A crankcase ventilation system is used to consume crankcase vapors in the combustion process instead of venting the vapors into the atmosphere. Fresh air from the throttle body is supplied to the crankcase, mixed with blow by gases, and then passed through a PCV valve into the intake manifold.

The primary control is through the positive crankcase ventilation (PCV) valve (3) which meters the flow at a rate depending on the inlet vacuum (1). To maintain idle quality, the PCV valve restricts the flow when the inlet vacuum is high. If abnormal operating conditions arise, the system is designed to allow excessive amounts of blow-by gases to backflow through the crankcase vent into the throttle body to be consumed by normal combustion.

A plugged valve may cause the following conditions:

A leaking valve would cause:

If an engine is idling rough, check for a plugged PCV valve. Replace the valve if required. Use the following procedure:

1. Remove the PCV valve from the intake manifold.
2. Shake the valve and listen for the rattle of the needle inside the valve.
3. If valve does not rattle, replace the valve.

With this system, any blow-by in excess of the system capacity from a badly worn engine, sustained heavy load, etc., is exhausted into the intake manifold and drawn into the engine.

Proper operation of the crankcase ventilation system is dependent upon a sealed engine. If oil sludging or dilution is noted, and the crankcase ventilation system is functioning properly, check the engine for a possible cause and correct the condition to ensure that the system will function as intended.