right, turn the bleed valve right down, so its fully shut, ie so NO air is gettin past it. Then go and find a nice empty stretch of road, and get the car to 4000RPM in 4th gear, put your left foot on the brakes, gently press them and floor the accelerator. You should now be getting full load with the car being held back- boost should be at its peak, and it wants to be 15psi max. If its lower than this, open the bleed valve slightly and repeat the test. If it goes over 15psi once you have opened the valve, back off immediatly and turn the bleed valve back down