Boosting issue (Hitting Overboost shutdown)
 

Hey guys. Ran into a boosting problem and I can't seem to figure it out. Before I get into it here some background info on the car. 1993 FD, streetport, power fc, single turbo BW 9180 EFR, glease man twin scroll manifold with twin wastegate 38mm tial wastegate (15 pound springs) controlled by turbosmart e-boost street controller, Turned at 18psi.

Problem: Car will begin to build boost and just before target boost pressure (18psi) it will trigger the "overboost shutdown" feature on the controller and go to spring pressure (15-16 pounds). The overboost shutdown is set to 19psi. Tried turning down the sp value (duty cycle) and the sensitivity and the problem still happen. What's also weird is that the problem sometime happens and sometimes it doesn't.

At first I though something was loose or a vaccum leaking, but I checked everything and it was fine. The next thing to check was the wastegates. I pressure check them and both were fine. Now im thinking maybe its the boost controller unit or the boost solenoid.

Any help on is greatly appreciated

Thanks guys,

That seems to be a really irregular issue. The only thing that strikes me weird is that the spring pressures are really high and generally people run a lower spring pressure and control boost with their ecu or an electronic boost controller. Do you notice a difference whether the car is running hotter or not? It's a possibility that boost is building too quickly for the controller to catch and it automatically resorts to the overboost setting that you're describing. Try running a lower spring pressure to see if that changes anything. Twin 38s are also fairly low on the cross sectional area for how much exhaust energy your engine is putting out with such a big turbo. Big power means big exhaust energy which requires big wastegate flow.