PCV Valve Function
The purpose of the PCV System is to regulate crankcase pressure and ventilate blow-by gases from the crankcase into the intake manifold. The PCV system consists of the positive crankcase ventilation valve, grommet, tube, and an air supply hose. Check around all of these fittings for any signs of oil leakage. Everything must be tight. Oil leakage indicates a possible problem with the system.
The PCV valve uses spring pressure to hold the valve in the open position while the engine is off or when there is a drop in manifold vacuum like upon acceleration. This results in maximum crankcase ventilation. When the engine is at idle and cruise high manifold vacuum pulls the valve upward blocking the port to the intake manifold. This is because manifold vacuum pressure is greater than the PCV valves spring pressure.
A stuck closed PCV valve will cause excessive crankcase pressure resulting in leaks past oil seals and gaskets. Some air supply hoses have an air filter or filament to clean the air entering the crankcase. If the PCV valve is stuck closed blow-by gases will build in the crankcase and oil will travel up the clean air hose and into the air filter. This will result in a contaminated air filter or breather.
A stuck open valve or leaking PCV hose will cause a lean air fuel ratio and driveability issues like surging. When the valve is removed from the valve cover vacuum should be present at its opening. When your thumb is placed over the vacuum leak the plunger should "snap back" into the valve. When removed the PCV valve should rattle when shaken. Please note that if the valve does not rattle when shaken, it is sludged and must be replaced. Failure of this valve is typically due to a lack of vehicle maintenance and in particular regular oil changes. This old oil results in sludge and jelled engine parts.
