Going Around The PCV Valve
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Joined: Oct 2003
Posts: 69
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To the unmetered air concern. The PCV system is a ventilation system. Fresh, metered air goes from the snorkel - after the MAF measures it - and into the driver's side valve cover. The air flows through the block, picking up vapors or water, oil, and gas, and is sucked by manifold vacuum (after the throttle body) and into the intake manifold.
The same air that came out of the snorkel is now sucked back into the manifold through the PCV valve. It was metered before it left the snorkel so it is still metered when it comes back in.
As to mixture, other than the breather (filtered) air, it also picks up combustion byproducts as blowby, unburnt or misfired air and fuel as blowby, oil vapors, and water vapors. The oil vapors are slight. The burned combustion byproducts and water vapor is inert and doesn't affect mixture. The oil vapor (very little) and unburned blowby (should be little) will add some hydrocarbons (fuel) to the mixture but when in closed loop, it will be corrected for.
One caveat. Fuel gets into the crankcase if the fuel pressure regulator diaphram ruptures. That gas is carried from the crankcase into the intake manifold and that can create a very rich mixture. However, FPR diaphrams are not nearly ruptured as often as they used to be so this is rare now.
The same air that came out of the snorkel is now sucked back into the manifold through the PCV valve. It was metered before it left the snorkel so it is still metered when it comes back in.
As to mixture, other than the breather (filtered) air, it also picks up combustion byproducts as blowby, unburnt or misfired air and fuel as blowby, oil vapors, and water vapors. The oil vapors are slight. The burned combustion byproducts and water vapor is inert and doesn't affect mixture. The oil vapor (very little) and unburned blowby (should be little) will add some hydrocarbons (fuel) to the mixture but when in closed loop, it will be corrected for.
One caveat. Fuel gets into the crankcase if the fuel pressure regulator diaphram ruptures. That gas is carried from the crankcase into the intake manifold and that can create a very rich mixture. However, FPR diaphrams are not nearly ruptured as often as they used to be so this is rare now.
