GSR running a 0.5bar only??? is that normal??
if its under the standard boost level, it could be the blow off going to die oredi, where it cannot withstand anything higher than 0.5bar... SQV can die also after a long usage....
or it could be ur wastegate actuator....premature opening at 0.5 bar...which would most likely cause ur engine to run rich fuel mixture, ... standard manufacturer setting will always give a considerably high fuel mixture even if ur running 0.2bar above the standard boost level... thats why when ur boost is lower than standard level, ur fuel mixture is waaayyyyy tooooo rich......thus backfire occurs and g-force all gone....
if evrything else is in good condition, what i'd do is get the fuel mixture dyno tune by using some piggyback(SAFC) or standalone... if u put a fuel reg on ur current problme, it will most like to give you an even richer fuel mixture....