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Home >> Mercedes Benz >> 1991 >> 560SEC >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests >> Fuel Control System >> Start Valve (420SEL & 560 Series)
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Start Valve (420SEL & 560 Series)

  1. With ignition off, disconnect coolant temperature sensor. Install 2500-ohm resistor between CTS connector terminals No. 2 and 4 to simulate 68°F (20 °C). Unplug Green cable on ignition switching unit (located on firewall). Disconnect start valve connector and connect voltmeter across terminals of cold start valve connector. Crank engine, noting voltage reading. Voltage should be about 10 volts for about 9 seconds. If voltage is about 10 volts, test is complete. If voltage is not about 10 volts, go to next step.
  2. Check wiring for continuity from start valve connector to fuel pump relay, and check connector ground wire to engine. Resistance should be zero ohms. If resistance is not about zero ohms, repair open circuit and go to next step. If resistance is okay, test is complete.
  3. With coolant temperature sensor connector still jumped and Green cable still disconnected. Connect voltmeter between fuel pump relay connector terminal No. 2 and engine ground. Crank engine (but it should not start). Voltage reading at terminal No. 2 should be 3.5-5.0 volts. If not to specification, repair wiring circuits. If voltage is okay, replace fuel pump relay.
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