The Positive Crankcase Ventilation (PCV) valve regulates the release of crankcase vapors during various engine operating conditions. As the engine operates, some combustion gas will escape from the cylinder by passing the piston rings. These gasses accumulate in the oil pan. Since a small amount of vapor is added on every piston stroke, the pressure within the oil pan quickly builds. If these vapors are not allowed to escape through a planned path they will quickly find their own exit, usually by forcing a hole in an engine gasket.
Since the gasses contain hydrocarbons and other pollutants, they cannot simply be vented to the atmosphere. The PCV valve allows the release of the vapors under controlled conditions back into the intake air stream. The vapors are then mixed with the incoming air, reintroduced to the combustion chamber and reburned. At high vacuum (idle speed and partial load range) the PCV will open slightly and at low vacuum (full throttle) it will open fully. This causes vapor to be removed from the crankcase by the engine vacuum and then sucked into the combustion chamber where it is dissipated.
Most of the cars covered in this guide simply use a hose from the valve cover to the air intake to route the vapors into the engine; the computer controlled fuel injection deals with the presence of the vapors automatically. If your car has a 3S-fe engine, it does not have a PCV valve, but the hose and passages must still be checked and cleaned periodically.
REMOVAL & INSTALLATION
- Check the ventilation hoses for leaks or clogging. Clean or replace as necessary. Vapor passage in the ventilation lines is controlled by two orifices. Inspect the hoses for cracks, leaks or other damage. Blow through the orifices to make sure they are not blocked. Replace all components as necessary.
- Locate the PCV valve in the valve cover or from the manifold-to-crankcase hose and remove it.
- Blow into the crankcase end of the valve. There should be free passage of air through the valve.
- Blow into the intake manifold end of the valve. There should be little or no passage of air through the valve.
- If the PCV valve failed either of the preceding two checks, it will require replacement. Do NOT attempt to clean the valve.
- Install the valve, making sure it is not backwards. Connect the hoses and make certain they are not twisted or kinked.