PRV Function?

[CortlandCH]

I’ve done a whole lot of searching for this answer, but there is a lot of mixed info online. Simply-put, what is the exact function of the PRV, and can it affect engine performance?

The PRV seems to go by many names. PCV, hockey puck, crankcase ventilation valve, and so-on.

My understanding is that it is a pressure regulator which helps restrict the flow of crankcase gasses in an engine under boost. Since the regulator is connected to the valve cover and TIP, it must be affected by intake pressure. When there is low pressure at the TIP, the valve in the regulator stays completely open to allow crankcase gasses to flow freely into the TIP. During boost, I figure the valve closes so that oil isn’t sucked into the TIP.

Is my understanding of this part correct? If so, I figure the main failure modes are:
Vacuum leak - if the valve diaphragm tears
Excessive oil in intake - if the valve fails to close
Excessive crankcase pressure - if valve fails closed

Any input on this, even just confirmation from anyone that knows anything about this part would be great! I’m waiting for a replacement part to come in this Wednesday, since mine appears to be failed open with a tear in the diaphragm.

[old guy]

Clicky click (https://www.audizine.com/forum/showthread.php/892936-Can-t-run-PVC-valve-04-1-8t?p=14119553&viewfull=1#post14119553)®

[CortlandCH]

Clicky click (https://www.audizine.com/forum/showthread.php/892936-Can-t-run-PVC-valve-04-1-8t?p=14119553&viewfull=1#post14119553)®
You never fail!

So my assumptions about the system were close, but incorrect. I guess I didn’t realize the PRV was an inlet to the block, and not an outlet to the TIP. I replaced my PCV last year, so hopefully it’s still in good condition now that I’m coming around to replace the PRV.

It’s odd to me that my PRV has failed, yet there are no misfires or odd changes in performance. I have noticed oil residue coming from the oil filler cap, so that would explain that issue. I wonder if I’ll notice any change in engine operation, aside from decreased oil consumption, once I replace the PRV?

[old guy]

You mentioned that your PRV had failed in an open position. The PRV is normally open. It gets pulled closed (with the small side port still allowing a slight flow) when under excess vacuum from the TIP. If it gets totally clogged up it can allow for excessive block pressure when under boost, since the block can no longer vent to the TIP. This can cause gasket leakage and excessive oil consumption.

[CortlandCH]

Well it'll certainly be good to change the part regardless. I didn't cheap-out either and went OEM.
I had sprayed it with soapy water, and plugged the side port with my finger while blowing into the bottom port (cleaned it first). I noticed bubbles coming from the small square hole on the bottom of the part, which I assume is where the diaphragm vents to atmosphere. That's how I determined that the diaphragm must be torn or worn.

[Halvis]

You mentioned that your PRV had failed in an open position. The PRV is normally open. It gets pulled closed (with the small side port still allowing a slight flow) when under excess vacuum from the TIP. If it gets totally clogged up it can allow for excessive block pressure when under boost, since the block can no longer vent to the TIP. This can cause gasket leakage and excessive oil consumption.

If the PRV gets clogged, does it result in any driveability issues?

[old guy]

I don't think a clogged PRV will cause any real drivability issues. But it would cause an excessive block pressure build up when under boost. This could result in excessive oil blow-by through valve guide seals and could also contribute to leaking and blown oil gaskets throughout the engine.

[Turbo510]

Also one on the 3.0 which has no turbo of course. I had some drivability problems when I first got the car, couldn't diagnosis it until one day the Crankcase Vent Valve 'honked' right after shutting the engine down. A new one made the car run normally.

[Halvis]

I sawed apart my old PRV to illustrate what Old guy has tried to explain in various threads.

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