Positive Crankcase Ventilation: Description and Operation

PURPOSE / OPERATION
This system prevents crankcase vapors from entering the atmosphere by scavenging the blow-by gases in the crankcase and routing them into the intake manifold where they are burned along with the normal air/fuel mixture. In addition to controlling the emission of crankcase vapors into the atmosphere, this system continuously ventilates the crankcase with fresh air which aids in the prevention of sludge formation.
Manifold vacuum controls the airflow through the positive crankcase ventilation system. When manifold vacuum is relatively high, such as at idle, or cruising speed, fresh air is drawn through the air inlet filter into the crankcase. After circulating rough the crankcase, the vapor laden air is drawn through the positive crankcase ventilation system, then into the intake manifold. The vapor mixes with the air/fuel mixture and is burned in the combustion chambers. On models equipped, the positive crankcase ventilation valve is calibrated to control airflow at a rate acceptable to the intake system. If crankcase vapor pressure (blow-by), exceeds the flow capacity of the positive crankcase ventilation valve, airflow in the system reverses. Crankcase vapor is then drawn through the air cleaner element and carburetor and burned along with the air fuel mixture.