Had a dump valve fitted for over two years now, a few days ago it started actin the arse! as soon as the turbo starts to spool up the dump valve is letting out the pressure while im still acelerating. As a result the turbo cant get goin properly. the car with a spanner thru it (light) has come on on the dash n the garage plugged into n sed low boost pressure and lamda sensor. ive stripped the dump valve down and cleaned it put it back but still doing it.