Positive Crankcase Ventilation: Description and Operation

CRANKCASE VENTILATION SYSTEM

Figure 11-1 - Crankcase Ventilation Flow:

A crankcase ventilation system is used to provide more complete scavenging of crankcase vapors. Fresh air from the air cleaner through a filter is supplied to the crankcase, mixed with blow-by gases and then passed through a crankcase ventilation valve into the intake manifold (Figure 11-1).

Figure 11-2 - Crankcase Ventilation Valve Cross Section:

The primary control is through the crankcase ventilation valve (Figure 11-2), which meters the flow at a rate depending on manifold vacuum.
To maintain idle quality, the crankcase ventilation valve restricts the flow when intake manifold vacuum is high. If abnormal operating conditions arise, the system is designed to allow excessive amounts of blow-by gases to back flow through the crankcase vent tube into the air cleaner to be consumed by normal combustion.

CAUTION: An engine can be damaged if it is operated without a crankcase ventilation filter. It is important to perform the "Testing and Inspection" at intervals shown in the vehicle's maintenance schedule. Replace crankcase ventilation components as diagnosis requires.