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

Exhaust Gas Recirculation System-Gasoline Engines

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OPERATION



This system is used to meter a small amount of exhaust gas back into the intake manifold to slow the combustion process, and slightly reduce the maximum temperatures in the combustion chambers, thereby reducing nitrogen oxides. A water temperature switch or three-way solenoid valve may stop exhaust gas recirculation when the engine is cold. On most models, the EGR Control Valve must be serviced periodically, and on some models, a maintenance warning system reset. The EGR valve is by far the most sensitive part of the system, as it can become carbon clogged.

Fuel injected 323s do not utilize an EGR system.

EGR CONTROL VALVE TESTING



See Figure 1

If the EGR system gets clogged or the valve stem seizes due to carbon clogging, the engine may ping even when the proper fuel is used and ignition timing is correct. One way to check the system is to run the engine at idle speed while placing your finger on the EGR valve diaphragm, by reaching in under the housing at the top of the valve. Have an assistant increase the throttle opening. The valve should open and its position should modulate as the throttle is open and closed, adjusting for each engine operating speed and throttle opening variation.



Click image to see an enlarged view

Fig. Fig. 1: Place the tip of your finger as shown to check for EGR valve function

If you doubt that the system is performing properly, the best procedure is to test the EGR valve with the engine at idle and full manifold vacuum applied to the valve diaphragm, as follows:

Except 1988-89 626/MX-6 and 929
  1. Remove the air cleaner assembly.
  2.  
  3. Run the engine at idle.
  4.  
  5. On 1983-84 626 models, plug the hoses of the idle compensator, thermosensor, and reed valves. (Consult the underhood sticker showing vacuum hose routing to identify these).
  6.  
  7. Disconnect the vacuum sensing tube from the EGR control valve, and make connections directly to an intake manifold tap (not to the carburetor) with a vacuum hose.
  8.  
  9. Connect this vacuum tube to the EGR control valve. The engine should suddenly run very roughly or stall. If it does not, clean or replace the EGR control valve.
  10.  

1988-89 626/MX-6 and 929
  1. Grasp the rod of the EGR control valve or apply pressure to the spring diaphragm, to make sure that it moves freely up and down and that there is resistance from the actuating spring.
  2.  
  3. Disconnect the vacuum hose from the EGR control valve and connect a vacuum pump to the valve.
  4.  
  5. Start the engine and run it at idle speed. Apply vacuum to the valve. Check that the engine runs roughly or stalls when 1.6-2.4 in. Hg (40-60mm Hg) of vacuum is applied to the valve.
  6.  
  7. If the engine does not behave as described with the specified amount of vacuum applied, replace the EGR control valve.
  8.  

EGR VALVE POSITION SENSOR TESTING



1985 626

See Figure 2

Disconnect the position sensor connector, which leads to the bottom of the EGR valve. Connect an ohmmeter as shown. If there is an open circuit, the position sensor is defective and the EGR valve should be replaced. If there is resistance, the sensor may be presumed to be okay.



Click image to see an enlarged view

Fig. Fig. 2: Hook up an ohmmeter to the EGR valve position sensor connector as shown-1985 626

EGR MODULATOR VALVE TESTING



You will need a source of vacuum such as a vacuum pump and a vacuum gauge to make these tests. You may be able to disconnect and plug off the hoses leading to this valve, then operate the engine and use engine vacuum to make the tests. In this case, you can tee a vacuum gauge into the line which will apply vacuum.

1986-87 323
  1. Note the routing of all hoses leading to the modulator valve, especially the hose which is connected to the exhaust side of the EGR valve. Remove the EGR Modulator valve. Plug the No. 1 port, then attach a source of vacuum to the No. 3 port.
  2.  
  3. Attach a clean hose to the exhaust gas port. Blow into the end of the hose and maintain pressure. Apply vacuum to the No. 3 port, then seal off the source of vacuum. Vacuum should be maintained as long as air pressure is applied.
  4.  
  5. Stop applying air pressure. The vacuum should be released. If the valve fails to respond properly in either Step 2 or 3, replace it.
  6.  

1986-87 626
  1. Note the routing of all hoses leading to the modulator valve, especially the hose which is connected to the exhaust side of the EGR valve. Remove the valve. Plug the ports numbered 2 and 3 . Attach a source of vacuum to the No. 1 port.
  2.  
  3. Attach a clean hose to the exhaust gas port. Blow into the end of the hose and maintain pressure. Apply vacuum to the No. 1 port, then seal off the source of vacuum. Vacuum should be maintained as long as air pressure is applied.
  4.  
  5. Stop applying air pressure. The vacuum should be released. If the valve fails to respond properly in either Step 2 or 3, replace it.
  6.  

VACUUM DELAY VALVE TESTING



1985 626

You will need a source of vacuum such as a vacuum pump and a vacuum gauge to make these tests. You may be able to disconnect and plug the hoses leading to this valve, then operate the engine to produce vacuum for testing. In this case, you can tee a vacuum gauge into the line which will apply vacuum. You will also need about four feet of vacuum line, the diameter of that used to connect this valve into the system.

  1. Remove the vacuum delay valve. Cut a vacuum hose of the size used to connect this valve into the system to 40 in. (1 meter) in length. Connect the hose to the inlet end of this valve (the arrow on the valve should point away from the hose connection), then attach a source of vacuum and the vacuum gauge to the other end of the hose.
  2.  
  3. Hold your thumb tightly against the open end of the valve. Apply a vacuum of over 20 in. Hg (508mm Hg). Then, seal off the source of vacuum. Release your thumb and watch the gauge as vacuum decreases to 4 in. Hg (102mm Hg). This should take 1.3-2.3 seconds. If the time elapsed during the pressure drop is outside this range, replace the valve.
  4.  

REMOVAL & INSTALLATION



EGR Control Valve
  1. On carburetor-equipped vehicles, remove the air cleaner assembly.
  2.  
  3. Disconnect the vacuum sensing tube from the EGR control valve.
  4.  
  5. Disconnect the EGR control valve-to-exhaust manifold pipe. Disconnect all vacuum hoses.
  6.  
  7. Disconnect the pipe between the EGR control valve and the intake manifold. On the 929, disconnect the two water hoses that are routed in front of the valve and detach the electrical connector.
  8.  
  9. Unbolt and remove the EGR control valve.
  10.  
  11. If the old valve is to be reused, it should be cleaned with a wire brush before installation.
  12.  

To install:
  1. Install the EGR valve with a new gasket. On the 929, fasten the electrical connector and the two water hoses. Connect the EGR valve-to-intake manifold pipe with a new gasket.
  2.  
  3. Connect all vacuum hoses. Connect the exhaust manifold-to-EGR valve pipe.
  4.  
  5. If applicable, install the air cleaner assembly.
  6.  
  7. Start the engine and inspect for exhaust gas leaks. On the 929, check for water leaks also.
  8.  

 
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