No. You cannot disconnect the line to the BOV. when there is pressure in the line that goes to the BOV it keeps pressure on top of the valve keeping it closed. you MUST keep pressure in the line when testing.
When the vacuum line going to the BOV sees actual vacuum or LESS psi than is in the charge pipe, then the pressure forcing against the face of the valve from inside the charge pipe "wins" and makes the valve release which is when you hear the PPPSSSHHHHH sound.
When testing for leaks you must keep the vacuum line to the BOV hooked up.
Gotcha. I just did this to test out the BOV and seems to be working. I didn't hear any leaks. Im guessing it would have to be a really big, audible leak if I'm losing around 2-3 psi somewhere. I ordered the JPC Tial BOV. Once it comes, I'm gonna take out the fan shroud and spray all the tubes and vacuum lines with soap water and pressure test again just to be sure.
I'm gonna keep trying but had a thought. I was getting 9.5 psi with the 3.33 pulley and no WG. Boost did come in earlier and the data logs looked good according to Jon Lund II. If I can't find any leaks and I keep monitoring the belt, would it be bad idea to run it like this?