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I have an 2016 RV12 with the Rotax 912ULS, purchased used at 150 hours, and now have 600 hours.  All along, the fuel pressure has seemed a little erratic with a very rare drop in fuel pressure below 3.0, and normal pressure is 4.0 to 5.5.  

After a recent 100 hour inspection which had the carb floats weighed and the gascolator cleaned out, we now have a consistent low 2.2 psi fuel pressure reading on climb out (with constant low fuel pressure alters) until the power is reduced from full throttle, then the pressure runs fairly constant at 3.5 psi until you start slowing down to land, then the pressure jumps up to 4.5 to 5.5.

We have not put a manual gauge on the fuel line to measure the actual pressure because we can not duplicate the problem on the ground with a full power runup.

Any ideas why we hover at 2.2 psi on takeoff?

Bob

  • Re: 912ULS Low Fuel Pressure on Climb-Out

    by » one month ago


    With a low wing aircraft, you are pumping fuel Uphill when climbing and downhill when descending.

    The fuel pressure will change 1 psi for every 40 inches of rise, not including restriction losses.

    I will ask the rhetorical questions, "Was your AUXillary fuel pump running at the time?"

    And, "Do you have a fuel return line installed?"


    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: 912ULS Low Fuel Pressure on Climb-Out

    by » one month ago


    Van's Aircraft has an optional upgrade that includes a higher pressure fuel pump that helps to address low fuel pressure:

    https://www.vansaircraft.com/service-information-and-revisions/n-2018-07-12/

     


    Thank you said by: Bob Jones

  • Re: 912ULS Low Fuel Pressure on Climb-Out

    by » one month ago


    Bill Hertzel wrote:

    With a low wing aircraft, you are pumping fuel Uphill when climbing and downhill when descending.

    The fuel pressure will change 1 psi for every 40 inches of rise, not including restriction losses.

    I will ask the rhetorical questions, "Was your AUXillary fuel pump running at the time?"

    And, "Do you have a fuel return line installed?"

    Thanks for answering Bill.  Yes, the aux pump was running, and there is a return line.  It just started doing this last week.  One thought is a bad fuel flow sensor, so we ordered a new one, but still waiting for it to come in.  I am not confident that will fix the problem as everything except climb is good.

     

    Bob


  • Re: 912ULS Low Fuel Pressure on Climb-Out

    by » one month ago


    It does not sound like a Pressure sender problem.

    Are you sure that the AUX pump is operating properly?

    Do you see the pressure vary with the pump ON or OFF?


    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: 912ULS Low Fuel Pressure on Climb-Out

    by » one month ago


    I posted here a few months ago, with virtually the same problem. I have yet to get an answer here on the forum, and now a similar issue comes up again. 

    As to my low pressure issue, well, it seems to have disappeared for now. I’m not 100% sure why, as the only differences have been a temperature change, it got warmer here and I found a loose hose clamp when the left card connects to the air box. I noticed soot on the air box sleeve. There are two clamps, it was the clamp at the air box side. I tightened the other three. Could this have caused the problem? 

    At first I thought it was a fuel problem, I primarily use 91 octane NON Ethanol fuel, so I added 100LL, the low pressure readings were still present. 

    As I stated, the issue on climb out has vanished on the few flights I’ve had recently, now that the temps here in the northeast have risen. I’m keeping a close eye on it for now. 


    Thank you said by: Bob Jones

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