I have a 2014 evo x GSR and just recently started running about 15-16lbs of boost according to my cobb accessport instead of the 28lbs I normally run. I noticed the sound first, instead of the turbo spooling it's just an empty sucking noise. I've checked all the vacuum lines I can find and they all seem to be good. I haven't checked the wastegate yet but that's what i'm thinking it is.

My mods are the following:

-Cobb SF intake
-Tomei TI catback
-AMS test pipe
-Turbosmart BOV

irrelevant to this post but I also have tein flex z coilovers.

Any thoughts would be appreciated, I can't beat 5.0s on 15lbs of boost.

 

I don't really trust Cobb as well, but that's just me. Get the tune, get the compression test with a boost leak test.

 

A cylinder leakage test will give you a better idea of what is going on inside your engine if you are worried about engine failure.