Positive Crankcase Ventilation: Description and Operation

This system is used to prevent blow-by gasses from entering the atmosphere and incorporates a positive crankcase ventilation (PCV) valve installed in the rocker arm cover.
The system supplies fresh air to the crankcase through the air cleaner. Once inside the crankcase, the fresh air is mixed with blow-by gasses. This mixture then passes through the metered orifice of the PCV valve into the induction system where it is burned in the combustion process. Under heavy acceleration or high speed driving, manifold vacuum decreases and blow-by gasses exceed the capacity of the PCV valve. These gasses then back up into the air cleaner through the breather hose.

Testing

1. Remove PCV valve from rocker arm cover. A hissing noise should be heard and a strong vacuum should be felt when a finger is placed over the valve inlet.
2. Disconnect ventilation hose, then remove PCV valve. Blow through threaded end of valve. Air should pass through valve easily.
3. If steps 1 and 2 reveal a restricted ventilation system, clean hose and/or valve with ethylene alcohol or equivalent.