Mazda 323/626/929/GLC/MX-6/RX-7 1978-1989

PCV Valve

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See Figure 1

The PCV valve is an emission control device operated by intake manifold vacuum to prevent crankcase blow-by gases from escaping into the atmosphere. When the engine is running at idle, the valve opens slightly to allow a small amount of blow-by gas to be drawn into the intake manifold/dynamic chamber where it mixes with intake air for combustion in the cylinders. As engine speed increases, the valve opens to allow more of the blow-by gases into the chamber.

TESTING



1978-82 GLC and 1979-82 626
  1. With the engine idling and fully warmed up, unclamp and remove the hose leading to the PCV valve at the valve.
  2.  
  3. Place your finger over the open end of the hose to stop airflow. If the idle speed drops, the valve is working properly and should be reinstalled. If the idle speed does not change, replace the valve.
  4.  

Except 1978-82 Models and RX-7

See Figure 2

  1. Warm up the engine and allow it to run at idle speed.
  2.  
  3. Disconnect the PCV valve with the ventilator hose from the valve cover.
  4.  



Click image to see an enlarged view

Fig. Fig. 1: Flow of air and gases in a gasoline piston engine PCV system



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Fig. Fig. 2: Checking the PCV valve-except RX-7 and all 1978-82 models

  1. Cover the valve opening with your finger and listen for a change in the idle speed.
  2.  
  3. If the idle speed drops, the valve is working properly and should be reinstalled. If the idle speed does not change, replace the valve.
  4.  

RX-7

See Figure 3

Since rotary engines are not equipped with a PCV system, there is no inspection or replacement procedure for a PCV valve. Instead, blow-by gases in the crankcase are kept from being released into the atmosphere by a ventilation and check valve on 1979-80 models, or by a check and cut valve on later models. (Testing and replacement information on these valves appears in Driveability & Emissions Controls .)



Click image to see an enlarged view

Fig. Fig. 3: Location of the ventilation and check valve on 1979-80 RX-7 models. Arrows indicate the flow of blow-by gases while the engine is running.

REMOVAL & INSTALLATION



Except RX-7

See Figure 4

  1. Remove the air cleaner assembly on carburetor equipped models.
  2.  
  3. If so equipped, remove the clip fastening the hose to the outer end of the PCV valve, then pull the hose off the valve.
  4.  



Click image to see an enlarged view

Fig. Fig. 4: Disconnect the ventilator hose, then remove the PCV valve

Although 1983 and newer models typically use a PCV valve which mounts in a valve cover grommet, most models prior to 1983 use a threaded PCV valve which screws into the intake manifold. Such PCV valves have a hex head section which permits the use of an ordinary open end wrench, deep well socket, or factory tool 49-1011-120 to remove or install the valve.

  1. Rotate and pull the PCV valve from the valve cover grommet or unscrew the valve from the intake manifold, as applicable. Be careful to retain the washer used on some GLCs, if so equipped.
  2.  
  3. Installation is the reverse of removal. Make sure that both ends of the valve are properly seated, and replace any of the ventilator hoses if they are cracked.
  4.  

 
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