• Re: Electrical Problem with Main Fuel Pump

    by » 5 months ago

    This is a 914 Engine.
    It has 2 identical Electrical pumps plumbed in Series/Parallel.
    Neither pump is subordinate to the other.
    The Main/Aux  designation is Arbitrary.

    The Pump designated MAIN Should activate with the MASTER Switch; Not A/B IGNITION Switches.
    The Pump designated AUX should activate with a separate Breaker/Switch.

    Either pump should be capable of supplying at least 150% of the engines fuel needs.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated.

    Thank you said by: Roger Lee, James N Parker

  • Re: Electrical Problem with Main Fuel Pump

    by » 5 months ago

    Why not have the main pump on its own switch, just like the aux?  That way the same one (the "main") doesn't always come on whenever you turn on the Master switch.  There may be times, on the ground, when you want Master power on but no pump running.  And then, once you are in cruise, you can choose either pump to keep running while turning the other off .

  • Re: Electrical Problem with Main Fuel Pump

    by » 5 months ago

    Gents where the 914 is concerned you really should have a look at the circuitry as suggested by Rotax.

    It incorporates some fancy tricks which allow the main pump to continue to run even when your battery or

    main cct breaker are tripped so that if you lose ALL power that pump will continue to run and so will your  engine.

    Oli I know that you fly a gyro, I just dont know which one and if they supply a wiring diagram (few  do).

    If you however follow Bills fault finding process chasing voltages you should find the fault. The trick will be if you 

    have a map (the circuit  wiring diagram) as some manufacturers wrap their wiring looms and make it difficult

    to follow.


    Regards.........Chook. (Western Australia)

  • Re: Electrical Problem with Main Fuel Pump

    by » 4 months ago

    Hi there, I finally found the problem. I followed Bill's advice and checked all items in line. The tricky part was that I mainly checked the impedance with the voltmeter, instead of checking if actually current would come through. The trouble maker was a bad connection at one of the fuses. This means I was checking this fuse 10x or more with the same result: it’s perfectly working and it’s not the problem. Wrong, because what I finally found was that for some stupid reason the cable on one side was not connecting with the fuse. I took it out, made sure that the connection is good and it’s all working perfectly now. Thanks guys, you all were a great help and I do not regret signing up with the Rotax-Forum and becoming a member. Cheers Oli 

    Thank you said by: RotaxOwner Admin, Bill Hertzel

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