Manual boost controller bad ?
 

I was having my Miata's boost increased from 12 psi to 14 psi on a mustang dyno recently and the tuner told me that my Turbosmart mbc was bad because it would not hold vacuum on his Mityvac. So I bought another Turbosmart off of Ebay and the tuner said it would not hold vacuum either? Do mbcs even go bad?

Yep, they sure do. Ive had a couple fail on me. And, ive heard other say they have run into MBC problems

Just buy my AEM truboost and live happy.

WHICH so happens to be for sale on this site RIGHT NOW!!! O.O lol

I love my tru boost.

I don't see the virtue in a MBC if one has MS with boost output. The EBC's are less expensive and fully controllable. Am I missing something?

so an mbc should be able to hold vacuum?

If it's a bleed type then I don't see how it will hold vacuum. Ball and spring type should hold vacuum until the ball raises high enough to allow air to flow. Your tuner sounds like an idiot. FYI I'm pretty sure turbosmart makes a bleed type.

Oh and here is what a quick good search says in more technical terms so you can be educated.
Source: http://www.boostcontroller.com/display_page.php?i=22
With ball-and-spring types, a spring-loaded ball is used to block this delivered boost "signal", until the desired boost level is attained. It is at this point, that the delivered boost pressure is strong enough to push the spring-loaded ball toward the spring and out of it's seat, allowing the signal to pass, and reach the Wastegate Actuator. The boost pressure then presses against the Wastegate Actuator's diaphragm, causing its arm to move, so that the Wastegate is opened. The opened Wastegate then allows the exhaust gases to divert away from the spinning turbine, thus preventing the turbo from boosting higher than the desired level.

The MBC is adjusted by turning a knob (or other adjustor), which varies the load on the spring inside the MBC. By adjusting it so there is more load on the spring, you are 'raising the boost" because more boost pressure is required to move the ball off its seat before the signal can pass to the Wastegate Actuator. By contrast, lessening the load on the spring allows the boost signal to more easily unseat the ball and continue on its voyage to the Wastegate Actuator, so by backing the adjustor away from the spring, you are "lowering the boost". The Joe P MBC, and all Hallman Manual Boost Controllers, are ball-and-spring type MBCs.

With bleeder types, a valve simply "bleeds" off some of the boost pressure that it receives. It always allows some boost pressure to reach the Wastegate Actuator, but the boost pressure that the Wastegate Actuator receives is always less than the level of boost pressure in the charged portion of the intake system (or the boost level delivered to the bleeder-type valve) because this kind of MBC basically is a controllable boost leak. Since the Wastegate Actuator does not receive the "full boost signal", it only opens the Wastegate when the amount of boost that gets past the "leak" is sufficient to force it open. The bleeder-type MBC is adjusted by changing the size of the leak. Closing the leak down lowers boost level, because more of the boost signal then reaches the Wastegate Actuator, opening the Wastegate sooner. Opening the leak wider raises the boost level, as more boost is released to the atmosphere, as opposed to being delivered to the Wastegate Actuator as a boost signal; so the opening of the Wastegate is delayed.

Thanks for the info- I did some research on the turbosmart website and a diagram shows a ball and spring set up I think. I will do some more research to confirm this. Thanks for all the help.

The turbosmart "Boost Tee" is a ball and spring.

I guess I wii have to return the mbc I purchased from Wayland and get my money back. I'm learning as I go-too bad it's a trial and error process.