Positive Crankcase Ventilation

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The Positive Crankcase Ventilation (PCV) system is used to provide more effective elimination of crankcase vapors. Fresh air from the air filter housing or throttle body is supplied to the crankcase where it is mixed with blow-by gases and passed through a PCV valve into the intake manifold or supercharger inlet (3.8L VIN 1). This mixture is then passed into the combustion chamber and burned. See Fig 1.

The PCV valve provides primary control in this system by metering the flow of the blow-by vapors, according to manifold vacuum. When manifold vacuum is high (at idle), the PCV restricts the flow to maintain a smooth idle condition.

Under conditions in which abnormal amounts of blow-by gases are produced (such as worn cylinders or rings), the system is designed to allow the excess gases to flow back through crankcase vent hose into the intake or throttle body to be consumed during normal combustion.

Fig 1: Identifying PCV System

Courtesy of GENERAL MOTORS CORP.