Mazda 323/MX-3/626/MX-6/Millenia/Protégé 1990-1998 and Ford Probe 1993-1997

Exhaust Gas Recirculation System

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OPERATION



See Figure 1

The Exhaust Gas Recirculation (EGR) System introduces exhaust gas into the intake manifold which reduces the NOx content in the exhaust gas. The system utilizes a control valve, a modulator valve, the engine control unit, a solenoid valve, throttle sensor and a water thermosensor.



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Fig. Fig. 1: Typical EGR system schematic

TESTING



EGR System
  1. Start the engine.
  2.  
  3. Accelerate the engine and verify that the EGR control valve diaphragm does not move upon acceleration with the engine cold.
  4.  
  5. Continue to run the engine until it reaches the normal operating temperature.
  6.  
  7. Accelerate the engine and verify that the EGR control valve diaphragm moves upward upon acceleration with the engine warm.
  8.  

EGR Valve

See Figures 2 and 3

  1. Manually operate the valve by pushing on the diaphragm with a finger.
  2.  



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Fig. Fig. 2: Press on the underside of the EGR valve diaphragm to check for proper movement and resistance

  1. There should be spring resistance felt and the diaphragm should not stick or bind.
  2.  
  3. Start the engine and allow it to reach normal operating temperature.
  4.  
  5. Attach a vacuum pump to the valve and apply vacuum.
  6.  
  7. The engine should begin to run rough or stall as the vacuum increases.
  8.  



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Fig. Fig. 3: With the engine running, apply vacuum to the EGR valve with a vacuum pump and verify a change in engine rpm

  1. If there is no change in the engine speed, turn the engine OFF .
  2.  
  3. Apply at least 5.91 in.Hg (50mmHg) of vacuum to the valve to check for a bad diaphragm. The vacuum should stay at the same reading. If it does not, or you are not able to achieve a vacuum, replace the EGR valve.
  4.  
  5. If the vacuum did not bleed off, remove the valve and check the passages for blockage. Clean as necessary.
  6.  

EGR Modulator Valve

See Figure 4

  1. Remove the EGR modulator valve assembly.
  2.  
  3. Plug the number 1 port and attach a vacuum gauge to the number 3 port as shown.
  4.  



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Fig. Fig. 4: Test the EGR modulator using a hand vacuum pump

  1. Blow air into the exhaust port and operate the vacuum pump. Make sure that vacuum is held.
  2.  
  3. Release the plug from the exhaust port and make sure that the vacuum pressure is released.
  4.  
  5. If vacuum pressure is not held or released as required, replace the EGR modulator valve assembly.
  6.  

EGR Solenoid Valve
dual port valve
  1. Label and disconnect the vacuum hoses from the solenoid valve.
  2.  
  3. Detach the solenoid valve electrical connector.
  4.  
  5. As shown, blow air through the solenoid valve from vacuum port A and make sure that air flows out of port B.
  6.  
  7. Apply 2 volts and a ground to the valve at the electrical connector point.
  8.  
  9. Blow through the vent hose and make sure that the air flows.
  10.  
  11. Replace the solenoid valve if the valve is not as specified.
  12.  

three port valve
Vent Side
  1. Label and disconnect the vacuum hoses.
  2.  
  3. Blow through the vent hose and make sure the air flows.
  4.  
  5. Detach the solenoid valve electrical connector.
  6.  
  7. Apply 2 volts and a ground to the valve at the electrical connector point.
  8.  
  9. Blow through the vent hose and make sure that the air does not flow.
  10.  
  11. Replace the solenoid valve if the valve is not as specified.
  12.  

Vacuum Side
  1. Disconnect the vacuum hoses.
  2.  
  3. Blow through the vent hose and make sure the air does not flow.
  4.  
  5. Detach the solenoid valve electrical connector.
  6.  
  7. Apply 2 volts and a ground to the valve at the electrical connector point.
  8.  
  9. Blow through the vent hose and make sure that the air flows.
  10.  
  11. Replace the solenoid valve if the valve is not as specified.
  12.  

REMOVAL AND INSTALLATION



See Figures 5, 6 and 7

  1. Disconnect the negative battery cable.
  2.  
  3. If necessary, remove the air cleaner assembly.
  4.  



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Fig. Fig. 5: To remove the EGR valve, first disconnect the vacuum hose from the valve



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Fig. Fig. 6: If equipped with two vacuum hoses, make sure to label them. Remove the EGR valve attaching bolts (arrows) ...



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Fig. Fig. 7: ... then remove the valve from the intake manifold as well as the old gasket

  1. If equipped with an EGR position sensor, detach the wire harness connector from the sensor.
  2.  
  3. Some models use a cooling system preheat on the EGR valve, if so equipped, disconnect and plug the water hoses.
  4.  
  5. Disconnect the EGR valve vacuum line. If equipped with more than one hose, label their positions before disconnecting them.
  6.  
  7. If equipped, loosen the exhaust feed pipe retaining nut at the EGR valve and disconnect the pipe. Additional clearance can be gained by also loosening the retaining nut at the exhaust manifold, as well as any pipe retaining clamp bolts.
  8.  
  9. Remove the EGR valve mounting bolts or nuts and remove the valve.
  10.  
  11. Thoroughly clean the gasket mating surfaces.
  12.  
  13. Installation is the reverse of the removal procedure. Use a new gasket when installing the valve.
  14.  

 
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