Positive Crankcase Ventilation: Description and Operation

PCV Operation:

The positive crankcase ventilation system (PCV) operates to consume crankcase vapors in the combustion process instead of venting to atmosphere. Fresh air from the throttle body is supplied to the crankcase, mixed with blowby gases and passed through a PCV valve into the intake manifold. The PCV valve meters flow at a rate dependent on manifold vacuum.
To maintain idle quality, the PCV valve restricts flow when manifold vacuum is high. If operating conditions exceed system capacity (badly worn engine, sustained heavy load, etc.), the system is designed to allow excessive amounts of blowby to back flow through the crankcase vent tube into the air cleaner to be consumed by normal combustion.