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Following six months without use, and the 5-year rubber replacement, the engine driven fuel pump on my 912UL failed to operate in a ground test.  The pump was installed in 2015 and had about 200 hours on it.

Of concern is that the dead pump did not allow fuel to pass, either via gravity flow from the wing tanks of my Zenith 701, or the Facet electric pump. I demonstrated fuel flow to the inlet side of the engine mounted pump, but nothing at the outlet.

I thought that the engine-mounted pump was designed to allow fuel to pass through it on failure.  Is this correct?

I am simply replacing the errant pump,

  • Re: Dead 912UL Fuel Pump Pass Through

    by » 9 months ago


    I would look at it very closely.

    If the Inlet of the pump is clogged with debris, no fuel will pass.

    There is a filter built into the inlet.

    Were the New Hoses Flushed and Cleaned before they were installed?

    Just because they are New, does not mean they are clean!

    This would not be a fault of the pump.

     

    The pump is an inherently simple device.

    It is just a diagram and two flapper valves.

    If the Diagram ruptures, the pump leaks.

    If the Valves fail, they fail OPEN 99.999% of the time.

    The pump may quit pumping but doesn't block the flow.

     

    Before you just declare the pump as "Bad" and replace it, determine "WHY" it is bad.

    It might not be Bad at all.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


  • Re: Dead 912UL Fuel Pump Pass Through

    by » 9 months ago


    Well glad you found it on the ground. Odd timing as it’s time for a new mechanical pump anyway. Section 05-10 in the Line maintenance manual states they are to be replaced every five years just like the rubber. If you could open it up and find out what happened and post up what you found it would be much appreciated.  


  • Re: Dead 912UL Fuel Pump Pass Through

    by » 8 months ago


    Removed the faulty fuel pump and recycled the nipples onto the new fuel pump, which performed as advertised.

    Blew but mouth into inlet side of faulty fuel pump—clogged—would not pass air.

    Through hole for inlet nipple observed screen of faulty pump.  A translucent grey layer covered it.  My intention is to heat the pump body in order to try release the pump internals and better document the issue.  Happy to send the pump body to a more qualified individual.

     


  • Re: Dead 912UL Fuel Pump Pass Through

    by » 8 months ago


    Glad you found the problem.

    Did you pump a few ounces of fuel into a container to flush the fuel hoses before attaching the New Fuel Pump?

    Until the hoses are confirmed to be clean, the problem may re-occur in a short time.

    It would be prudent to identify the source and substance of the "Translucent Grey Layer".

    This might be indicative that something upstream is deteriorating.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


  • Re: Dead 912UL Fuel Pump Pass Through

    by » 8 months ago


    The Rotax Line manual states to check for “translucent, jelly-like contamination” when inspecting the carburetors but offers no further explanation or clarification.  Everything I can find  online about slime in fuel systems is regarding microbial growth in diesel or jet fuels.  If this were my plane I’d replace every fuel line and filter from the tanks forward and flush clean every mechanical component in the fuel system including the gascolator screen if you have one.
     


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