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PCV Valve - Operation And A Source of Boost Leak For Forced Induction

Discussion in 'Engine' started by navylife59, Jan 31, 2011.

  1. navylife59
    Offline

    navylife59 Super Moderator Staff Member

    Joined:
    Mar 22, 2006
    Location:
    Emory, Texas or Gretna, LA
    The PCV (Positive Crankcase Ventilation) valve, by design, does not completely seal (positive seat) against an above atmospheric manifold pressure (backfire or boost pressure). As you can see from the Toyota Tech Pub, testing of the PCV valve demonstrates that there will be some air blowing past the seat.
    PCV Valve Operation.jpg

    INSPECTION
    1. INSPECT VENTILATION VALVE SUB-ASSEMBLY
    (a) Install a clean hose to the ventilation valve.
    (b) Check the ventilation valve operation.
    (1) Blow air into the cylinder head side, and check
    that air passes through easily.
    CAUTION:
    Do not suck air through the valve.
    Petroleum substances inside the valve are
    hazardous to your health.
    (2) Blow air into the intake manifold side, and
    check that air passes through with difficulty.
    If the result is not as specified, replace the
    ventilation valve sub-assembly.
    (c) Remove the clean hose from the ventilation valve.

    Much to the dismay of people running F/I motors, this is an issue for every OEM PCV valve for the majority of factory F/I that I have found so far. A query into the aftermarket resulted in only one item that is reported to have a positive seat for F/I engines. It is offered by RippMods and is in my opinion, way overpriced. I will be looking into a one-way valve or two-way valve (air valves) setup in conjunction with the OEM valve and an appropriate oil catch can. More on this later.
     

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