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Home >> Mercedes Benz >> 1990 >> 560SEC >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests >> Emission Systems & Sub-Systems >> EGR 420 & 560 Series System Testing

EGR 420 & 560 Series System Testing

  1. Apply about 12 in. Hg to EGR valve. Disconnect vacuum line. The EGR valve should close. If valve does not close, replace EGR valve. If okay, go to next step.
  2. Run engine at idle speed. Apply about 12 in. Hg to EGR valve. Engine should run rough at idle. If engine does not run at idle, replace EGR valve. If okay, go to next step.
  3. Connect vacuum tester to EGR vacuum line using a "Y" fitting. Increase engine speed slowly to about 4000 RPM. Tester should indicate vacuum. If okay, test is complete. If vacuum is not present, go to next step.
  4. Disconnect vacuum line from thermovalve and connect vacuum tester with "Y" fitting to vacuum line and thermovalve and apply vacuum. Thermovalve should be open with coolant temperature above 122°F (50°C) and closed with coolant temperature below that. If okay, proceed to next step. If valve does not operate as indicated, replace thermovalve.
  5. Test thermovalve for leaks. Seal straight connection of thermovalve. Check and ensure vacuum is held at angular connection to thermovalve. If okay, test is complete. If vacuum is not held, replace thermovalve.
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