Miata 1990-1997

Positive Crankcase Ventilation System

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Positive Crankcase Ventilation Valve



Location

Specific to:

Mazda Miata 1990-1997

The PCV valve is located in a grommet attached to the valve cover.

Click image to see an enlarged view

Fig. The location of the PCV

Operation

Specific to:

Mazda Miata 1990-1997

The PCV system consists of the breather tube and the PCV valve. The breather tube connects the crankcase to a contained fresh air source such as the air cleaner. Air passes into this tube and into the engine after being filtered through a spark arrestor screen in order to prevent a the possibility of an explosion within the engine in the case of a backfire.

Removal & Installation

Specific to:

Mazda Miata 1990-1997

  1. Remove the Positive Crankcase Ventilation (PCV) valve from the valve cover grommet.
  2.  
  3. Disconnect the hose from the PCV valve and remove it from the vehicle.

    Click image to see an enlarged view

    Fig. To remove the PCV valve, first detach the vacuum hose from the valve..



    Click image to see an enlarged view

    Fig. .. then pull the PCV valve from the valve cover grommet

  4.  
  5. Check the PCV valve for deposits and clogging. If the valve rattles when shaken, it is okay. If the valve does not rattle, clean the valve with solvent until the plunger is free, or replace it.
  6.  
  7. Check the PCV hose and the valve cover grommet for clogging and signs of wear or deterioration. Replace, as necessary.
  8.  

To install:

  1. Connect the PCV hose to the PCV valve.
  2.  
  3. Install the PCV valve in the valve cover grommet.
  4.  

Testing

Specific to:

Mazda Miata 1990-1997

Check the Positive Crankcase Ventilation (PCV) valve frequently to see if it is free and not gummed up, stuck or blocked. To check the valve, remove it from the engine and shake it. It should rattle. It is possible to clean the PCV valve by soaking it in a solvent and blowing it out with compressed air. This can restore the valve to some level of operating order.

Click image to see an enlarged view

Fig. Testing the PCV

  1. Warm up the engine to the normal operating temperature and run it at idle.
  2.  
  3. Disconnect the PCV valve together with the ventilation hose from the cylinder head cover.
  4.  
  5. Block the PCV valve opening.
  6.  
  7. Verify that vacuum is felt.
  8.  
  9. Remove the PCV valve
  10.  
  11. Blow through the valve from port A and verify that air comes out of port B.
  12.  
  13. Blow through the valve from port B and verify that no air comes out of port A
  14.  
  15. Replace the PCV valve if necessary
  16.  

 
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