When the engine is running, a small portion of the gases which are formed in the combustion chamber will leak by the piston rings, thus entering the crankcase. Since these gases are under pressure they tend to escape the crankcase and enter into the atmosphere. If the gases were allowed to remain in the crankcase for any length of time, they would contaminate the engine oil and cause sludge to build. If the gases were allowed to escape into the atmosphere, they would pollute the air, as they contain unburned hydrocarbons. The crankcase ventilation system recycles these gases back into the combustion chambers, where they are burned.
Crankcase gases are recycled in the following manner. While the engine is running, fresh air is drawn into the engine and mixes with crankcase vapors. Manifold vacuum draws the crankcase vapors up into the intake and they are burned during the engines normal combustion.
The Positive Crankcase Ventilation (PCV) system utilizes a vacuum controlled PCV valve located in the valve cover or the oil filler housing (depending on model). This valve regulates the amount of gases that are recycled into the combustion chamber. At low engine speeds the valve is partially closed, limiting the flow of gases into the intake manifold. As engine speed increases, the valve opens to admit greater quantities of the gases into the intake manifold.
If the valve should become blocked or plugged, the gases will be prevented from escaping the crankcase by the normal route. Since these gases are under pressure, they will find their own way out of the crankcase. This alternate route is usually a weak oil seal or gasket in the engine. As the gas escapes by the gasket, it also creates an oil leak. Besides causing oil leaks, a clogged PCV valve also allows these gases to remain in the crankcase for an extended period of time, promoting the formation of sludge in the engine.
The Closed Crankcase Ventilation (CCV) system operates the same way as a PCV system, however it does not utilize a vacuum controlled valve. A fitting of a calibrated size, referred to as a fixed orifice, meters the amount of crankcase vapors that the engine burns. This fitting can be found located in the valve covers of engines that employ this system. No maintenance is required.
REMOVAL & INSTALLATION
- The PCV valve can be found on the valve cover, except on 4.7 L engines which have it on the oil filler tube.
- To remove a valve cover PCV valve, simply pull it out of the rubber grommet. Disconnect the hose, if required.
- To remove oil filler PCV valve, first disconnect the hose. Rotate the valve CCW until the locating tabs have been freed at cam lock, and then, pull the valve straight out.
- See "DRIVEABILITY AND EMISSION CONTROLS" for PCV valve tests.
- Inspect the inside of the hose. If it is dirty, disconnect it from the intake manifold and clean it with a safe solvent.
- If the PCV valve hose was removed, connect it to the intake manifold.
- Connect the PCV valve to its hose.
- Install the PCV valve into the rubber grommet.