A Positive Crankcase Ventilation (PCV) system is used to consume crankcase vapors in the combustion process instead of venting them to the atmosphere. In gasoline engines, a small amount of combustion gases leak past the piston rings into the crankcase. These crankcase blow-by gases contain undesirable hydrocarbon air pollutants. The PCV system is used to prevent these vapors from escaping into the atmosphere, while allowing proper ventilation of the crankcase to maintain good oil quality. Fresh air from the air cleaner is pulled into the crankcase, mixed with blow-by gases and then purged through the Positive Crankcase Ventilation (PCV) valve into the intake manifold.
The primary control is through the PCV valve, which meters the flow rate dependent on intake manifold vacuum.
When intake manifold vacuum is high, during deceleration, low speed driving or idle, the PCV valve controls a low flow rate. This is because during these modes of operation, the crankcase gas levels, including cylinder blow-by, are low.
When intake manifold vacuum is low, such as during acceleration or high load operation, the PCV valve controls flow to a higher rate to accommodate increased engine crankcase gases.
Under full throttle operation or abnormal conditions, such as a worn or damaged engine, or during high speed light load operation, the system allows excess blow-by gases to flow through the fresh air tube into the inlet duct to be combined with incoming air from the air cleaner.
A plugged PCV valve or hose may cause the following conditions:
A leaking valve or hose could cause the following conditions:
PCV SYSTEM TESTING
If an engine is idling rough, check for a clogged PCV valve or plugged hose. Replace system components as required.
- Remove the PCV valve from the rocker cover.
- Run the engine at idle.
- Place your thumb over the end of the valve to check for vacuum. If there is no vacuum at the valve, check for plugged hoses, intake manifold port, or PCV valve. Replace plugged or deteriorated hoses.
- Turn the engine OFF and remove the PCV valve. Shake the valve and listen for the rattle of the check needle inside the valve. If the valve does not rattle, replace it.
REMOVAL & INSTALLATION
- Locate the PCV valve on the valve cover or in the intake manifold.
- Grasp the PCV valve firmly and pull it out of the rubber grommet.
- Once free of the grommet, disconnect it from the vacuum line.
- Inspect the rubber grommet. Replace if necessary.
- Installation is the reversal of the removal procedure.