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Home >> Mercedes Benz >> 1986 >> 560SL >> Repair and Diagnosis >> Engine Performance >> System >> Air Injection System >> Testing >> System Check
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System Check

  1. With engine at operating temperature, disconnect coolant temperature sensor plug and connect a 2.5-ohm test resistor to simulate 68°F (20°C). Disconnect vacuum line from side connection of switchover valve. Connect vacuum tester with "Y" fitting. Start engine. Disconnect suction hose to air pump at air filter and close with finger.
  2. The air pump should be running and vacuum present (about 20 in. Hg). Suction should be felt at end of hose to air pump. If okay, go to step 3). If not okay go to step 4).
  3. The air pump should disengage after about 60 seconds and vacuum must drop to zero. If okay, end of test. If not okay, unplug injection relay. Vacuum should drop. If okay, replace air injection relay. If not okay, check routing of vacuum lines and/or switchover valve.
  4. Unplug air injection relay. Check voltage between terminals No. 4 and 5 at plug. Voltage should be about 12 volts. If not okay, check power supply and ground wiring. Check air shutoff valve function and air hoses for proper routing. If okay, go to step 5).
  5. Check voltage between terminal 3 and terminal No. 1 at plug. Voltage should be about 12 volts. If okay, replace air injection relay. If not okay, check power supply.
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