1986 Mercedes Benz 560SLFACTORY OEM SERVICE PROCEDURE

EGR System

  1. Apply about 12 in. Hg of vacuum to EGR valve. Disconnect vacuum line. The EGR valve should close (this can be felt). 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 runs 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 must indicate vacuum. If okay, test is complete. If not okay, go to step 4).
  4. Disconnect vacuum line from thermovalve and connect vacuum tester with "Y" fitting to vacuum line and thermovalve. 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 thermovalve. Connect vacuum tester to angular connection of thermovalve and apply vacuum. With engine at operating temperature, thermovalve should be open. If not okay, replace thermovalve. 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.
Fig 1: Overvoltage Relay Plug
G48220
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.