost leak test!

 

Yes i forgot to mention that, but only during WOT or full boost will it do this, say if im going half it will hold say 12psi throughout the rev range as it should, this problem only happens when trying to hit full boost

 

Sounds like just a boost leak then once you get past 20psi!

 

boost leak would be consistent issue regardless of PSI. This sounds more like a wastegate issue.

 

interesting, would an upgraded wastegate actuator solve this if that is the case?

 

You should do a boost leak test...

 

That is not entirely accurate. I have had leaks that would not happen until 19psi or so. This was due to misaligned hose clamps. My symptoms were exactly as described by the OP.

 

Boost Leak