Hey guys, I'm new to this, never posted a thread so forgive me for any post errors.
I have a 2003 Evo 8, 130k, engine is stock except for a greddy cat-back. And I have a boost gauge, but no wideband.

only problem Ive had up to this point is cylinder 3 spark plug has an issue fouling. maybe running rich, but never solved before the main issue at hand with my turbo...

A few weeks ago I was getting on it on the HWY, around 100mph, got off the exit, and after accelerating I noticed a significant loss of power. No boost at all! Right at zero when accelerating, but normal vacuum. Car idles fine...just of course accelerates like a POS Checked for loose IC piping, nothing.
Since then ive done a boost leak test and didn't find anything. Also checked the boost actuator, it was fine. Took off my turbo and took it to a local turbo shop to see if they could tell me anything. They found nothing, everything looked good and in good working order. I have a theory about it being an issue with my cat, but not sure. I'm new to this, bought my Evo in March, so any help you guys could offer would be GREATLY appreciated!!

 

I don't know about 0 boost, but if you had significant enough knock it could have put you on the low octane maps which would certainly reduce the power by a large margin. Something about your description of the situation doesn't really add up, with a fully functional turbo and no boost leaks it should be virtually impossible to make 0 boost. The stock WGA has a 14psi spring in it so even if it was hooked directly to a boost source you would expect to make at least around 12 PSI. Maybe verify your boost gauge is working properly as i have had many go bad on me. Also could you describe the method you are using to perform the boost leak test?

 

I don't believe my boost gauge is malfunctioning because as soon as I had a loss of power is when my gauge registered no boost.

and for the boost test, I took the coupling off the upper IC piping, capped off both ends, one with a mail adaptor for a compressor. used about 15psi, and gauge showed it held boost.

 

You need to cap off the turbo inlet to pressure test the whole system and you need to use a couple more psi then the max psi you run.

 

Crap that makes sense! Lol I'll do that soon. Just got the turbo back so need to reinstall everything.

 

I see you said your car has 130k miles, I would check your cat. I know someone who had a clogged cat and his car had about 100k miles, car was making about 2 # of boost and sure enough replaced the cat and it was good again

 

yea, that's what I recently started thinking was possible! I don't think it's a boost leak because it went from 18psi to 0psi. I wouldn't mind a catless downpipe anyways haha

 

Just an update guys, turns out....it was in fact my cat plugged up! Bought a catless downpipe from a member, and solved the problem! Back to normal, full boost! Darcy's fartin like a champ!