PCV System: Operation
With the engine operating, fresh air enters the PCV system through the air cleaner assembly. Fresh air flows through the crankcase breather and into the rocker arm cover compartment.
Entering fresh air combines with blow-by gases and unburned air/fuel mixture of the crankcase. Combined gases are drawn into the intake manifold, through the PCV valve, by manifold vacuum. Crankcase gases mix with air/fuel mixture and are burned in the combustion chamber. See Fig 1 .
The PCV valve is held closed by spring pressure when the engine is not running. This prevents hydrocarbon fumes from collecting in the intake manifold, resulting in hard starting.
When the engine is running, manifold vacuum pulls the PCV valve open, allowing crankcase vapors to enter the intake manifold. A baffle in the rocker arm cover prevents engine oil from being drawn into the intake manifold.
If the engine backfires through the intake manifold, the PCV valve closes and prevents any flow of gases through it. This is to prevent the ignition of fumes in the crankcase.