Brantley said:
I don't know.. I'm still not quite following along here.
The turbo-specific PCV valve, the EV-127A, is a one way valve. As we know, this is supposed to only let air in under vacuum conditions. The valve that I made functions identical to the stock turbo PCV valve. It's a one way valve. Only difference is that mine doesn't distort under the pressure from hose clamps and it can't crack. Should be one less part to fail in the future. What's the difference between a PCV valve with a one-way check valve, or just a one-way check valve that actually works? Are you saying that the stock PCV valve is sort of a flow restrictor of sorts?
I still don't see how it matters about the metering part. The air is still metered by the VAM. The only place that the crankcase should be getting air from is the valve cover breather. In a stock configuration, that breather gets its airflow after the VAM. If it's getting air somewhere else, you have a bad gasket or some screwed rings.
(Hopefully this reply will seem somewhat intelligent. I need to put down the SQL book and go to bed!)
You are correct in one way.
The P.C.V. is basically a flow restrictor.
The air that enters the P.C.V. Valve is NOT metered by the VAM.
How can it be? the air being drawn through the P.C.V. system never passes through the V.A.M. so how can it be measured?
Why do you think it hurts performance so much if you have a huge vacuum leak? Simple. Because the Leak isn't being measured, because it's not being drawn through the VAM, therefore, the computer will not increase the amount of fuel to compensate for the additional air.
A broken or improper P.C.V. valve is basically like a vacuum leak.
The computer is programmed to know how much air will pass through that P.C.V valve at idle, therefore, knows how much fuel to mix with it, or in technical terms, knows how long to make the duty cycle of the injectors. When you build your own or buy the incorrect P.C.V. valve, the amount of air will be more or less than what the computer is programmed, and it can't tell any different because the air entering through the P.C.V system NEVER passes through the VAM, Mass Air, ect. So, the results you see are a high idle, a consistant miss, car won't idle.
Now, back to the Valve thing.
Like i stated before, a stock P.C.V. valve is just that, a valve. On a Naturally Aspirated valve, the pcv allows air to be drawn through it, pulling the plunger up in it as it passes through it. At Wide Open Throttle the manifod vacuum is zero, so the plunger falls shut. As the crankcase pressure builds up it can lift this valve and let the gasses escape very easy, with little or no effort.
Ok, now a turbo setup.
On a Turbo setup, the pcv is connected to a vacuum source just like above. Under idle conditions the pcv is held open by vacuum and crankcase vapors are drawn through it. When at wide open throttle, you guys see relatively 15 or so P.S.I of boost. What is boost? a measure of pressure in the intake manifold. Where is the pcv connected? to the intake manifold.
We are at wide open throttle with 15 psi or so of boost in the manifold. On the n/a setup the pcv plunger would be closed right now, so is the turbo setup. one difference. the 15 psi of pressure in the manifold is pushing down against the plunger inside the pcv vavle, holding it shut. pressure in the crankcase on the opposite side of the valve is starting to build, do to the pressure holding the plunger in the pcv valve being held shut.
I don't know how much clearer I can be.
Although the pressure in the crankcase should be able to escape no problem through the crankcase inlet, it should not build up even on the turbo motor, i really don't know what could cause it, this is just my theory.
BUT I do know the P.C.V. is metered, and if you like, i will photocopy the text out of my school textbook to get my point across.
when i was finish changing my plugs this weekend i start the car and it start then dies about 5 seconds later finally get i to run and it has a real ruff idiol idol surges up to 3300 then gose down to 3000 then it will die about5 minutes after doing all that when i looked at some things to make sure ihooked every thing back up and noteced the pcv was unpluged so i looked at it and it had brown stuff on it and looked pretty dirty so after all that could the pcv be the problem??
