[logician]

The boost on my 930 goes up to 0.5 bar as measured by a separate VDO boost gauge -- the one that goes in the clock position. The boost pressure is tapped off of the brake booster vacuum line. This is with a completely stock engine and cat with 100K miles on it. The car was recently smogged on one of the dyno type machines here in Northern California and it passed with flying colors. When I replace the cat with a bypass pipe (actually a hollowed cat), the boost goes up to 0.7 bar. In both cases, I can hear the waste gate openning up.

My first thought is that the old cat is plugged up, and somehow affecting the boost limit. But the fact that the car passed smog makes me wonder if this is the case. Also, I can't really explain why a plugged up cat would cause the waste gate to open a a lower 0.5 bar pressure. I could see how a plugged cat could perhaps prevent the boost from going up all the way, but in that case, the waste gate would presumably not open. So I'm wondering if maybe there is another problem in the system.

Any help on this would be greatly appreciated!

-Juan