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Sudden fuel pressure drop

in 912 / 914 Technical Questions 13 years ago

  • Re: Sudden fuel pressure drop

    by » 13 years ago


    Roger, I do use 91 octane. The sender is horizontal on the firewall. I drilled a hole through the firewall and the sender is on the cabin side with the hose fitting protruding into the engine compartment. See attached photo taken during early construction (the wiring looks a lot better now).
    DSC03127.JPG (You do not have access to download this file.)
      
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  • Re: Sudden fuel pressure drop

    by » 13 years ago

    Hi Paul,

    Well my solution may or may not be your answer. I was not expecting horizontal, but it may have enough downslope on the hose to cause the same problem. About 4 years ago I remote mounted my fuel pressure sender on my firewall and I had it hang upside down with about 18" of hose. After a year of using 91 oct. my low fuel pressure alarm kept going off. My normal fuel pressure was 3.8psi, but then during take off some times my fuel pressure reading would drop to 1.2 psi and the alarm went off. This was about 40%-50% of the time over 3 weeks. I always tell people fly the plane and not any one instrument. I thought it might be a bad sender so I pulled the sender off the bottom of the hose and all this oily smelly liquid came out. Smelled like turpentine. Then I knew exactly what it was. The 91 oct. sat in that hose and it never got changed out by hanging upside down. It cooked and cooked until the fuel was trash in the hose. So I took the sender and used carb cleaner in a spray can with a little red plastic nozzle and held it up into the small orifice of the sender. I gave it a quick shot directly into the sender's orifice 5-6 times and let it pee out. Then I opened my fuel valve and let some fresh fuel drain out the bottom of the hose. After I put it back together I never had another problem for another year or so. I have now seen dozens of these just like mine with the same problem. During any of my clients inspections I now pull the sender and clean the sender and hose. Since I have done that none of them have had any issues with low fuel pressure readings. I have since then mounted my fuel pressure sender above the engine so after shut down and while it sits in the hanger the fuel in the line bleeds back down out of the hose and away from the sender. Then on start up it always gets fresh fuel. That was 3 years ago and I still have the same sender and it is rock solid still at 3.5 psi and never any more low fuel pressure alarms.

    Now yours isn't hanging down, but maybe the hose has enough of a downward slant to keep all the old fuel in the hose and it never gets replaced or freshened up.

    I do not know if this is your problem, but certainly something you may want to rule out. 100LL does not have this issue with the degrading of the fuel with heat and time.


    Just food for thought and a cheap and easy check.

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

    Thank you said by: Paul Owen
      
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  • Re: Sudden fuel pressure drop

    by » 13 years ago

    Do you have a Dynon D120 or other EMS? Does this sit on top of your engine covered with a piece of fire sleeve? What is it? It's an antenna and transmitter so Uncle Sam can keep an eye on you. Okay maybe not. :unsure:
    What it really is is a fuel pressure pulsation dampener. It should be mounted in line after the out side of the fuel pump and it helps keep the pulsation coming out of the pump from reading on your fuel pressure gauge.
    5543.jpg (You do not have access to download this file.)

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

      
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  • Re: Sudden fuel pressure drop

    by » 13 years ago

    That actually makes a lot of sense for my situation. The sender does sit considerably lower than its fuel supply, and I know the same fuel just sits and sits in it. I'd just never realized that could cause such a problem. I'll clean it out this week and I'll let you know what happens. Thank you so much for your time and thought.
      
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  • Re: Sudden fuel pressure drop

    by » 13 years ago

    I have a Grand Rapids EIS, and I don't have a dampener. Maybe I should get one.
      
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