Problem with MBC/BOV

[CBT8503]

I just got threw installing my greddy type RS BOV. Before I installed it i was getting to 15 PSI, and immediately afterward the install I took the car out to make an easy 3rd gear run to find out how the new BOV was working. Boost went past the regular 15 PSI and on up to 23 PSI before I let off the gas. I stopped off at the next place possible and made sure the MBC was adjusted all the way out. I ran again and the same thing happened. Where could the problem lie? Do i need to soften up the BOV? And if so, how would i know i was at the right point of adjustment? There was also a clearance problem with the hood and the top of the BOV that i had to rig up a simple fix. Thanks in advance for the help.

 

[oldman]

Boost went past the regular 15 PSI and on up to 23 PSI before I let off the gas.

1. All out boost = boost shooting straight to 23psi.

2. Boost creep = hitting 15psi first then slowly creeps up as rpm increases.

Which do you have?

 

[CBT8503]

It shoots straight to 23 PSI. It doesn't slow down at 15.

 

[oldman]

Test run bypassing the MBC by connecting the pressure source directly to the actuator. If problem persists, the actuator is stuck open some how. If you get a solid 10-12psi, either the MBC is defective or it's hooked up incorrectly. Describe how it's hooked up and what brand/type?

 

[4GSixty3]

Try switching the 2 lines around on your boost controller.

 

[CBT8503]

I have a Joe P MBC and it's hooked up like it's supposed toas far as i know. I think that the old stock BOV just leaked hard. Could the BOV be set too hard?

 

[4GSixty3]

Your BOV has nothing to do with regulating boost. It's all in the way you hooked the mbc up or perhaps you bought a defective boost controller.

What kind of idiot are you?

 

[toojung2die]

He said he had the stock 2g bov before he installed the Greddy. You can't get more than 15 psi with the stock 2g bov because it leaks like a rusty bucket. When I switched from the stock 2g bov with a Joe P mbc to a 1g bov my boost shot up over 20 psi the first time too. He either has his bov set too high or hooked up wrong.

 

[4GSixty3]

He either has his bov set too high or hooked up wrong.

You mean his MBC is set too high? If this is the case, he has already said he has cranked it all the way out and the problem still persists.

 

[oldman]

He said he had the stock 2g bov before he installed the Greddy. You can't get more than 15 psi with the stock 2g bov because it leaks like a rusty bucket. When I switched from the stock 2g bov with a Joe P mbc to a 1g bov my boost shot up over 20 psi the first time too. He either has his bov set too high or hooked up wrong.

I have heard of boost creep being hidden by a leaking 2G bov which will uncover itself once bov is upgraded but not all out boost, this is why I asked CBT8503 which condition he was dealing with. If in fact we are looking at all out boost, perform the test run without mbc like I suggested will give you an indication of what the cause is. Also if the BOV is adjusted too tight, it will prevent the bov from opening which can cause compressor surge but shouldn't prevent the wastegate from opening.

 

[toojung2die]

I have heard of boost creep being hidden by a leaking 2G bov which will uncover itself once bov is upgraded but not all out boost, this is why I asked CBT8503 which condition he was dealing with.

I'm relating my personal experience. When I had the 2g bov, mbc and t25 I would get 15psi dropping off to 9psi at redline. When I put in the 1g bov I left the mbc adjustment alone. The first time I floored it my boost gauge instantly pegged (20 psi max). I backed out the mbc screw and was able to adjust max boost. CBT8503 has two adjustments to deal with now; the mbc and the adjustable bov. I agree that either one could be set too high.

 

[oldman]

When I put in the 1g bov I left the mbc adjustment alone. The first time I floored it my boost gauge instantly pegged (20 psi max).

The difference between your situation and his is that he has already adjusted the mbc all the way down and still getting all out boost.

 

[toojung2die]

You mean his MBC is set too high?

Doh! Yeah, what you said. Getting my TLA's mixed up.

 

[cool_g_83]

It could be possible that in essence when you first installed your mbc, you tightened it up to where it would hold 13 psi, in addition to what your wastegate is set at (thats how mbc's work wastegate = ~10 + MBC ~13 => 23 psi you see) though your BOV would leak at anything above ~14 psi.

