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Fuel Pressure alarm

in General Tech Discussion 10 years ago

  • Re: Fuel Pressure alarm

    by » 10 years ago

    You still need to put a mechanical gauge inline to look. Even though your instrument is correct you need to rule out the pump, sender or other obstructions in line. This is just one diagnostic tool to look for your problem.At this point you have only ruled out the instrument not anything in the rest of the system.

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

      
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  • Re: Fuel Pressure alarm

    by » 10 years ago

    You are right Roger, as usual, I have ruled out the electronic pressure sensor, but not the Dynon readout on the screen that converts voltage signal to psi. I have also ruled out obstructions in the line thru careful inspection of all lines and orifice sizes. Of course the pump itself will be the last thing to rule out.

    There is one more thing I am going to try, and that is to disconnect my carb vent lines from the back of the air filters and let them hang free. I got to thinking about this and realized that with them connected to the air filters the intake manifold vacuum is applied to the carb float bowls, which may allow the needles to lift off their seats at a lower pump pressure, especially at WOT. However, I don't see that there is any difference between this and the Rotax airbox with the vent lines connected to the airbox.
      
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  • Re: Fuel Pressure alarm

    by » 9 years ago

    OK Roger I have ruled everything out except the fuel pump itself:

    - I connected a mechanical gauge so I could read both at the same time and found my electronic panel gauge and mech gauge tracked each other perfectly. The low pressure readings during WOT climbout showed up also on the mech gauge (as low as 1.6 psi), but only temporarily for about 30 seconds or so. Then the pressure would climb back to 2.5 or so while still at WOT climb.

    - I tried disconnecting my carb vent tubes from the back of the air filters and let them hang per stock instructions-made no difference.

    - I do have a fuel bypass recirc system per Rotax instructions. I also have a damping orifice in the fuel gauge line-made no difference with or without this orifice.

    - My fuel pump drain tube exits low inside the cowl-not in a hi pressure area.

    - All fuel and gauge hoses (except from tee to carbs) are firesleeved.

    - I have check the lines for obstructions and found none; this is also proven by the fact that the pressure does climb back within normal limits after a short period of time.

    As I said before, the engine runs fine thru all of this without a hiccup for 150 hours now. I am at my wits end now and don't know what else to check. It continues to nag at me and upsets my passengers when the low pressure alarm comes on (set at 2.1 psi).

    Should I make a warrenty claim on the fuel pump? Will Rotax require me to send in the old one for evaluation before sending out a replacement? I don't want to be unable to fly for that long.
    What would you do?

    Jim
      
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  • Re: Fuel Pressure alarm

    by » 9 years ago

    Hi James,

    Is there another Rotax engine close by that you might be able to borrow their fuel pump for a test run?

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

      
    Report

  • Re: Fuel Pressure alarm

    by » 9 years ago

    The other Rotaxes close by are all having the same issues as mine, so I wouldn't trust trying their fuel pumps.
      
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