Positive Crankcase Ventilation: Description and Operation

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. 42 Positive Crankcase Ventilation:

During idle speed or partial load conditions, the crankcase vapors get drawn through the oil trap into the throttle housing (downstream of throttle valve). The throttle housing inlet connection is a water heated type. The coolant temperature prevents the icing-up of the PCV breather connection.
During high engine load, the crankcase vapors get drawn through the oil trap into the intake runner (upstream of throttle valve). This vapor hose (PCV hose) section incorporates a safety valve that opens at 0.1 bar (1.5 psi). This safety valve protects the PCV system from engine backfire.
An additional PCV hose is routed from the timing belt housing to the air cleaner, Fig. 42.




COMPONENTS:

OIL TRAP
The air intake system vacuum draws the crankcase fumes into the oil trap. The trap uses a baffle system to separate the heavy oil particles from the vapors. The oil runs back into the crankcase through the bottom exit. The vapors exit at the top of the oil trap.

SAFETY VALVE
The safety valve will open if the pressure in the PCV system exceeds 0.1 bar (1.5 psi). This safety valve protects the PCV system from engine backfire or other system pressures.