of the main reasons for lost performance in a Roush M-90 is a bypass
valve that is not working properly. Over time the diaphragm inside the
valve can slowly start to leak causing a loss in performance.
Rebuild your Roush M-90 to full boost potential by replacing the bypass
valve. Or order one for a spare just in case. This
is a Roush service part and can be difficult to acquire but Brenspeed
has you covered .