i tried to search but all threads were without answers , maybe someone can give some advise or link to correct thread

my car goes on spool up to desired boost with mbc 20psi and than drops to actuator pressure 11psi , is this mbc problem , actuator or boost leak? i've retightened all clamps and checked vacuum lines , everything seems ok

 

What brand of MBC are you using? When you installed the MBC did you reuse the factory boost/vacuum lines, or did you use all new rubber hose and secure each end with hose clamps? How did you route the hoses to the MBC?

 

its actually not a brand one , when i bought car there wasnt any stock vacuum hoses , new hoses are without any pills , boost source is bov , there wasnt any problem for 2 years , but now it started loosing boost after spool up ... what is most common reason for that? boost drops only for 11psi and holds it till redline , who has same problem?

 

Try this test procedure: First, disconnect the MBC. Second, plug up the open hose ends. Third, connect a length of hose directly from the compressor housing's discharge (J-Tube) to the WGA. Finally, increase boost the old fashioned way by rotating the turnbuckle on the end of the threaded wastegate actuator rod. Raise the boost in this fashion until you reach your target boost level. If the boost level holds and doesn't taper back down to base boost level of 11#, then the problem is in that no-name MBC of yours.