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

  1. Connect vacuum tester between EGR valve and switch-over valve. Disconnect connecting rod on ball head. Start engine and run at about 1300 RPM. Place adjusting roller (916 589 00 21 00) on vacuum control valve and move lever against stop. Check vacuum reading.
  2. If vacuum reads 5.3-6.4 in. Hg, proceed to step 3  ). If reading is above or below this value, check orifice for obstruction. If vacuum reading was too low, install a smaller orifice. If this does not increase vacuum, or if reading was too high and Yellow orifice is installed, replace vacuum control valve.
  3. Pull off central plug. Connect test line between tapping point on Black orifice and valve plate connection. Connect vacuum tester to port 3 on central plug. Start engine and read vacuum. If vacuum does not drop, replace switch-over valve. If vacuum is 18.8-21.5 in. Hg at idle, and zero when regulating linkage is moved to full throttle stop, stop engine.
  4. Vacuum should remain constant for about 2 minutes. If not, replace switch-over valve. If vacuum holds, remove connections and proceed to step 5  ).
  5. Connect vacuum tester between EGR valve and switch-over valve. Operate vehicle on a dynamometer or road, but not at full throttle. Read vacuum. If there is no vacuum above 40 MPH, and vacuum is present below 40 MPH, system is okay and test is finished. If vacuum does not drop at speeds above 40 MPH, proceed to step 6  ).
  6. Connect voltmeter to plug of switch-over valve and drive vehicle. If about 12 volts are present at speeds above 40 MPH, check electrical wiring and components and replace any defective parts. If there is no voltage, replace switch-over valve.
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