Positive Crankcase Ventilation: Description and Operation

To reduce HC emissions, crankcase blow-by gas (HC) is routed through PCV valve to the intake manifold for combustion in the cylinders.
The primary control is through the PCV valve which meters the flow at a rate depending on 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 amount of blow-by gases to back flow through the crankcase vent tube into the air cleaner to be consumed by normal combustion.
- A leaking valve or hose would cause:
- Rough idle.
- Stalling.
- High idle speed.




Engine Not Running Or Backfiring




Idling Or Decelerating




Normal Operation