Kraftstoffpumpensteuerung

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"Fuel Pump Relay: Description and Operation

When the key is first turned "ON," without the engine running, the ECM will turn the fuel pump relay "ON" for two seconds. This builds up the
fuel pressure to normal operating pressure. If the engine is not started within two seconds, the ECM will shut the fuel pump "OFF" and wait until ignition reference pulses are present. As soon as the engine is cranked, the ECM turns the relay "ON," which powers the fuel pump.
As a back-up system to the fuel pump relay, the fuel pump can also be turned "ON" by the oil pressure switch. The oil pressure switch is a normallyopen switch which closes when oil pressure reaches about 28.0 kPa (4.0 psi). If the fuel pump relay fails, the oil pressure switch will power the fuel pump.

- A faulty fuel pump relay can result in long cranking times, particularly if the engine is cold.
- An inoperative fuel pump would cause a no start condition. A fuel pump which does not provide enough pressure can result in poor
performance."