low boost 5KQ

[david.vickers at us.army.mil]

I am new to the list. I just purchased a 1987 5000CS Quattro. It has a Intended Acceleration Chip, 2Bennet Turbo and Intercooler, Koni Coilovers. I have had the car for about one weak. It drove great with 15psi of boost, and then suddenly it would not make over 5psi. The car still runs great up until 5psi; then, it cuts out. This is my first turbo. Any suggestions on where to start

David Vickers