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Thread: fluctuating EGT

  1. #1
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    Default fluctuating EGT

    The last two flights my #1 EGT has been fluctuating. Has anyone seen this? How often are you changing the Denso plugs? Any ideas? 180 hours/FX3
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  2. #2
    Senior Member Andy's Avatar
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    Default Re: fluctuating EGT

    The fluctuating EGT readings are likely caused by an intermittent open circuit of the ground wire between the sensor and the GEA 24. (I had a similar problem with a CHT sensor on my new FX-3)

    You ask about plugs in the same post but I doubt spark plugs have anything to do with the EGT issue. I have not changed my plugs (FX-3 132 engine hours). Gaps were as new at first condition inspection.
    Last edited by Andy; 09-01-2021 at 08:14 AM.

  3. #3
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    Default Re: fluctuating EGT

    Agree, open circuit somewhere.

    In regards to plugs, a bad plug (or associated wiring) is easily identified on run up.

    For the CC340 on the EX-2, manual states to inspect and clean the plugs every 100hrs. I just replace the plugs every 100hrs because they are cheap (Sparkplugs.com, Rock Auto, ....).
    Dan Arnold
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    Default Re: fluctuating EGT

    Quote Originally Posted by aeroaddict View Post
    Agree, open circuit somewhere.

    In regards to plugs, a bad plug (or associated wiring) is easily identified on run up.

    For the CC340 on the EX-2, manual states to inspect and clean the plugs every 100hrs. I just replace the plugs every 100hrs because they are cheap (Sparkplugs.com, Rock Auto, ....).

    There is no loose wiring that I could find. I tested the resistance of the plugs. Plug from top of cylinder #1 was 6 times the normal readings of the other 7 plugs. The runup was normal, so this bad plug was not easily identifiable. I've ordered a new set. I expect that will fix the problem.

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    Default Re: fluctuating EGT

    Quote Originally Posted by KCKS View Post
    There is no loose wiring that I could find. I tested the resistance of the plugs. Plug from top of cylinder #1 was 6 times the normal readings of the other 7 plugs. The runup was normal, so this bad plug was not easily identifiable. I've ordered a new set. I expect that will fix the problem.

    This was a very instructive problem. The high power run-up showed no RPM change when switching between 1 and 2. However, the fluctuating EGT temperatures did indicate a problem. I put in new plugs and problem solved.

  6. #6
    Senior Member Andy's Avatar
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    Default Re: fluctuating EGT

    Quote Originally Posted by KCKS View Post
    This was a very instructive problem. The high power run-up showed no RPM change when switching between 1 and 2. However, the fluctuating EGT temperatures did indicate a problem. I put in new plugs and problem solved.
    Thanks for the report. I had not realized that a misfiring plug would raise the EGT but here is an extract from a Savvy Analysis report that I received in my email today:

    “If one of the #2 spark plugs had stopped firing, we would expect to see EGT #2 rise by about 50°F to 100°F and CHT #2 start to decline a bit."



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    Default Re: fluctuating EGT

    Interesting, can't say that is intuitive from my brain on the EGT's. CHT's yes.
    Dan Arnold
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    Default Re: fluctuating EGT

    Quote Originally Posted by aeroaddict View Post
    Interesting, can't say that is intuitive from my brain on the EGT's. CHT's yes.
    It has to do with the flame front and time. Think of it this way, if you and your buddy were on opposite ends of a field and both lit the field on fire, it would take ~half the time to burn all the way across as compared to if you were trying to light the field afire all alone. Two mags is lighting the fuel air mixture (the field) on fire from both, opposite sides.

    Inside the cylinder operating with one mag, the fuel air mixture takes more time to burn and, as such, it is still burning or was just burning as the exhaust valve opens. The exhaust going past the temperature probe is hotter and you get the higher EGT.

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    Default Re: fluctuating EGT

    Got it!

    Cheers,
    Dan
    Dan Arnold
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  10. #10
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    Default Re: fluctuating EGT

    Quote Originally Posted by Andy View Post
    Thanks for the report. I had not realized that a misfiring plug would raise the EGT but here is an extract from a Savvy Analysis report that I received in my email today:

    “If one of the #2 spark plugs had stopped firing, we would expect to see EGT #2 rise by about 50°F to 100°F and CHT #2 start to decline a bit."



    So Andy gave me a chance to plug Savvy analysis. It's a great service, relatively inexpensive and they are excellent diagnosticians. I just use the EGT analysis, but they just added FX3 to their full maintenance service. They are the ones that figured out my problem

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