Positive Crankcase Ventilation: Description and Operation

PCV Flow:

PCV Hose:

PURPOSE
A Positive Crankcase Ventilation ([1][2]PCV) system is used to prevent blow-by gases from escaping to the atmosphere by routing them through a vacuum controlled ventilation valve, into the intake manifold. Fresh air from the air cleaner is pulled into the crankcase, mixed with blow-by gases and then combined with the air/fuel mixture and are burned in the combustion chamber.

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.

SYSTEM FAULTS
A plugged PCV valve or hose may cause:
^ Rough idle.
^ Stalling or slow idle speed.
^ Oil leaks.
^ Oil in air cleaner.
^ Sludge in engine.

A leaking valve or hose could cause:
^ Rough idle.
^ Stalling.
^ Erratic idle speed.