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Home >> Mercedes Benz >> 1982 >> 300SD >> Repair and Diagnosis >> Engine Performance >> Engine Control Systems >> Exhaust Gas RECIRCULATION >> Testing >> 4-Cylinder Engines >> EGR Valve
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EGR Valve

  1. With Yellow orifice installed, connect vacuum gauge between EGR valve and electric switch-over valve. Run engine at idle and note vacuum. If vacuum is present, check all vacuum lines for blockage and proper connection. Connect volt/ohmmeter to plug of switch-over valve and measure voltage. If no voltage, replace valve. If voltage is present, check electrical wiring and components.
  2. If no vacuum in step  1), increase engine speed to 1300 RPM and note vacuum. If vacuum reads 9.4-10.7 in. Hg, stop engine and connect hand vacuum pump to EGR valve and apply 10.7 in. Hg. Pull off vacuum line and EGR valve should be heard to close. If not, replace valve. If it does, proceed to Vacuum Control Check.
  3. If in step  2), no vacuum or low vacuum was noted, check vacuum lines for proper connections and leaks. Disconnect White/Brown line from angled connection of thermo-vacuum valve. Pull White/Purple/Brown line from EGR valve and blow through it. If no air escapes, replace thermo-vacuum valve.
  4. Place hand on switch-over valve and run engine to about 1300 RPM. Valve should noticeably switch. If not, check electrical wiring and components. If it does switch, pull off vacuum line and check for vacuum. If no vacuum, replace switch-over valve.
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