hey i was hopin someone out there can help me with this problem ive been having for the last year, ive almost got the car running great except for after 4000-5000 rpm when i really push on it, it puls hard at first(1000-4500rpm) then from 4500-7000rpm it makes this sucking or breathing noise and loses power, id say almost like its losing boost or the second turbo isnt working....

i have noticed that one ove my chec valves dosent work right and lets air go back and forth ... would that do it or could it be somthing else ... i know my vaccum tank is good tho but it dose not retain air pressure...

what could it be?

 

Welcome.

Check out the 3rd gen FAQ thread stickied both in this forum and the 3rd gen forum:
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/faq-3rd-gen-other-useful-links-68640/

Scroll down to the T section for turbo where you'll find this link:
http://www.autosportracetech.com/RX-...erOverview.htm

Read through it to better understand the turbo system and how to troubleshoot it.

Your problem could likely be the check valve that you suspect. Very unlikely that its the turbo itself. If it was it would be smoking terribly out of the exhaust.