Is the default position of the PCV valve open or closed? For example, my brake booster check valve is normally closed, and it takes a slight pressure to blow air thru one way. You can't blow air thru the other way. On the other hand, my current pcv valve lets a slight amount of air go thru the "wrong" way, but then if you blow harder, the valve shuts off.

 

The spring side will let air pass, so it is normally closed, until vacuum is applied to the other side and the vacuum pulls the valve open.

A slight leak on the vacuum side is normal, but when higher pressure is applied, it should close completely, which would be similar to a backfire in the intake, as to prevent it from going into the crankcase.

 

Thanks for the reply. I was worried that if the pcv valve lets the intake manifold pull a vacuum on the crankcase all the time, that it would pull out excessive oil vapors, causing oil loss and pinging (which is what I have).

 

The PCV valve DOES suck air out of the crankcase. It has to work together with the crankcase breather tube (goes to the intake upstream of the throttle). Do you have that vent disconnected or plugged?

 

no, I don't think anything is clogged or disconnected. I was just hoping, I guess, that the pcv valve was more like the brake booster check valve, i.e. normally closed, and requires a few psi to open. Wait... does it connect to before or after the throttle body? I need to check. I thought it was after.

 

The PCV valve connects to the plenum of the intake manifold (downstream of the throttle). The spring/plunger inside is set up like this...

Under weak vacuum (open throttle) it's relatively wide open.
With stronger vacuum (closed throttle) it moves & provides more resistance.
The general idea is to allow sorta constant flow rate even tho the manifold vacuum varies a LOT.

The other line (crankcase vent) is wide open to the intake, so the flow situation is dominated by the PCV valve resistance. That way the crankcase stays close to atmospheric pressure.

Also, if the manifold gets pressurized, the PCV valve closes completely. In case of backfiring...