Is it a ball and spring or bleeder type (like the stock bcs) It sounds like you hooked it up backwards. Your wastegate could be stuck also. Did you hook the supply line up to the right side of the mbc. It is the side that has the ball. usually across from the adjuster bolt. And the other line goes directly to your wastegate actuator. If it is hooked up like that, take a pair pliers and see if you can move the wastegate arm at all. Also might be a bad wastegate actuator. To test it take it off and push the piston in and cap off the vaccum nipple. If it releases than you need a new actuator. I have a good used one it need it that i would sell you for 20 shipped. Check those other things first though.
mbc problem
I hooked up my mbc just like vfaq said and nothing it happening? i checked for leaks and screwed the mbc all the way in and nothing happend. I t'ed off the blow off valve line and attached that to the ball and spring side and the wastegate is connected to the other side. 
