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Thread: Engine Troubleshooting

  1. #1

    Engine Troubleshooting

    Hi there!

    As a first post here in EAA forums I have an interesting issue I'm working on.
    It's about a Lycoming IO-360-A1B6 in a Cardinal RG.

    It has a mag drop between 150 and 300 RPMs on the Right mag only. Left mag is 100.
    This also means it will not develop full power. The engine will run smooth, however, there's no sign of a cylinder not playing along.

    We have checked timing, swapped the spark plugs, ignition leads, magneto itself, ignition switch, to no avail. P leads were inspected and measured as well. Compression is good.
    The intake system looks fine, external visual inspection, and the injector nozzles were cleaned and inspected as well, all fine.

    Agressive leaning does not affect the drop as far as we could tell.

    Does anyone here have some experience with similar issues?

    Cheers!
    Last edited by NilsWright; 09-01-2020 at 02:50 AM.

  2. #2
    Update. We temporarily tried fine wire spark plugs, didn't help.
    We also tried to swap the top and bottom ignition leads T1 to B1 and vice versa. And then it was all good!
    Now this is very odd to us.

  3. #3
    robert l's Avatar
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    Quote Originally Posted by NilsWright View Post
    Update. We temporarily tried fine wire spark plugs, didn't help.
    We also tried to swap the top and bottom ignition leads T1 to B1 and vice versa. And then it was all good!
    Now this is very odd to us.
    So you're saying that switching the top plug wires to the bottom plugs, and the bottom plug wires to the top plugs fixed the problem?

  4. #4

    Join Date
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    A not very likely guess: there is a loose fit between the connector and the spark plug or the wire end and the connector and when you swapped them you got it tight enough. Try to wiggle it and see if its loose. See, told you its not a very good guess, but it would its one explanation. How's the fit with the other end of the wire at the mag? And a 150 drop might be within specs, and still the engine produce good power when running on both mags.

  5. #5

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    Bottom plugs are typically harder to fire than top plugs. Priming fuel and oil tends to foul them. If a resistance check on the bottom plugs shows low values, my guess is that one mag is firing a hotter spark. I will guess that looking at the internals of the mag that was originally firing the bottom plugs might find a wear issue.

    Best of luck,

    Wes

  6. #6
    Quote Originally Posted by robert l View Post
    So you're saying that switching the top plug wires to the bottom plugs, and the bottom plug wires to the top plugs fixed the problem?
    Yes. And this is what we went with in the end.
    Sent off mags just to be sure they were fine, but still had the issue. So we again tried swapping top and bottom leads, problem went away.

    Odd problem. And we dont fully understand how or why this happened. We'll keep a close eye on how it performs.

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