ThatGuyThere 54 Report post Posted March 19, 2018 In the process of diagnosing a supercharged GT86 - HKS kit. The impellor spins. The belt is tight. But seemingly no boost! Following a tip from Mark @ Abbey I looked at my Blow Off Valve. Visually seems fine. Although testing shows: At idle, it's open. Revving at stationary, it's remains open and more air comes through. So unless I'm misunderstanding - I have zero chance of boost building, as it just goes straight out through the valve. But unless the springs have somehow worn within the valve (they look fine) and with no sign of leaks from the thin pipe running to the intake manifold - I'm not certain where to look next. Should it be open at idle, and remain open while revving? Image shows an HKS BOV - not mine, but identical. Share this post Link to post Share on other sites
Mark@Abbey M/S 235 Report post Posted March 21, 2018 Adam, so at idle there is a vacuum to the Bypass valve so it will be held open. Free revving the car @ idle will not make any boost so the bypass valve will again be held open. The valve works so when when the car is running at high vacuum i.e small throttle openings it bypasses the charged air back into the the intake so the car will cruise without any boost. As I said we would just bypass the valve to check it is working properly , I am sure Jay on here had trouble with his bypass valve on the HKS install which he swapped out 1 ThatGuyThere reacted to this Share this post Link to post Share on other sites
GT86Jay 202 Report post Posted March 21, 2018 I have had issues with mine where the little rubber insert split. So even under vacuum wouldn't open. You could tell because when you revved the car you could hear the air flow on the blades making the typical pigeon fluttering noise that young lads in Mc Donalds Carpark seem to love. However it still made boost fine. HKS sorted me a new one out and was a simple fix. I can't get boost to build without driving it. What symptoms are you actually getting to suspect its got a problem? 1 Mark@Abbey M/S reacted to this Share this post Link to post Share on other sites
Rich196 103 Report post Posted March 21, 2018 @Mark@Abbey M/S @GT86Jay are are we saying that if you disconnect the vacuum line from the valve then you should be getting boost all the time? If so thats a very easy test? Share this post Link to post Share on other sites
Mark@Abbey M/S 235 Report post Posted March 22, 2018 @Rich196 no we are talking about blanking the pipe back into the intake. You will never get boost all the time as the SC will not spin hard enough at low RPM to produce boost Share this post Link to post Share on other sites
