Crankcase vapors and piston blow-by from the engine is removed by intake manifold vacuum. The engine emissions pass through the PCV valve into the intake manifold where they become part of the calibrated air-fuel mixture. They are burned and expelled with the exhaust gases. When the engine cannot supply enough vapor or blow-by gases, make up air is provided by the air cleaner. In this system, fresh air does not enter the crankcase.Positive Crankcase Ventilation (PCV) Valve
See Figures 1, 2 and 3
The PCV valve contains a spring loaded plunger. Based on intake manifold vacuum, this plunger meters the amount of crankcase vapors routed into the combustion chamber. The spring will seat the plunger when the engine is not operating or during engine backfire, which will prevent vapors from flowing through the valve.
High intake manifold vacuum is present when the engine is idling or cruising. During these times, the vacuum is strong enough to completely compress the spring, moving the plunger to the top of the valve which allows minimal vapor flow through the valve.
Maximum vapor flow through the PCV valve is produced during periods of moderate manifold vacuum, when the plunger is only partially pulled away from the inlet.
See Figure 4
- With the engine idling, remove the PCV valve from its attaching point. If the valve is not obstructed, a hissing noise will be heard as air passes through the valve. Also, a strong vacuum should be felt when you place your finger over the valve inlet.
- Turn the engine OFF . Remove the PCV valve from its attaching point, then shake the valve. The valve is OK if a rattling noise is heard as the valve is shaken.
- If any of the previous tests fail, replace the PCV valve and/or hose and retest the system. Do not try to clean and reuse the old PCV valve. It should be replaced with a new one.
REMOVAL & INSTALLATION
For PCV valve removal and installation procedures, refer to General Information & Maintenance of this repair guide.