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912 ULS running rich

in 912 / 914 Technical Questions 7 years ago
My 912 ULS is running very rich. The fuel pressure at the mechanical pump is fluctuating and goes off the scale.
I confirmed that the pressure relief orifice is open and fuel is going back through it to the fuel tank.
This is a new pump, installed recently. The engine ran fine for a few hours after installing the pump.

Any ideas?

Thanks,
Claude

  • Re: 912 ULS running rich

    by » 7 years ago

    Why do you think it's running rich? Just because of the fuel pressure indication?
    What is your fuel pressure gauge alarm set at? The old pressure was 5.8 psi and the new is 7.2 psi. This could be a bad sender. It is one of the more common reasons for erroneous readings.
    If you have air in the system it will fluctuate until that clears. Air is compressible and the liquid fuel isn't.
    I had the same problem once. Looked everywhere for a loose or bad wire. I knew it wasn't a real pressure. I found the problem at the fuel pressure sender. Even though the spade connectors felt tight I finally squeezed them even tighter with a pair of pliers and the problem went away.

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

      
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  • Re: 912 ULS running rich

    by » 7 years ago

    Actually we are measuring the pressure with a mechanical fuel pressure gauge which we hooked up to the line after the pump.
    The pressure is going off the scale which tops at 9 psi on this gauge.

    Claude
      
    Report

  • Re: 912 ULS running rich

    by » 7 years ago

    Also, spark plugs are black and seem to be worst on the left side.
    The engine sometimes runs very rough.

    Claude
      
    Report

  • Re: 912 ULS running rich

    by » 7 years ago

    It is possible to have a bad pump. Anyone around you you can swap pumps with for a run? If you are getting 9 psi right after the pump and it is confirmed on two gauges I think I would trade that pump in.

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

    Thank you said by: Awod Alahmari
      
    Report

  • Re: 912 ULS running rich

    by » 7 years ago

    Thanks Roger, I will give that a try.

    Claude
      
    Report
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