Don't know the spring pressure, I don't here mine open up either. BOV is adjustable, adjust this BOV simply by twisting the top of the body itself, rotate it clockwise for a harder spring rate (for those of you at sea level) and counter-clockwise for a softer spring rate (for those in higher elevation)
Technical Articles | Adjusting Your Bov Or Bpv 1 | Turbosmart USA. If it was on and not set right before tuning it may now be a tuning issue.
There are some other things it might be but tuning is the most common. Worse case might be when the kit was installed and the fuel pressure regulator was drilled it may have gone to deep and ruptured the diaphragm.
My kit is starving for fuel even with my pressure regulator set at 60. Weird how this stuff works differently on each car..