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Discussion Starter #1
I noticed when I do a boost leak test, that I get some air out the BOV. This is with the throttle plate closed. Then when I open the throttle it stops. I was thinking that if the throttle plate is closed, that is similar to when I let off under boost and the BOV would open. It's very little air coming out, I don't really see the valve opening very much. Is this normal?
 

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Discussion Starter #3
the BOV should only ever be open when there's a vacuum on the nipple. it's leaking.
Damn. Mine is an older style with a vacuum source and boost source (on the charge pipe). Since I don't see the valve opening much, maybe the boost source is leaking internally? Turbonetics says the boost source provides faster response, but maybe I should unhook it and just try the vacuum source. Here is mine:

 

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The bov will open if there is enough pressure below the bov, and no pressure on the boost nipple. I made a T fitting to test my charge pipes, so I can put the same amount of pressure on "top" of the bov as in the charge pipe. When you open your throttle, you are letting the same pressure on the "top" as in the charge pipe, when the throttle is closed, you are just pushing the bov valve open with pressure.

If I were you, I would take the charge pipes off, cap one end, put pressure in the charge pipes, but use a T somewhere on your tester and connect it to the boost nipple on your bov.

The bov doesn't only open when there is a vaccum on the boost nipple, you could unhook the boost signal to the bov and it would open just from the pressure on the inside of the pipe.

Do you still have pressure in it when you open the throttle? If so, and it isn't leaking, you are good to go.
 

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Discussion Starter #5
The boost source is actually from my charge pipe right next to it, then the vacuum source it to my intake manifold. So the boost source sees the same pressure. Still pressurized when I open the throttle, and no air comes out. At idle it should be open slightly since that is vacuum, correct?
 

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The boost source is actually from my charge pipe right next to it, then the vacuum source it to my intake manifold. So the boost source sees the same pressure. Still pressurized when I open the throttle, and no air comes out. At idle it should be open slightly since that is vacuum, correct?
Not always true. My godspeed Rs 50mm. Was fully close at idle. But if I gas it some gas it would Crack open.

Reason being. That at idle you have around 21 in hg, but when u Rev and let off or shift you dip into 23 - 26 in hg.
 

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Discussion Starter #7
Not always true. My godspeed Rs 50mm. Was fully close at idle. But if I gas it some gas it would Crack open.

Reason being. That at idle you have around 21 in hg, but when u Rev and let off or shift you dip into 23 - 26 in hg.
Okay. What mine does it at idle or under light load there is a little air flowing out the bov outlet but the valve appears to be shut. If I push on the valve it still has air coming out. I thought maybe the vacuum/boost source were leaking internally but that would cause suction instead of air flowing out, right?
 

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Okay. What mine does it at idle or under light load there is a little air flowing out the bov outlet but the valve appears to be shut. If I push on the valve it still has air coming out. I thought maybe the vacuum/boost source were leaking internally but that would cause suction instead of air flowing out, right?
If the diaphragm is leaking it would cause a vaccum leak.
Of the valve is leaking or not seated all the way it will blow out air from the ic pipes.

You do have the nut on top which is normally to adjust the firmness and keep it close at idle.

But some valves are Crack at idle and fully shut right before boost is build.
Is your still Crack open when boost is build?
 

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Discussion Starter #10
If the diaphragm is leaking it would cause a vaccum leak.
Of the valve is leaking or not seated all the way it will blow out air from the ic pipes.

You do have the nut on top which is normally to adjust the firmness and keep it close at idle.

But some valves are Crack at idle and fully shut right before boost is build.
Is your still Crack open when boost is build?
I don't feel the air when building boost (using launch control, about 4psi), but then again it's so little that it's hard to tell. Once I let off it opens wide. I'm pretty sure the valve is shut all the way when leak-down testing, but I don't know where else the air would be coming from.
 

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If you want to find out if your bov is leaking, take the piping off. Plug one end, and tee off from a Schrader valve to get pressure on top of the bov. One hose going to into the piping, one going into the bov. Use soap and water. That will tell you 100% what is going on with your bov.
 
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