Positive Crankcase Ventilation
WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 2003 Mazda Tribute, 2003 Mazda Protege5, 2003 Mazda Protege, 2003 Mazda MX-5 Miata, and 2003 Mazda MPV. However, it is still accessible from the selected car via links, so may be relevant.
The PCV system uses intake manifold vacuum to eliminate crankcase pressure. Manifold vacuum draws gases from the crankcase, through the PCV hose and valve, into combustion chamber.
By opening and closing in direct relation to engine vacuum, the PCV valve meters crankcase gas flow to the combustion chamber. During periods of high manifold vacuum, such as at idle and deceleration, the PCV valve is almost completely closed, limiting the flow of gases. During cruise speeds, the PCV valve permits the greatest flow of gases.
Under conditions in which excessively high amounts of crankcase pressure are produced (such as heavy load), the PCV system allows excess gases to flow back through the crankcase vent hose and into the intake manifold.