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Discussion Starter · #1 ·
I've been dealing with a low/erratic boost issue, and my newest suspect is the CBV.

I decided to check my CBV with a vacuum pump yesterday, and when pumped up to 15 in-hg, it quickly bleeds down to probably 7-8, then slowly makes its way down to 0, all within 25-30 seconds. I know the diaphragm is good (it's a new iPd unit) but I have heard of the cover being warped and unable to seal. Is this normal behavior for the CBV or is it leaking?

Overall the symptoms I’ve experienced this whole time point to either the TCV or CBV, so I wouldn’t be surprised if that’s the problem. I've already tested the wiring for the TCV and tested probably 4 different TCVs. One gives me better performance than the rest, but I'm still making no more than 11-12 PSI of boost. This is a 2000 V70R with a Hilton stage 1 tune, I should be making more than that... and holding it.
 

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It should hold pressure tight. However, the vacuum fitting is not what makes it work. Its seal against the turbo housing is what holds pressure. But boost pressure to the fitting holds it closed so if that's leaking it's very possible that it won't hold against boost.

Basically how it works is that manifold boost holds it shut and as soon as the throttle plate closes, manifold vacuum pulls it open and it vents the pressure between the turbo and throttle back in to the inlet.
 

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Discussion Starter · #3 ·
That's how I figured it worked. I tried the same thing on my '98 and got the same results, and that car boosts perfectly fine. I assume my problem could be elsewhere.

I may just pull the turbo, it seems it's blowing a lot of oil even though there is literally zero shaft play. I'm at a loss... no clue why my boost is acting up.
 
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