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Intermittent Low Fuel Pressure

in 912 / 914 Technical Questions 6 years ago

  • Re: Intermittent Low Fuel Pressure

    by » 6 years ago

    What plane is this? Do you have an electric pump? Did you install the restrictor or did it come from the factory already to go? If it has a spec faucet electric pump at 3.5 gpm they are learning this may not be enough and you could go to the next larger size. Plumbing too may have an influence on pressure and the obstruction could be any where. Could even be in a check valve if you have one.

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

      
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  • Re: Intermittent Low Fuel Pressure

    by » 6 years ago

    This is a Kitfox SS7, with high wing fuel tanks, gravity flow, and no electric fuel pump-pretty common for Kitfox. The 912uls was purchased new in 2013 and I purchased the return restrictor/fitting from Lockwood and installed it, and yes the restrictor jet size has been checked and is the correct size. Fuel flow tests have been done at the carburetors and just before the mechanical fuel pump, always indicate OK. A mechanical pressure gauge has been installed to check the digital readout and they both agree even during the intermittent low pressure. As you can see, I have been fooling with this issue for years and finally quit worrying about it because it never affects the engine power even for an instant. I have quite a trail of forum postings on this issue several years ago if you care to search back.
      
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  • Re: Intermittent Low Fuel Pressure

    by » 6 years ago

    Have you replaced your engine driven fuel pump with the new style pump? There was a SB or somesuch on this years ago... I replaced mine but it didn't fix the low fuel pressure issue. But my problem was vapor locking, caused by the blocked return line. Sounds like yours is something else.

    The Vans RV-12 fuel system is similar to mine and a lot of other low-wing Rotax powered airplanes. However, Vans wires the "aux pump" direct to the master switch so it is on all the time. I suspect (!) they did this to combat the common low fuel pressure complaints that many similar airplanes have. Does turning on your aux pump bring the fuel pressure back up?

    The POH for my airplane specifically says NOT to use the aux pump for takeoff and landings.... how this plays out with the RV-12 setup is not clear.
      
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  • Re: Intermittent Low Fuel Pressure

    by » 6 years ago

    The plot thickens. I hadn't heard of any high-wing aircraft having this problem. I agree, I never had any engine performance issues when the low fuel pressure light was on. I tried to get a spec on fuel pressure requirements for the Bing carbs but wasn't successful. But our experience would indicate it's a non-problem although I found it worrisome.

    Are your fuel caps in good shape? My buddy had a leaking fuel cap on his Flight Design CT.... the slipstream sucked all the fuel out of that tank while he was flying over the Grand Canyon.... he didn't say anything about low fuel pressure though. Might be something to check anyway.
      
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  • Re: Intermittent Low Fuel Pressure

    by » 6 years ago

    Barrie, my engine has the new style fuel pump, and yes I have checked the fuel tank cap gaskets. In fact some time ago I replaced them with the high quality Mercedes Benz gaskets that many people recommended.
      
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