Schematic of the PCV system
General description
1. The positive crankcase ventilation system reduces the level of harmful exhaust by circulating fresh air through the crankcase to pick up the blow of gases that are misdirected through the intake manifold and be burned in the engine.
2. The main parts of this system are vacuum hoses and a PCV valve that regulates the flow of gases according to engine speed and manifold vacuum.
Examination
3. The PCV system can be quickly and easily checked for correct operation. This system should be checked regularly as carbon and soot from gases will eventually clog the PCV valve and/or system hoses. When the flow of the PCV system is reduced or stopped, the common symptoms are rough idle or a decrease in engine speed at idle.
4. To check for proper system vacuum, remove the air filter top plate and place a small PCV filter on the inside of the air filter housing.
5. Disconnect the pipe to this filter.
6. With the engine idling, place a large dial on the end of the hose. You should feel a slight vacuum. The suction can be heard as soon as your thumb is released. This will indicate that air is being pulled all the way through the system. If there is a vacuum, the system is functioning properly. Check that the filter inside the air filter housing is not clogged or dirty. If it is in doubt, replace it with a new one (contact Section 1).
7. If there is little or no vacuum at the hose end, the system is not clogged and should be inspected further.
8. Shut off the engine and place the PCV valve. Gently pull it away from the rubber sealing ring. Shake it and listen for a clicking sound. These are the fixing balls. If the valve does not click freely, replace it with a new one.
9. Start the engine at idle with the PCV valve removed. Place your thumb on the end of the valve and feel the suction. It will be a relatively strong vacuum that will be immediately felt. see also Section 1, Chapter 31.
10. If there is little or no vacuum in the PCV valve, stop the engine and disconnect the vacuum hose from the other end of the valve. Start the engine at idle and check the vacuum at the end of the hose just disconnected. The absence of vacuum at this point indicates that the appropriate vacuum hose or inlet is on in the engine. If this hose is blocked, replace it with a new one or remove it from the engine and blow it out with compressed air. A clogged port in a carburetor or manifold requires the assembly to be removed and completely cleaned to remove the carbon buildup. A strong vacuum senses the entry into the PCV valve, but little or no vacuum from the valve indicates a broken PCV valve and needs to be replaced with a new one.
11. When buying a new PCV valve, make sure it is for your engine. An incorrect PCV valve can produce too little or too much vacuum, possibly leading to engine damage.
Replacement Parts
12. Procedures for replacing the PCV valve and filter are described in Section 1.