Broken mbc?

[dealz]

my mbc doesnt seem to be working right i tried boosting more so i closed it all the way and did 1.5 turns and it read 8 psi(which is what i do normally) then i closed it all the way and it went to 25psi with major fuel cut offs.i oppened it a little bit and it was back at 8psi WTF any suggestions.. thanks

 

[chanley talon]

Woops

 

[oldman]

The only reason it should leak is if you installed it backwards. The hole is blocked by the ball bearing.

Not true, think about it before you reply again. It will start leaking as soon as the pressure level reaches the mbc setting or when you go WOT if you will. This is the reason why disconnecting or turning the mbc all the way up is always step one when pressure testing. BTW there is no ball bearing in a mbc.

 

[chanley talon]

Its suppose to leak thats how it works. Why else do they put a relif hole in the mbc . Do you not realize it will leak no matter where you tap into it? Please dont get so angry! I never just say something with out thinking. I even said early that i would be willing to try it your way to see how it would work out. I dont know where you get thats theirs not a ball bearing in it made you should look how there built. http://www.geocities.com/chmwatson/FAQs/mbc.html

JUST LOOK AT THIS MBC LINK. I WILL NOT ARGUE WITH YOU KNOW MORE I GOT BETTER THINGS TO DO .

 

[oldman]

Its suppose to leak thats how it works. Why else do they put a relif hole in the mbc .

Has anyone argue that it's not suppose to leak? We are simply saying this is one of the reasons why one should not tap the BOV line due to this neccessary evil for the BOV's sake. BTW, the purpose of the pressure relief hole was not to create a leak under boost, that is just a unavoidable side effect, do you know what is the intended purpose of the relief hole?

 

[chanley talon]

Good ? To relive pressure i suppose.

 

[MrBoxx]

I think I know, so I'll give it a shot at explaining it.

The relief hole is there to "bleed" off boost pressure. This will delay the opening of the wastegate actuator by a certain amount, depending on how much of the hole is exposed by turning the adjustment screw. With the hole totally open, it takes longer for the pressure to reach the point where the wastegate will actually open, thereby raising boost. Conversely, with the boost trapped, it reaches the opening point sooner, and boost is lowered.

Am I right?

 

[oldman]

A wastegate pressure pressure relief valve does exactly what the name implies, relief the pressure trapped between your mbc and the wastegate actuator after boost level drops below the mbc's original setting preventing the wastegate from staying open in between shifts. Let's say the mbc is set to 20psi and you let off the throttle, the ball moves back to its original position as soon as you drop below 20psi trapping about 20psi in between the mbc and actuator, for a 12psi rated actuator, this means the wastegate will stay open resulting in anywhere between no boost to slow spool, depending on the setup, when you get back on the throttle. You were close though.

 

[luvmygst]

A wastegate pressure pressure relief valve does exactly what the name implies, relief the pressure trapped between your mbc and the wastegate actuator after boost level drops below the mbc's original setting preventing the wastegate from staying open in between shifts. Let's say the mbc is set to 20psi and you let off the throttle, the ball moves back to its original position as soon as you drop below 20psi trapping about 20psi in between the mbc and actuator, for a 12psi rated actuator, this means the wastegate will stay open resulting in anywhere between no boost to slow spool, depending on the setup, when you get back on the throttle. You were close though.

Dam** HE beat me to it.

 

[chanley talon]

Hey oldman is ther anyway you could take a pic of your setup and post it on here to see how you got it plumbed. Thannks i like to see it . If theres a way i can hook it up your way i will. I never like the idea off the bov thingy anyhow thats just what the directions told me . I have heard the mbc leak before. From that vaccumm line. Thanks

 

[oldman]

Hey oldman is ther anyway you could take a pic of your setup and post it on here to see how you got it plumbed. Thannks i like to see it . If theres a way i can hook it up your way i will. I never like the idea off the bov thingy anyhow thats just what the directions told me . I have heard the mbc leak before. From that vaccumm line. Thanks

No problem, I will try and take a picture of my setup for you when I get home tonight.

 

[mn95TSi]

i have probably almost, if not, the same thing in my car (with the little T to make it easy to twist haha)...

if this helps, mine is hooked up

wastegate actuater ------- T-Fitting (to J pipe) ---- weird MBC --- intake

 

[dealz]

ok i just bought a diffrent 1 from my friend and im gonna put it in thanx for all the help guys

 

[oldman]

No problem, I will try and take a picture of my setup for you when I get home tonight.

Better late than never.

 

[madman]

Ok so I've read this and changed the way my MBC is hooked up as mentioned in this thread. Now, instead of my vaccum reading -9.9 psi at idle, like it allways did, it fluctuates between -7.9 to -8.1 psi at idle.

I'm guessing this is a positve affect of hooking up the MBC directly from the turbo housing instead of tapping the BOV?

Why the change?

I also took off my IC pipes and put them back on, would this different vaccum mean I have a leak?

 

[oldman]

Ok so I've read this and changed the way my MBC is hooked up as mentioned in this thread. Now, instead of my vaccum reading -9.9 psi at idle, like it allways did, it fluctuates between -7.9 to -8.1 psi at idle.

I'm guessing this is a positve affect of hooking up the MBC directly from the turbo housing instead of tapping the BOV?

Why the change?

Sounds like you have created a vacuum leak during the process, go back and check everything you've touched. What did you do with the T on the BOV line?

 

[kawboy]

So the turbo housing has to be drilled and tapped for a custom fitting for the MBC, along with the WGS?

Wouldn't you have to dissasemble them to clean out the shavings?

More info?

 

[madman]

I put a new hose on from the BOV directly to the IM.

I edited the last post by saying that I had taken IC pipes off. I'll look into a boost leak.

I've had boost leak before but didn't affect the vaccum pressure at idle. Would this be in a different spot or indicate a leak some where else.

I also replaced my clutch so I had the whole transmission out but I didn't think that would be related, but maybe?

 

[oldman]

Pre TB leaks will not affect your vacuum reading, focus on areas between the TB and head, obviously I'm not saying to ignore the IC pipe leak. If the BOV line is the only thing you touched, focus on that line and fittings on both the IM and BOV. Did you touch the fuel rail trying to get to the fitting on the IM?

 

[kawboy]

So the turbo housing has to be drilled and tapped for a custom fitting for the MBC, along with the WGS?

Wouldn't you have to dissasemble them to clean out the shavings?

More info?

In additition, can these fittings be found at any hardware store?

Thanks

 

[madman]

I never messed with anything else like fuel rail.

I went out and checked all the IM and TB fittings. I noticed all my rubber caps for the TB lines on top are now dry and cracking. Maybe I'm getting a leak from them. I'll replace them tomarrow and check again.

 

[madman]

In additition, can these fittings be found at any hardware store?

Thanks

I think I got mine at Napa auto store.

My turbo housing was already tapped and had a plug in it. If you are going to have to tap yours, I would definetly be careful about metal shavings.

 

[oldman]

Just run a real boost leak test instead of guessing, soapy water will reveal little leaks real quick, might as well fix your IC pipe at the same time.