PCV system diagram
General description
1. A positive crankcase ventilation system reduces harmful exhaust emissions by circulating fresh air through the crankcase to pick up the slack from gases that are misdirected through the intake manifold and would be burned in the engine.
2. The main components of this system are vacuum hoses and the PCV valve, which regulates the flow of gases according to engine speed and manifold vacuum.
Examination
3. The PCV system can be quickly and easily tested to ensure proper operation. This system should be checked regularly as carbon and soot from the gases will eventually clog the PCV valve and/or system hoses. When PCV flow is reduced or stopped, common signs include a rough idle or a decrease in engine speed while idle.
4. To check for proper vacuum in the system, remove the top air cleaner plate and position the small PCV filter on the inside of the air cleaner housing.
5. Disconnect the pipe to this filter.
6. With the engine idling, place a large pressure washer 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 completely 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 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. Turn off the engine and install the PCV valve. Gently pull it away from the rubber sealing ring. Shake it and listen for a clicking sound. These are the locking balls rolling. 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 for suction. This will be a relatively strong vacuum that will be immediately felt. See also Section 1, Chapter 31.
10. If little or no vacuum is felt at the PCV valve, turn off 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 corresponding vacuum hose or inlet in the engine is engaged. 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 passage in the carburetor or manifold requires the assembly to be removed and completely cleaned to remove the carbon buildup. A strong vacuum senses the PCV valve's entry, but a small or no vacuum from the valve indicates a faulty PCV valve and requires replacement with a new one.
11. When purchasing a new PCV valve, make sure it is for your engine. An incorrect PCV valve can produce too little or too much vacuum, possibly causing engine damage.
Replacement of parts
12. The procedures for replacing the PCV valve and filter are described in Section 1.