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Originally Posted by dannmarr
I replaced the F connector with the hoses not long ago, I'll try to take some photos tomorrow for you.
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That would be awesome.
I actually have been reading up more on how the PCV valve works, and its a pretty amazing little gizmo, considering how simple it is. In particular, I finally understood why there is a connection to the intake and why this doesn't screw up the engine idle.
The PCV valve is
not just a simple one-way check valve like I had imagined. In fact it only lets air through if there is a
moderate difference in pressure : at zero difference or at high difference, it shuts off.
I checked this with a fresh PCV valve and a compressed air hose. As I began blowing from below (i.e., crankcase side) with my fingers forming a very loose seal, I could see the silver "pintle" inside the PCV valve raise up off the bottom seat and begin to let air through. As I increased the air flow, the pintle kept rising. At a fairly high flow, it hit its top seat, abrubtly sealing the passage shut again; this made the air seek another route and it squeaked audibly through my fingers.
So here's what the PCV valve does in practice :
At idle, the pressure difference is so high that the valve shuts off and does not let any air flow into the manifold. There's usually very little blowby at idle, but if there is any, it will flow from the crankcase to the air intake. While cruising, the pressure difference is more moderate, so the valve opens and some air flows from the crankcase (and the air intake) into the manifold. During a backfire, the pressure difference is in the wrong direction (and huge !) so the valve closes. At WOT, the manifold vacuum is nearly zero, so the valve tends to be "just" closed. If there is any blowby gas in the crankcase, this will open the valve. If there is a whole lot of blowby, this will close the valve again : this could be bad (pressurizing the crankcase), so that's why there is an additional line back to the air intake.
I feel a lot better now that I understand what all those hoses are about ! Hope somebody else finds this interesting !
p.s. After re-reading this, the only thing I'm still a little unsure of is the flow of
fresh air into the crankcase. My hunch is that at cruising RPMs there is a flow of air from the air intake, through the breathers in the heads, to the crankcase, which is then pulled through the PCV valve by the manifold vacuum. Sounds good enough for me.