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I have a 2016 RV12 with a Rotax 912-ULS, with the higher pressure auxiliary electric fuel pump.  Prior to start, the electric pump pressure was always around 4.5 psi, and after start it would go up to 5.1 to 5.6 psi.  After a Condition Inspection last week, now prior to start the fuel pressure was 5.6 psa, and after start, the fuel pressure dropped to 4.5 psi.  At this point, I was not sure the mechanical pump was working (did not think to pull the fuse).  I went ahead and taxied out, did my runup, then shutdown the engine. Now the electric pump fuel pressure read 4.5 psi.  I started the engine, and the fuel pressure went up to between 5.1 and 5.5 psi.  Back to the increase of pressure after start.

I have always believed the fuel pressure had to go up which indicated the mechanical pump was good.

What should really happen?  Does it matter if the fuel pressure goes up or down?  According to Vans, though the person said he was not sure, he said it made sense that it would go down.

I thought the POH said to check that there was an increase, but it does not.

Thoughts????

Bob

  • Re: 912-ULS Fuel Pressure After Start

    by » one month ago


    I would not worry about it, sometimes it just fluctuates and this has been discussed many times on this forum but has never really been resolved.


    Thank you said by: Bob Jones

  • Re: 912-ULS Fuel Pressure After Start

    by » one month ago


    Thanks for the quick reply.  I have been reading the articles for the past year, but this one seems different.  We have been through the erratic pressures, and they have leveled out and have been pretty solid for the past month.  This was the first time in over a year I have seen a higher pressure before start and lower after start, but well within range.

    I guess I will monitor it and see what happens.  Timing is a little funny as it happened after getting the plane back from a Condition Inspection.

     

    Thanks again.

    Bob


  • Re: 912-ULS Fuel Pressure After Start

    by » one month ago


    During the inspection did they replace the fuel filters?

    The filters may be "Wonky" until they completely wet out and the trapped Air clears.


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


    Thank you said by: Bob Jones

  • Re: 912-ULS Fuel Pressure After Start

    by » 6 weeks ago


    Bob,  From the descriptions you presented, I am leaning toward an air gap in the system which your electric fuel has taken care of after your engine shutdown after that taxi.  I wouldn't worry about looking for faults because it densest seem that you have any.

    Safe flying!

    Andre'

     


    Thank you said by: Bob Jones

  • Re: 912-ULS Fuel Pressure After Start

    by » 6 weeks ago


    many RV12's seem to have a low psi on takeoff and so do some other low wings like Sling. Remember we are reading tenths  to just 1-2 psi so I wouldn't overly worry unless it drops below minimum standards or shoots way up over the max. Many times it's the pressure sensor and or a bad ground to the sensor. I don't think I'd worry too much if all it does is change a psi or so between start, taxi and flight. You can always put in a mechanical gauge in line and see if it matches the digital on.

     


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-574-1080 Home (TRY HOME FIRST)
    520-349-7056 Cell

    Thank you said by: Bob Jones

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