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    GM Century/Lumina/Grand Prix/Intrigue 1997-2000

    Crankcase Ventilation System

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    OPERATION



    The Positive Crankcase Ventilation (PCV) system, also referred to as the Crankcase Ventilation (CV) system, is used on all vehicles to evacuate the crankcase vapors. Fresh air from the air cleaner or intake duct is supplied to the crankcase, mixed with blow-by gases and then passed through a Positive Crankcase Ventilation (PCV) valve into the Air Plenum (upper intake manifold).



    Click image to see an enlarged view

    Fig. Cross-sectional view of a typical PCV valve



    Click image to see an enlarged view

    Fig. Common crankcase flow-3.8L (VIN K) engine shown, others similar

    When manifold vacuum is high, such as at idle, the orifice or valve restricts the flow of blow-by gases allowed into the manifold. If abnormal operating conditions occur, the system will allow excessive blow-by gases to back flow through the hose into the air cleaner. These blow-by gases will then be mixed with the intake air in the air cleaner instead of in the manifold. The air cleaner has a small filter attached to the inside wall that connects to the breather hose to trap impurities flowing in either direction.

    A plugged PCV valve, orifice or hose may cause rough idle, stalling or slow idle speed, oil leaks, oil in the air cleaner or sludge in the engine. A leak could cause rough idle, stalling or high idle speed. The condition of the grommets in the valve cover will also affect system and engine performance.

    TESTING



    PCV Valve
    1. Remove the PCV valve. Please see .
    2.  
    3. With the engine at normal operating temperature, run at idle.
    4.  
    5. With the PCV removed from its seat, place a finger over the end to check if vacuum is present. If vacuum is not present, check for plugged hoses or manifold port. Repair or replace as necessary.
    6.  



    Click image to see an enlarged view

    Fig. Check the PCV valve for vacuum at idle



    Click image to see an enlarged view

    Fig. In this application, the PCV valve is mounted in the rear of the intake manifold-3.8L (VIN K) engine



    Click image to see an enlarged view

    Fig. In this application, the PCV valve is mounted in one of the rocker arm covers-3.1L and 3.4L (VIN E) engines



    Click image to see an enlarged view

    Fig. On the 3.4L (VIN X) engine, the PCV valve is mounted in the connection hose



    Click image to see an enlarged view

    Fig. Remove and shake the PCV valve; if a rattling noise is heard, the valve is OK



    Click image to see an enlarged view

    Fig. Exploded view of the PCV valve mounting-3.8L (VIN K) engine



    Click image to see an enlarged view

    Fig. On some vehicles, the PCV valve is mounted in the intake manifold

    1. Stop the engine and remove the valve. Shake and listen for the rattle of the check valve needle. If no rattle is heard, replace the valve.
    2.  

    PCV System
    1. Check to make sure the engine has the correct PCV valve.
    2.  
    3. Start the engine and bring to normal operating temperature.
    4.  
    5. Block off PCV system fresh air intake passage.
    6.  
    7. Remove the engine oil dipstick and install a vacuum gauge on the dipstick tube.
    8.  
    9. Run the engine at 1500 rpm for 30 seconds then read the vacuum gauge with the engine at 1500 rpm.
      1. If vacuum is present, the PCV system is functioning properly.
      2.  
      3. If there is no vacuum, the engine may not be sealed and/or is drawing in outside air. Check the grommets and valve cover or oil pan gasket for leaks.
      4.  
      5. If the vacuum gauge registers a pressure or the vacuum gauge is pushed out of the dipstick tube, check for the correct PCV valve, a plugged hose or excessive engine blow-by.
      6.  

    10.  

     
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