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350SLC, 500SLC, 300TE, 190E2.3 Sportline
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Fuel Pump

On your car the fuel pump should run for about a second when the ignition is switched on and then stop. It should only start to run again when the engine is rotating on the starter or actually running. In the event that the engine stalls (or in the event of an accident) the pump will again stop running. The engine control unit (D Jetronic in your case) operates the fuel pump relay which in turn controls the pump. If your pump operates whenever the ignition is on, the relay may be faulty (welded contacts), the ECU may be faulty (a transistor within the unit provides a path to ground for the external pump relay), or there may be a fault to ground in the wiring between the relay and the ECU.
 
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