MBC not responsive

[nightracer91]

Alright, I finally got my MBC installed and verified thru a few that the set-up was correct. This morning I began trying to tune it but no matter which way I turned the knob, it seemed to stay the same psi. Please advise.

 

[eklypse]

what kind of MBC do you have..? i know that on mine when i adjust it, i can hear the PSI get louder...you cant hear anything..?

 

[nightracer91]

Unfortunately, it is just an ebay one but I don't hear anything come to think about it

 

[fallenauthority]

Its probably installed backwards, flip the hoses and try it. Worth a shot.

 

[ChicksDigBoost]

Some of the ebay MBC's are junk and don't do a thing. I know a bunch of people that have had problems with them. What psi is it always at?
Verify that its hooked up one of these 2 ways:

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[oldman]

Never ever tap the BOV line for your mbc or anything else. Hose routes are different for ball/spring and bleeder type, at least tell us if it's a ball/spring type and how it is hooked up.

 

[ChicksDigBoost]

I probally should have said that tapping in the BOV line is not really they way to go, oh well.

 

[exile]

Regardless of the way you hook it up, it's still going to at least control your boost.

 

[oldman]

Regardless of the way you hook it up, it's still going to at least control your boost.

Hard to say, some poorly designed MBCs will take many turns to affect boost due to gaps in between the adjustment screw and the spring, assuming the casing isn't so big that the spring is lodged side ways to begin with.

 

[3134]

I have a turbo xs mbc and i installed it "backwards" and it did not do a thing. I then switched where I had the hoses connected and it worked beautifully. Where do you have your hoses connected? I would switch it around and go to a side street and try it out.

 

[nightracer91]

Like I said, the setup is correct. I talked to some guys in my local Club DSM and they said that it is probably that the spring inside the MBC is to weak. I don't feel any tension when turning the screw. I did some test to verify that the MBC is the problem and not a boost leak.

 

[dalatinromeo]

Well if it is installed correctly. Then do what you believe it is the spring. If that doesn't work, then see if you can install the mbc on a friend's car to verify it's the mbc not your car.

 

[geddytrams]

here's the thing. everyone says don't tap the BOV line for the MBC, but that's the way mine is tapped right now, and i can't figure out where to feed the MBC from. The MBC should be fed a vacumn feed off the intake manifold to ensure a consistant boost control. But the BOV should also be fed a vacumn source off the intake manifold because it needs vacumn to open.

Also, i've heard that the bottom nipple on a greddy type-s should be tapped to a direct boost source to help the BOV stay open during shifts (which is something i've run into, fluttering, or the opposite, having the screw out far enough that it doesn't flutter, but then i have a small whistling i can hear when i put my ear up to the intake filter.)

I have a Frankenstein Stage 4 turbo, and a greddy fmic, and i can't find a direct boost source between the turbo and the throttle body to tap for the lower nipple on the BOV.

So i think i need to set up the vacumn lines so that i'm not tapping the BOV line for the MBC. but i don't know how anyone does that.

can anyone tell me how they set it up to make it work?

 

[TheRealist]

Never ever tap the BOV line for your mbc or anything else. Hose routes are different for ball/spring and bleeder type, at least tell us if it's a ball/spring type and how it is hooked up.

What would be a good place to tap it at??

 

[AWDDSMCRAZY]

I bought a MBC off of ebay too and I had mine installed correctly and it didnt work. It would go crazy and shoot up to max psi. I took it apart and found that the output side of it was bored large enough for the ball to fall into. The ball was in the out side blocking the air causing it to act as if the hose wasnt even hooked up.

 

[geddytrams]

Where should i have the MBC tapped, and where should i tap the BOV to is what i'm asking.

 

[AWDDSMCRAZY]

I have my bov tapped to my turbo outlet elbow, while my boost control is tapped to my tb.

 

[geddytrams]

so you tapped your boost control to your throttle body? like, the emissions ports? i heard you couldn't tap it there becuase the source wasn't strong enough.

