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

  1. With engine at operating temperature, disconnect coolant temperature sensor. Connect 2.5 k/ohm test resistor to simulate 68°F (20°C). Disconnect vacuum line from side connection of switchover valve and connect vacuum tester with "Y" fitting. Go to step 2).
  2. Start engine. Disconnect suction hose at air pump filter and close with finger. Air pump should be running and vacuum should be about 20 in. Hg. Suction should be felt at end of hose to air pump. If not okay, go to step 4). If okay, go to step 3).
  3. The air pump must disengage after about one minute and the vacuum drop to zero. If not okay, unplug air injection relay. If vacuum drops, replace air injection relay. If vacuum doesn't drop, check routing of vacuum lines and switchover valve. Repair or replace components as necessary.
  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 No. 3 and terminal No. 1 at plug. Voltage should be 12 volts. If not okay, check power supply. If okay, replace air injection relay. End of test.
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