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Installed MBC and now boost problems!!!

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pecka

15+ Year Contributor
61
0
Jul 20, 2004
Valley City, North_Dakota
Yesterday I installed an mbc on my car. It is the ball and spring type(i think thats what they are called). Well I go out to set boost and it wants to over boost all the time. I am trying to set it for 15psi, but it just wont cooperate. It spikes like crazy. My 1g bov also started making a funny noise when it blows off, it is almost like it flutters. What am I doing wrong? Could it be how I hooked up the mbc? I hooked one hose to the wastegate actuator and one to the line running off the bov. I blocked off the line coming off the compressor also. Did I do things right? Could it be the bov leaking?
 
pecka said:
Yesterday I installed an mbc on my car. It is the ball and spring type(i think thats what they are called). Well I go out to set boost and it wants to over boost all the time. I am trying to set it for 15psi, but it just wont cooperate. It spikes like crazy. My 1g bov also started making a funny noise when it blows off, it is almost like it flutters. What am I doing wrong? Could it be how I hooked up the mbc? I hooked one hose to the wastegate actuator and one to the line running off the bov. I blocked off the line coming off the compressor also. Did I do things right? Could it be the bov leaking?

Try hooking it straight to the compressor housing and see if that helps. Also, keep the vac lines as short as possible because too long of a line will cause boost spike.

It is also possible that the mbc you purchased is defective. What brand is it and how do you have the lines routed? Better yet, post a pic if possible.
 
it is a straight line specialties mbc, it looks like a joe p one though. I have the line coming off the mbc at the bottom (opposite side of knob) going to bov, and the other line going to the wastegate actuator. Could I have left both lines going to the compressor and wategate? Also the exhaust is stock.
 
Your spring may be too long also. I just replaced my MBC with the exact same style and my boost went from spiking to 18(down to 15) to no control over the boost. I cut 1 loop off the spring, and put it back together, and it works awesome now.
 
Give us specific numbers instead of "spiking like crazy". A typical T25 with upgraded bov in a leak free system is known to spike about 3psi to 18psi when set at 15psi, then drop off to about 13psi -14psi after 5k RPM. Have you tried changing the pressure source back to the compressor housing while keeping all hoses as short as possible like 92awddsm suggested.
 
i think i figured out the problem, my bov gasket was leaking and one of my intercooler piping connections was leaking, didnt have a chance to set it tonight though, i will try tomarrow, wish me luck
 
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