My '91 GT recently has had a problem with the waste gate not opening. The power is great until the over boost sensor flap in the air breather box senses this increase in boost (shop manual says 9psi is max before alarm and engine cut out) and engine stalls. I've read other people have installed after market turbos with greater boost and none apparently have this problem. I've tried penetrating oil in the vacuum for the wastegate as the shop manual suggests and checked all vacuum lines for leaks, cracks, etc. and nothing seems to work. Does anyone know if I can install a stop on the back of the air flow sensor in the airbox to prevent the sensor from opening too far and sensing too much pressure? Any suggestions would be greatly appreciated.