Maestrozen39

Hello all.
I'm from italy and on my miata i run a small turbo configuration since 1 year and it always runned pretty good.
However, few days ago i've just changed intercooler, and also shifted to a full 2,5" intercooler piping (apart for the start piece from the compressor outlet, which is 2"), and since then i have some serious trouble gettin my BOV working.
I have a single piston good quality BOV valve that has always runned flawlessy, with no compressur surge at all and a distinct "psssssh" even at minum discharge of the throttle in the negative pressure area. The BOV vacuum source was not changed at all, nor the spring preload or the position of the valve in the pipe system, which is right before the throttle body. No other modifications were made at the car. Just the intercooler and the IC piping. When i started the car, in the first pull i noticed a strong turbo surge sound. Inspecting the BOV functioning, i noticed that the the valve remains open at idle. Revving the engine in neutral, the valve shuts and doesn't let the boost to release. Also i feel the car not very ready and powerful in the low rpms, due to the fact that the open BOV on idle/small throttle aperture don't let the pressure to build up in those situations.
I've tryed to adjust the preload of the spring, and the only thing i managed to obtain is to have the valve completely closed at idle, which improved the low rpms response, which returned the one i was used to, but still i wasn't able to get the valve open when it should, so still having compressor surge. Removing completely the preload didn't help.
Can you help me troubleshooting this? The only factors that are changed since when all worked properly are the intercooler and intercooler piping route.
However the car has a pretty good vacuum at idle and build up pressure nicely in boost, so i think that we can exclude leaks on the pipe routing.
Maybe i have to change the spring on the BOV? But why those minor modifications had made such a mess?

Ghostwhite

Sounds like the vacuum/boost source to the valve is not right, double check your signal line. If the signal line is good you may have a vacuum leak. The signal line should be applying boost to assist the spring in keeping the valve closed during boost and vacuum is going to overpower the spring and open the valve when the throttle closes with higher than idle RPM.

If you have inspected the valve to insure the piston and spring are moving freely then you likely have a vacuum leak.

Maestrozen39

The vacuum source is good, it's the first thing I checked, and to be totally sure i changed the silicon wire and used a dedicated nipple on the intake manifold.
For vacuum leak do you mean before or past the throttle body? Because past the throttle body it is nearly impossible. Also, i have 28.8 kpa of pressure at idle, which is good, and it's the same i had in the previous logs when everything was working fine.
However it's perfectly possible that i have a leak somewhere in the pressure line between the turbo and the throttle, but in that case i think the bow would work properly, and i would rather have low boost, am i right?

Maestrozen39

Update: I'm officially a ********.
Case closed!