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Had my first successful (smooth) start today!  I also had a warning come up showing high fuel pressure after start (53 psi).  Pre-start, if I run a single fuel pump I'll see a steady 48 psi and with both pumps running, I see 52-53 psi.  I started with a single pump and ran with the same throughout my run test today and immediately after starting, the fuel pressure jumps to 53 psi and holds steady.  If I switch pumps, the pressure stays the same.

 

This was a full fuel kit (fuel line, filter, fuel bypass, etc.) that came from the boys at Skytek Air.  What I'm wondering is if the bypass orifice doesn't need opening up a bit but I'm not sure where to start other than on this forum.  Install is standard as per Rotax installation manual, uses a Bosch filter, which was recommended prior to Rotax issueing their own filter.  Anyone else experience this and if so, how was it resolved?

 

Thanks!

 

Tim

  • Re: High Fuel Pressure After Start

    by » one month ago


    So I may have jumped the gun here.  Looks like other threads recommend taking a manual pressure reading to ensure the sensor is calibrated properly.  I'll do that first and report back to this thread.  I'm using the Stock Flight Systems EMU with the Rotax issued fule sensor (664365).  It looks like the EMU supports a fuel pressure offset adjustment so I'll verify with an analog pressure gauge first and make changes if required.

     

    Tim

     


  • Re: High Fuel Pressure After Start

    by » one month ago


    The Bypass Orifice has nothing to do with the fuel pressure.
    You could eliminate the bypass and the fuel pressure will not change.

    The fuel pressure regulator controls the pressure at 3 bar (~44psi) above (Differential) the Airbox(MAP) pressure.
    If the Fuel RETURN (Not the BYPASS) Hose is restricted, the measured fuel pressure will increase.
    If the Fine fuel filter is restricted, the measured pressure will increase.

    Measure the Fuel pressure before the Fine Fuel Filter and at the Fuel Manifold Input.
    Both should be within 1 psi of each other with a New, Clean, Fine Fuel Filter.

    A Mechanical Pressure Gauge should indicate a fuel pressure of ~35 psi (Gauge) with the engine at idle.

    The numbers you are seeing are consistent with an ABSOLUTE Fuel pressure measurement.
    The Fuel pressure needs to be a DIFFERENTIAL Measurement.

     

     


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


    Thank you said by: Tim

  • Re: High Fuel Pressure After Start

    by » one month ago


    You just got to love Bill. He has some great info.


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: High Fuel Pressure After Start

    by » one month ago


    Thanks for he recommendation and I'll try that today if I can  find a test gauge in town.  If not, I'll need to order something online.  Any suggestions of the fuel pressure test kit to get?

     

    Also, spoke with Michael Stock at Stock Flight Systems as this is the EMU I'm using.  He had me measure the voltage across the sensor connectors and it would appear I'm getting a slightly higher voltage than normal on the output contact (2.2 volts at 1 Bar ambient).  At least that was my interpretation from the voltage vs pressure chart he sent me.  My interpretation may be all wrong so I'm waiting to hear back from Michael.  I did play with the offset on the EMU yesterday and verified I can make adjustments to get the numbers within the proper range but obviously I need to know what the 'actual' pressure is before doing this.

     

    Thanks!


  • Re: High Fuel Pressure After Start

    by » one month ago


    The test gauge is nothing special.
    You can Redneck it out or Hardware and Auto Parts store Pieces/Parts.
    Any 100psi Gauge and a few odd fittings to tap into your lines will do the job.


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


    Thank you said by: Tim

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