breathers in efi valve covers=vac leak?

[PKRWUD]

Originally posted by jimmyjamed
your doing both. if your letting unmetered air in.... theres got to be a vacuum to suck it! if you take the oil cap off the valve cover, the rpm's will increase. put your hand over the hole and you'll feel the vacuum and the rpm's will go back down. lets say you disconnect the line from the pcv to the intake, wouldn't that be a vacuum leak? its still sucking ambient pressure, whether it goes thru the engine first or not. its less than ambient pressure where it taps off at the throttle body, which means less differential pressure, which equals less flow.

Yes, Grasshopper, but that of which you speak is crankcase vacuum, whereas the vacuum in question, is manifold vacuum. Manifold vacuum is the one that matters, because that is the air that reaches the combustion chamber. If a vacuum leak is developed regarding manifold vacuum, then unmetered air will enter the combustion chamber. Crankcase vacuum is caused primarily by a functioning PCV system, which in effect is really manifold vacuum. If you disconnect the PCV system, the crankcase vacuum should deminish.

To answer your question, if you were to disconnect the line from the PCV to the intake, it would only become a vacuum leak on the intake side. The hose going to the PCV valve would not be a vacuum leak. So, if you disconnected that hose, and plugged it at it's source (intake), then the other side of it (valve cover or rear of intake manifold, depending on application), would just be an unfiltered vent for the crankcase, not a vacuum leak.

Make sense?

Take care,
-Chris