See Figures 1, 2 and 3
For more information on the Positive Crankcase Ventilation (PCV) system please refer to Emission Controls in this repair guide.
The PCV valve system vents crankcase gases into the engine air/fuel intake system where they are burned with the air/fuel mixture. The PCV valve system keeps pollutants from being released into the atmosphere, and also helps to keep the engine oil clean, by ridding the crankcase of moisture and corrosive fumes. The system consists of the PCV valve, its mounting grommet, the nipple in the air intake and the connecting hoses. On most applications the system contains some form of oil separator to remove oil from the vapors.
Because of the function this system serves in keeping the crankcase ventilated, it is extremely important the valve be checked periodically and replaced if clogged. A restricted PCV valve will allow pressure to build in the crankcase, which can decrease gas mileage, cause gasket oil leaks and most importantly allow the build-up of dangerous oil sludge/acids.
The PCV valve should be replaced at a minimum of every 60,000 miles (96,000 km). In addition, the late model 5.0L engines have a filter element located in the intake manifold, just beneath the PCV valve mounting grommet (early models had a PCV valve which was mounted in the valve cover and not the intake manifold). When equipped with the manifold mounted valve, this crankcase emission filter element should be replaced every 30,000 miles (48,000 km). Of course, as-long-as you are removing the PCV valve for access to the element, it is a good time to check and/or replace the valve as well.
For details concerning PCV system component testing or replacement, please refer to Emission Controls of this repair guide.