Mazda B-Series 1998-06

Positive Crankcase Ventilation (PCV) System

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Description & Operation



The PCV valve system vents crankcase gases into the engine air intake where they are burned with the fuel and air mixture. The PCV valve system keeps pollutants from being released into the atmosphere, and also helps to keep the engine oil clean, by ridding the crankcase of moisture and corrosive fumes. The PCV valve system consists of the PCV valve, it's mounting grommet, the nipple in the air intake and the connecting hoses. On some engine applications, the PCV valve system is connected with the evaporative emission system.



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Fig. Cutaway view of the PCV valve and its operation

The PCV valve controls the amount of vapors pulled into the intake manifold from the crankcase and acts as a check valve by preventing air flow from entering the crankcase in the opposite direction. The PCV valve also prevents combustion backfiring from entering the crankcase in order to prevent detonation of the accumulated crankcase gases.

Diagnosis & Testing



  1. Remove the PCV valve from the valve cover or engine block mounting grommet. The PCV valve for the 2.3L and 2.5L engines is mounted in the crankcase oil vent separator in a rubber grommet near the lower intake manifold, or its ventilation hose before the connection to the throttle body. The PCV valve for the 3.0L (B Series Pick-up) and 4.0L engines is mounted in a rubber grommet, installed towards the rear of the left-hand valve cover. On the 2.6L engine, the PCV valve is located at the front of the engine, mounted in a rubber grommet on top of the valve cover. The PCV valve on the 3.0L engine (MPV) is located at the rear of the engine, mounted in a rubber grommet on the right side valve cover.
  2.  
  3. Shake the PCV valve. If the valve rattles when shaken, reinstall it and proceed to Step 3. If the valve does not rattle, it is sticking and must be replaced.
  4.  
  5. Start the engine and bring it to normal operating temperature.
  6.  



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Fig. Check the PCV valve for vacuum at idle

  1. Disconnect the closure (fresh air) hose from the air inlet tube (connects the air cleaner housing to the throttle body).
  2.  
  3. Place a stiff piece of paper over the hose end and wait 1 minute.
    1. If vacuum holds the paper in place, the system is OK; reconnect the hose.
    2.  
    3. If the paper is not held in place, check for loose hose connections, vacuum leaks or blockage. Correct as necessary.
    4.  

  4.  

Removal & Installation



  1. Disconnect the vacuum hose from the PCV valve.
  2.  
  3. Remove the PCV valve from its mounting grommet.
  4.  



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Fig. PCV system hose routing for the 2.3L engine-2.5L engine similar



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Fig. PCV valve and hose location for the 2.6L engine



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Fig. PCV system hose routing for the 3.0L engine (B Series Pick-up)



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Fig. PCV system hose routing for the 4.0L engine

  1. To install, attach the PCV vacuum hose to the PCV valve, then insert the valve into its mounting grommet.
  2.  

 
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