Wait, wait, wait. Your V9X has a BCS? I thought they were electronically controlled turbochargers. Ok. That changes the picture a little.
The BCS is probably the one component in my engine bay that I hate the most. Sure, I've replaced a couple of turbos, but that BCS is a painful little bugger. I've had 3, and now have a Tilix valve (like a Dawes valve). I also replaced all of the vacuum hosing (3mm rubber fuel-grade hose).
There is a way to test the BCS. It will have 3 hoses coming from it, one of these hoses will connect to something on the engine itself (not the turbocharger or the air intake). Find this hose that connects the BCS to the engine ("primary hose" ), get a new piece of hose and connect it to where the primary hose connected to the engine. Now connect the other end to the turbocharger actuator and take the car for a GENTLE drive.
I can't stress that "gentle" too much. If the turbocharger is working properly, connecting the vac pump directly to the actuator will pull the vanes open from the word go, which means max boost all the time. Your car will feel really powerful, but you don't want to be hitting the throttle hard and then stopping suddenly. Bring the revs up fine, but do it where you have loads of room to back off slowly.
If that's what you experience, then you should connect this new piece of hose back onto the BCS, reconnect the actuator and take the car for a drive again. If you now experience a lack of power, your BCS is POSSIBLY at fault. Replace the other vac hoses too, and drive the car again. If it's still weaker than normal, it's the BCS.
Nissan will sell replacements (about $240 or so in AUD) or you can go the alternative way. I have, and while my fuel economy isn't the same because the ECU isn't able to fine-control the turbocharger's boost, it's now 100% reliable.