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2G BOV Opening During Boost Leak Test

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August578

Proven Member
100
23
Jun 15, 2021
Eastvale, California
Hi,
When boost leak testing should my bov be opening up?

I have a NGR type s

Everytime I try to pressurize my system it's basically releasing the air and the only way I can test it is when I cap it off, but even then it's hard to seal the hole off.

When driving it works like normal and I can hear it venting.



Any ideas?

Thanks!
 
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this can happen, you can try hold it down with a screw driver in the outlet port or jam it with something, i had this on my older type S when i had it on soft setting, was the only way to complete the BLT
 
Hi,
When boost leak testing should be my bov opening up?

It's not supposed to. During a pressure test the top chamber and bottom chamber should be at equal pressure and with the spring assisting the value should be closed. In operation when the throttle closes the manifold goes to vacuum, the top chamber will also and the bottom chamber will still see boost pressure which should overcome the spring and open the valve.

So try turning the spring pressure up. The valve shouldn't vent until you have positive manifold pressure and then close the throttle and many of those original and clone BOV's are adjusted too soft. Also make sure that the top chamber will hold vacuum so you know that the diaphram between the two isn't leaking.
 
It's not supposed to. During a pressure test the top chamber and bottom chamber should be at equal pressure and with the spring assisting the value should be closed. In operation when the throttle closes the manifold goes to vacuum, the top chamber will also and the bottom chamber will still see boost pressure which should overcome the spring and open the valve.

So try turning the spring pressure up. The valve shouldn't vent until you have positive manifold pressure and then close the throttle and many of those original and clone BOV's are adjusted too soft. Also make sure that the top chamber will hold vacuum so you know that the diaphram between the two isn't leaking.
Yeah - second this. Greddy BOV has a port for both sides of the valve diafram. The top port - pressure holds it closed, or vacuum helps it open. Bottom port, pressure tries to open, and the bottom never sees vacuum.

I've got the top port plumbed to the intake manifold, and the bottom port is plumbed to the intake piping just after the turbo.

During a boost leak test, the valve stays closed at any pressure, as the intake pipe and intake manifold are equal, so the spring in the BOV does not take much to keep the valve closed and sealed.

During driving, the same is generally true. On Boost, BOV holds most of the pressure top and bottom same (there is a differential between IM and turbo exit), so the spring is needed, and holds the BOV closed when the throttle is open. Depending on the flow of your inter-cooler, you may need to adjust the location of the lower pressure port in the intake piping, closer or farther away from the turbo to get the response you are looking for.

When the throttle closes - the vacuum in the intake manifold behind the throttle plate helps to open the BOV valve, so there is a nice fast, smooth release of pressure as the throttle plate snaps shut. On vacuum (idle) the spring is enough to hold the BOV closed.
 
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