1979-1993 & 94 Conv [Subscribe to Daily Digest] |
The check valve is supposed to allow flow in the small line *from* the valve cover *to* the manifold, but prevent boost from going the other direction. The large line, from the turbocharger inlet pipe to the valve cover, is the crankcase 'breather' and allows filtered, metered air *into* the crankcase. The small line, with the check valve, is plumbed to the higher vacuum portion of the manifold and draws crankcase gases into the manifold to be burned through the engine.
What I've never understood is why they have both of those lines plumbed to the same place in the valve cover. I suspect a relatively large percentage of the breather air goes right back out through the vent line. On other cars the two lines are connected to different spots on the engine, so that the breather air makes a good trip through the oil vapor area, making it more effective.
I think you're right about the small line not being able to pressurize the crankcase significantly though (with the breather right there to relieve the pressure); I think the check valve really just keeps you from losing manifold boost pressure.
If blocking the vent line by turning the check valve around brings down your idle, I wonder if you don't have an air leak into your crank case area somewhere. When you have the check valve installed correctly (flow *to* the manifold), does opening the oil filler cause any change when the engine's running? It should. The crankcase is supposed to be 'closed', and all the PCV air (through both of the lines) goes through the AMM first. If you open the oil filler it creates a big air leak and the car should react, if not die.
Opening the oil filler had no effect on my car (also an '85), but in my case the air leak turned out to be the brake booster.
posted by 67.183.219...
, Thu, 13 Oct 2005 13:07:46, Wed, 12 Oct 2005 06:11:28
, Wed, 12 Oct 2005 16:50:25, Wed, 12 Oct 2005 09:50:16, Wed, 12 Oct 2005 10:00:52
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