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Problems with the low full pump pressure

in 912 / 914 Technical Questions 12 years ago

  • Re: Problems with the low full pump pressure

    by » 12 years ago

    Many thanks for the quick response
    In the pilots operating handbook (Sting s4 -Tl ultraligt)there is a warning that operating of both the engin driven and the auxiliary fuel pump for take and landing is not recommended, the combind pump output has been observed to ovrercome the carburetor float valve fuel cutoff etc....cause engin failure, Can i in mean time, to be on the safe side to Use the two pumps while cursing till the problem is solved
    A lot of plans that have Rotax engine do it as a must

    .


    ruv k,
    I have the exact same plane that I took delivery of in January 2012 and had the exact same problem, except my low pressure reading were even lower (0.9 psi) and I was getting high pressure alerts also. I also have the Skyview system (dual 10" screens). I struggled with this for many months. I got a new fuel pump installed at 25 hours and it seemed good for a few hours but then started up with the low and high pressure warnings. I always used the aux pump on the low warnings until it normalized. The aux pump immediately restored pressure readings but if I turned it off they would sometimes revert to the low readings, so I would leave it on for a while at times. The engine would never studder so I suspected that the sender was the problem.

    Anyway here's the solution I came up with and I highly recommend it. I purchased the Kavlico 0-15 psi pressure sensor from Dynon ($95 plus shipping). I had my 100 hour engine service done and had the Kavlico installed in place of the VDO unit. What I found out was that the fuel pump was putting out 7 psi at 3500 rpm's on testing of the Kavlico. We shut the engine down and checked the drip trays and sure enough there was fresh fuel there, so the 7 psi seemed correct. They changed out the mechanical fuel pump and it now reads between 3.5 to 4.5 psi during cruise. When I pull the throttle to land it has gone up over 5.6 psi but only at idle throttle settings and not all the time. It has never gone over 6 psi. I have 10.5 hours on this new sender and so far I couldn't be happier. The mechanic mounted the Kavlico on the firewall up high with the fuel line feeding from the bottom.

    The only issue on the installation is that it requires a 5 volt source (there are 3 wires on the sender), so we took this off of pin 18 (you need to check this) of the EMS module. This pin is normally for manifold pressure and I don't use that gauge.

    Hope this helps.
    Thank you said by:
      
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  • Re: Problems with the low full pump pressure

    by » 12 years ago

    I must finish the story about the low fuel pressure, I did what the forum moderator recommended to check the full pressure with a along pressure gauge( At the fuel line )and we found that the pressure was O.K .During the test we found that the return line from fuel junctionto gascolator was blocked , it was clear that this line should be open, or it might cause vapor lock and lose of fuel pressure ,we fixed it
    we thought we solved the problem, but ..... after several hours of flight the low pressure returned to its low pressure. we replaced the fuel pressure transmitter, and since then I have flown 10 hour
    with no problems white the low pressure and it is between: 3.5 to 4.5 psi
    But……in the last flight at the short final at 2500 rpm I got a height pressure warning for short time
    To be continue....
      
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  • Re: Problems with the low full pump pressure

    by » 12 years ago

    Hi, on the Dynon D120 , I know different but similiar.

    The 5 volts "excitation" power wire for the sensor can be a shared source.

    The other two wires off the sensor would be a ground and a display function.

    The ground should be hooked to a ground pin ( shared or not) that goes directly to the ems plug

    The display wire would need to go into the ems plug, in the spot designated for the fuel pressure.

    hope this is helpfull
      
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  • Re: Problems with the low full pump pressure

    by » 12 years ago

    Apologize for the late response is the Kavlico 0-15 psi pressure sensor you purchased from Dynon replaced the transmitter ,(the fuel pressure sending unit as shown in this link)

    www.egauges.com/vdo_send.asp?Sender=30PSI
      
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