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Aircraft information: RV-12, 912ULS, DYnon D180, 35 hours TT.
Fuel system configuration: 20 gal tank, electric boost pump, FT-60 flow sensor, gascolator, engine driven pump, pressure sensor and return line to tank.

Over the past month I made several cross-country flights, and tweaked the Dynon K factor as specified in the Dynon manual. Got it to the point where my fuel used (by Dynon) and fuel added (at the pump) were within .1 gallons. Pretty darn good, and was starting to feel confident in the Dynon readings.

Then - on my most recent trip, on climbout from Muskegon, MI, I got a high fuel flow alarm and a reading of over 10 GPH, up from the usual full throttle climb flow of 6.5 GPH. I leveled at cruise and the high reading continued. (I have the Dynon downloaded data file at the time of the incident.)I was clearly not really burning that much gas, as the engine continued to run fine and my actual consumption was normal for the leg. When I pulled the fuse for the electric boost pump, the flow returned to normal. This happened again on the next leg. Sudden onset, electric pump OFF back to normal, electric pump ON back to high rate. On my last leg all was normal.

I have yet to pull the top cowl and check the fuel pump for any signs of trouble - plan to do that tomorrow but would be surprised to see anything obvious. Is it possible the electric fuel pump is overpowering the engine driven pump and forcing extra fuel back through the return line? And why would this be happening intermittently? By any stretch of the imagination could this be a failure mode of the old style pump, and should I plan to replace it?

Any advice/theories appreciated.
  • Re: Intermittent high fuel flow indication

    by » 11 years ago


    John,

    Read SB 912-053UL from 2007 ...it includes this line:

    1.3) Reason
    Due to high fuel pressure, caused by exceeding pressure in front of the mechanical fuel pump (e.g. due to an electrical fuel pump), in limited cases a deviation in the fuel supply could occur. This can result in exceeding of the fuel pressure and might cause engine malfunction and/or massive fuel leakage.

    It required replacing the fuel pump with one that looked identical but of course a different part #. Now they have a completely new fuel pump that appears to be built for aviation. I would have to make the assumption that the SB didn't solve the original problem because that is exactly what mine does. I will be buying the new one.

    Pete

  • Re: Intermittent high fuel flow indication

    by » 11 years ago


    Your fuel flow sensor measures flow into the float bowls, not instantanious fuel used by the engine. My 912S frequently measures 8-9 GPH for short periods at high power. Converesly, sometimes it reads 0 GPH causing my heart to skip a beat. Slow down your Dynon scan time, if you can, and you will get a more even reading.

    Lary
    Rans S-7S

  • Re: Intermittent high fuel flow indication

    by » 11 years ago


    Hi John,

    Does it read like that if you only run on the mechanical pump?
    I have a Dynon D120 and it is fairly steady and has been for 740 hrs. I don't know how your is mounted, but could be a consideration. It could also be a poor wire connection since this just came out of the blue.

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


  • Re: Intermittent high fuel flow indication

    by » 11 years ago


    Hi,
    I have the 912 uls in a kitfox 5. It is setup with an electric backup fuel pump on the firewall, then the fuel flow sensor for my dynon d120 ,it then goes into the mechanical pump . I get high readings when I use the electic fuel pump (9usgal/hr) , ( on take off and landing), when I switch the electric off fuel flow is at the 4.8 USgal/hr. I am thinking if the fuel flow sensor was before the electric pump it would all be stable, but not sure.

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