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Home >> Mercedes Benz >> 1987 >> 560SL >> Repair and Diagnosis >> Engine Performance >> System >> BOSCH Cis-E System >> Component Testing >> EGR System
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EGR System

  1. Apply about 12 in. Hg of vacuum to EGR valve. Disconnect vacuum line. The EGR valve should close. If not okay, replace EGR valve. If okay, go to step 2).
  2. Run engine at idle speed. Apply about 12 in. Hg of vacuum to EGR valve. Engine should run rough at idle. If not okay, replace EGR valve. If okay, go to step 3).
  3. Connect vacuum tester to EGR vacuum line using a "Y" fitting. Increase engine speed slowly to about 2500 RPM. Tester should indicate vacuum. If okay, test is complete. If not okay, go to step 4).
  4. Disconnect vacuum line from thermo valve and connect vacuum tester with "Y" fitting to vacuum line and thermo valve. Increase engine speed slowly to about 2500 RPM. Tester should indicate vacuum. If okay, replace vacuum control valve. If not okay, go to step 5).
  5. Disconnect both vacuum lines from thermo valve. Connect vacuum tester to angular connection of thermo valve and apply vacuum. With engine at operating temperature, thermo valve should be open. If not okay, replace thermo valve. If okay, go to step 6).
  6. Check for vacuum at line from throttle valve housing. There should be no vacuum at idle. If throttle valve is opened (at about 1500 RPM) vacuum should be present. If okay, test is complete. If not okay, correct connection of vacuum lines.
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