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Thread: A question on leaning with my 3400 EM

  1. #11
    The number is the number of degrees from peak (i.e. 12L is 12 degrees Lean of peak).

    When the cylinder peaks the fuel flow is recorded and then checked against to determine rich or lean. It is assumed that leaning the engine will result in a lower fuel flow so if the current fuel flow is less than it was when the cylinder peaked the display will show 'L' for lean. If the current fuel flow is greater than the peak flow then the display will show 'R' for rich.

    I believe it is possible to have what Don was seeing on a carbureted engine, especially, if the bowl was near empty when the cylinder peaked. The act of the bowl refilling could result in an increase in fuel flow that would be interpreted by the peak detect mechanism as a turn in on the mixture valve. Because of the natural fluctuations in fuel flow with carbureted engines users should be aware that momentary jumps in fuel flow may be observed. The delta temperature display will still be accurate regardless of fuel delivery type (i.e. carbureted or fuel injected).

  2. #12
    chardks,
    My Lycoming engine is equipped with a Bendix fuel injected system. Could the issue I was referring to at the beginning of this thread, be caused by a problem with a fuel injected system.
    Don

  3. #13
    Quote Originally Posted by chardks View Post
    The number is the number of degrees from peak (i.e. 12L is 12 degrees Lean of peak).

    When the cylinder peaks the fuel flow is recorded and then checked against to determine rich or lean. It is assumed that leaning the engine will result in a lower fuel flow so if the current fuel flow is less than it was when the cylinder peaked the display will show 'L' for lean. If the current fuel flow is greater than the peak flow then the display will show 'R' for rich.

    I believe it is possible to have what Don was seeing on a carbureted engine, especially, if the bowl was near empty when the cylinder peaked. The act of the bowl refilling could result in an increase in fuel flow that would be interpreted by the peak detect mechanism as a turn in on the mixture valve. Because of the natural fluctuations in fuel flow with carbureted engines users should be aware that momentary jumps in fuel flow may be observed. The delta temperature display will still be accurate regardless of fuel delivery type (i.e. carbureted or fuel injected).
    Hi Thanks for that now it all makes perfect sense

  4. #14
    The number is the degrees from peak and rich or lean.
    Rob Hickman
    Advanced Flight Systems Inc.

  5. #15
    Quote Originally Posted by Don Patterson View Post
    chardks,
    My Lycoming engine is equipped with a Bendix fuel injected system. Could the issue I was referring to at the beginning of this thread, be caused by a problem with a fuel injected system.
    Don
    Don,
    I sincerely doubt this is a 'problem' with the fuel injection system. Perhaps the location of your fuel flow transducer has something to do with it. We have found the best place for the transducer is between the fuel injection servo and the distribution spyder. This location is least susceptible to pulses in the fuel line that can lead to fluctuations in the fuel flow.

    I would just recommend that when leaning your engine keep an eye on the fuel flow. If it jumps around a little you will just need to put less stock in the 'R'/'L' indications displayed by the efis.

  6. #16
    Chardks,
    My fuel flow servo is mounted mid point between the Bendix fuel injection servo
    and the distribution spider as you recommended. However it's mounted to a bracket
    that is then held in place by bolts holding on the sump. Maybe some
    vibration could be my cause. Thanks for your input and I will keep an eye
    on fuel flow when leaning.
    Any possibility this could be a sign that the engine driven fuel pump is ready
    to give some problems?
    Thanks again for your help.

  7. #17
    Don, I cannot speculate about the longevity of your fuel pump. Please leave that to someone more qualified than me. Thanks.

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