So actually you could have been overworking your turbo for how ever long you had the MBC and 2g BOV combo (depending upon how much you WOT'ed).

Now that you put on your new BOV, it isn't leaking and is allowing you to see your true setting of 23 psi. Now, when you say you had backed it out all the way, it could be possible that the spring inside the MBC got snagged in the process of backing out the screw. This would explain your still seeing 23 psi and having the MBC backed out all the way.

Only way to know for sure is to bypass the MBC like oldman said above and if it reads ~10psi, you might want to disect your MBC to see whats up with it. Hope this made sense, and if it didn't, say so and i'll try to clear things up. Goodluck

 

[CBT8503]

Thanks for all the info guys. How might I bypass the MBC to see if the MBC is disfuncional? And dissect it as well? I'll give that a try and fill you in on the progress.

 

[wret]

Thanks for all the info guys. How might I bypass the MBC to see if the MBC is disfuncional? And dissect it as well? I'll give that a try and fill you in on the progress.

Just replace it with a piece of tubing.

 

[CBT8503]

I bypassed the MBC with a piece of tubing and it still wants to go past 20 PSI.

 

[oldman]

I bypassed the MBC with a piece of tubing and it still wants to go past 20 PSI.

That means the actuator isn't opening, as long as you did everything right. Before we jump into that conclusion, let's double check everything once again.

I have a Joe P MBC and it's hooked up like it's supposed toas far as i know.

The pressure source, coming off the turbo or T'ed off the bov/manifold line, should be attached to the nipple inline but opposit to the adjustment knob on the Joe P and the bottom nipple should be attached to the actuator. Make sure this is correct.

How might I bypass the MBC

Connect the pressure source directly to the actuator without going through the mbc. Make sure thereare no leaks in any of the vacuum lines used.

If the above conditions were met, you have a defective actuator that never opens. Good luck.

 

[CBT8503]

In the case that it is a defective actuator... what can be done about that?

 

[oldman]

In the case that it is a defective actuator... what can be done about that?

You can buy a new replacement, bone yard or call any vendor and ask them politely if they have any dead T25s. I'm a little concerned that you avoided twice in answering how the mbc is hooked up, it's important you verified that before you buy an actuator.

 

[CBT8503]

Sorry about that. The nipple that is opposite the adjusting knob leads to a T that lead to the bottom of the turbo. The wastegate line leads to the other nipple.

 

[oldman]

Sorry about that. The nipple that is opposite the adjusting knob leads to a T that lead to the bottom of the turbo. The wastegate line leads to the other nipple.

The wastegate nipple/line is at the bottom of the turbo, please clarify and be as detail as you can.

 

[4GSixty3]

It could be possible that in essence when you first installed your mbc, you tightened it up to where it would hold 13 psi, in addition to what your wastegate is set at (thats how mbc's work wastegate = ~10 + MBC ~13 => 23 psi you see).

Sorry about that. The nipple that is opposite the adjusting knob leads to a T that lead to the bottom of the turbo. The wastegate line leads to the other nipple.

How about you post a pic of how your MBC is installed

 

[CBT8503]

It's a little hard for me to explain, here is a pic i just snapped. The line that my finger is on leads to the nipple on the MBC that is NOT opposite the adjusting knob, or i should say the one that is opposite the flat side of the MBC. The other line (the one that is T'ed into the bottom of the turbo) leads to the nipple on the MBC that is opposite the adjusting knob.

 

[oldman]

I see, you still have the factory bcs hooked up so it's possible that the bcs is bleeding off pressure before the pressure source even reaches the mbc.

1. Remove the T along with the hose to the compressor housing nipple and the hose to the bcs.

2. Connect a hose between the compressor housing nipple directly to the mbc nipple opposite to knob.

3. Remove the hose from bcs to the little nipple near the mas on the intake pipe then cap off the little nipple.

Don't be afraid to ask about anything you don't understand, no one will laugh I promise.