don't know the DV but its worth doing the normal test on it off the car. Push the piston up into the dv and put your finger over the vacuum nipple and check the piston doesn't fall down.
On the car, check the big hose and TIP clamped tightly onto the dv and that the vac hose is a tight fit and clamp/cable tie if necessary.
If the car is running standard boost you won't need an uprated spring as this will cause more problems.