Positive Crankcase Ventilation: Description and Operation

Blow-by Flow:

Air Induction:

PURPOSE
A Positive Crankcase Ventilation ([1][2]PCV) system is used to provide more complete collection of crankcase vapors. Fresh air from the air cleaner is pulled into the crankcase, mixed with blow-by gases and then purged through a PCV valve into the intake manifold.

OPERATION
The primary control is through the PCV valve, which meters the flow at a rate dependent upon manifold vacuum. To maintain idle quality, the PCV valve restricts the flow when intake manifold vacuum is high. If abnormal operating conditions arise, the system is designed to allow excessive amounts of blow-by gases to back flow through the crankcase vent tube into the air cleaner to be consumed by normal combustion.