Positive Crankcase Ventilation: Description and Operation

PURPOSE
The crankcase emission controls prevent crankcase gases from being released into the atmosphere. Instead, the gases are routed to the intake manifold. Crankcase gases are removed from the crankcase by positive crankcase ventilation (PCV). Intake manifold vacuum draws the crankcase gases out of the crank housing into the intake air stream, where they get ignited in the combustion process.

Fig. 40 Positive Crankcase Ventilation:

CONSTRUCTION
A flexible hose connects the crankcase outlet (located center back of engine) to the oil tank.

OPERATION
At idle the intake manifold vacuum draws the fumes from the oil tank to the intake manifold. This line is fitted with a anti backfire valve and a 2mm orifice.
Above idle the fumes are drawn from the oil tank to the air intake runner via a 6mm orifice.
Another breather hose connects the turbo charger oil catch pan with the intake runner for additional crankcase ventilation, Fig. 40.

COMPONENTS:

ANTI BACKFIRE VALVE
The anti backfire valve is used to keep boost pressure, backfire flames and sparks from entering the PCV system.

ORIFICE
The orifice in the vacuum line is calibrated to allow the correct amount of vapors to enter the intake air stream.