 

[AWDDSMCRAZY]

I believe that is where I tapped in, I removed my egr valve so that must be where I put it.

 

[oldman]

The MBC should be fed a vacumn feed off the intake manifold to ensure a consistant boost control.

Nothing but a myth, the boost gauge is tapped at the manifold so whether you're tapping the manifold for mbc makes little to no difference in what you see on the boost gauge. Even if you're insisting tapping the manifold, stay off the BOV line because the MBC wastegate pressure relief hole will bleed pressure off the BOV line causing the BOV to open under boost and not fully and quickly enough right after letting off the throttle. I'm not saying your problem right now is due to tapping the BOV line, I think your problem is the MBC itself, but the BOV line should never be used for anything but the BOV.

What would be a good place to tap it at??

Where should i have the MBC tapped, and where should i tap the BOV to is what i'm asking.

Without getting into why, the best place to tap your MBC is the compressor housing/turbo outlet/J-pipe, picture number two in post number 5.

I have my bov tapped to my turbo outlet elbow, while my boost control is tapped to my tb.

Please explain how will your BOV ever open if it's tapped at the turbo outlet pipe, you need to swap your BOV line back to its original fitting on the IM before you kill your turbo, In fact I'm shock that you have not killed your turbo yet.

 

[AWDDSMCRAZY]

Lemme go double check I thought thats where I had it but I'll check quick

 

[AWDDSMCRAZY]

I guess I was wrong I had it backwards. My bov is tapped in at the tb while my boost control is at the turbo outlet elbow. Is this ok? Im installing a new turbo tomorrow so I really dont want it to damage it. It's tapped to the bottom vacuum connector on the side of my 90's tb. I've been trying to eliminate and clean out the engine bay. Only using vacuum lines needed etc. I saw a diagram of minimum needed and thought I followed it.

 

[oldman]

I guess I was wrong I had it backwards. My bov is tapped in at the tb while my boost control is at the turbo outlet elbow. Is this ok? Im installing a new turbo tomorrow so I really dont want it to damage it. It's tapped to the bottom vacuum connector on the side of my 90's tb. I've been trying to eliminate and clean out the engine bay. Only using vacuum lines needed etc. I saw a diagram of minimum needed and thought I followed it.

MBC on the turbo outlet is perfect. As for the TB fittings, the only one that is acceptable to be used for either boost gauge or BOV is the "p" port but I don't know which is the "p" port on the 90' model. I can however tell you that the bottom side fitting isn't it because it runs to the front side of the throttle plate, you need a source after the throttle plate for your BOV. What's wrong with your original BOV fitting on the IM? Do you have a SMIM without vacuum fittings?

 

[AWDDSMCRAZY]

Honestly I got angry after buying the car. The only thing said to be wrong with it was the water pump. I sent the guy money. Went and picked it up and trailered it home. When I got home found wires not hooked up all over the engine bay. Vacuum lines cut and or missing. The rear diff was stripped out, looks like they removed all the pieces of the ring gear. Basically I just ripped out every wire and vacuum line I could find and started looking at the manual for wiring and the simplified vacuum routing which I found on here. The diagram showed IM, but I figured I needed to block off the tb nipples somehow.

We are installing my new fmic and turbo tomorrow so I will redo all the vacuum lines. Thx for the tip. I'll have to just plug them or loop a vacuum line from one to the other. Now I just need to figure out whats up with the timing. Stupid thing knocks under boost without race gas.

 

[TheRealist]

MBC on the turbo outlet is perfect. As for the TB fittings, the only one that is acceptable to be used for either boost gauge or BOV is the "p" port but I don't know which is the "p" port on the 90' model. I can however tell you that the bottom side fitting isn't it because it runs to the front side of the throttle plate, you need a source after the throttle plate for your BOV. What's wrong with your original BOV fitting on the IM? Do you have a SMIM without vacuum fittings?

i do not have a jpipe so whare would i tap mine? i have the stock t25