Positive Crankcase Ventilation Valve: Testing and Inspection

Fig. 17 Positive crankcase ventilation:

This system, Fig. 17, prevents blowby gases produced during the combustion process from entering the atmosphere. This is accomplished by scavenging the blowby gases in the crankcase and routing them into the intake system where they are burned along with the normal air fuel mixture. In addition to controlling the emission of crankcase vapors, this system continuously ventilates the crankcase with fresh air which aids in the prevention of sludge.

During engine operation, manifold vacuum controls the airflow through the PCV system. When manifold vacuum is relatively high, such as at idle or at cruising speed, fresh air is drawn through the air inlet filter into the crankcase. After circulating through the crankcase, the vapor laden air is drawn through the PCV valve, and into the intake system. The vapor mixes with the air fuel mixture and is burned in the combustion chambers. The PCV valve is calibrated to control airflow at a rate acceptable to the intake system.

If crankcase vapor pressure exceeds the flow capacity of the PCV valve, airflow in the system reverses. Crankcase vapor is then drawn through the air cleaner element and into the intake system.

DIAGNOSIS

PCV VALVE
Remove PCV valve from rocker cover. Shake valve, valve should rattle when shaken. If not, PCV valve is sticking and should be replaced.

PCV SYSTEM CHECK
1. Start engine and allow to reach normal operating temperature.
2. Remove PCV valve from cover.
3. Hold valve in vertical position and feel for vacuum. If vacuum is present, system is operating properly. If vacuum is not felt, system is plugged. Correct by replacing PCV valve and/or hoses or cleaning out passages.