Positive Crankcase Ventilation: Description and Operation

Typical PCV System:

PCV Valve:

PURPOSE
The PCV system vents combustion blow-by gases from crankcase into air intake for burning with normal air/fuel mixture. PCV valve automatically regulates ventilation system airflow to air intake as required by engine operating conditions. Valve also prevents backfiring into crankcase.

LOCATION
PCV valve mounted in rubber grommet on valve cover.

OPERATION
PCV valve is operated by pressure differential between crankcase and intake manifold. With no pressure differential (the engine not operating), or when manifold pressure is greater than crankcase pressure, valve is closed. During normal engine operation, valve spring pressure and intake manifold vacuum balance. Air flow quantity then depends on valve position. If valve should become plugged, excess crankcase pressure and vapors are routed back through the ventilation hose and air cleaner assembly into the induction system.