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Thread: Lycoming 0320 intermittent power loss

  1. #1

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    Default Lycoming 0320 intermittent power loss

    My CFI has a 160hp lycoming 0320 in a PA22/20 that he is pulling his hair out over. Intermittently it has a power loss in flight. Starts loping and missing, scares the crap out of everyone, then it comes around. Never does it on the ground, only at various points in the traffic pattern. Sounded like a fuel problem so we did some testing. Did it on Mogas and 100ll. Did it either tank. Gascolator clean, if we disconnect the fuel line there and open the fuel valve we get approximately 60 GPH running out (5 gallons in 5 min). Replace line from gascolator to carb still did it. A friend of his told him about a Lycoming SB that states a problem with turbulence caused by the diameter of the bore in the sump and the carb diameter being different. He changed both. Still did it. Of course this SOB plane will never act up on the ground, so troubleshooting it has been quite the joy! The plane has no CHT, no EGT, basically no engine instrumentation other than the tach.

    This plane has 45 hours SMOH. New cylinders etc. Carbon buildup is highly unlikely

    So we are left with some bizarre fuel problem or we are starting to think that its an intermittently sticking valve. Today we got an oil filled vacuum and flew hoping it would act up and we could start moving towards fuel or mechanical issues. Of course it did not act up. However I have been doing some reading and some people mention poor cylinder cooling causing localized hotspots and causing a valve to stick. So after our flight today we took some thermal images. One of these jugs is significantly hotter than the rest.Or one is way cooler. More testing to come. We are either seeing a hot jug or a cold one....

    Baffling? Anyone seen heat cause intermittent valve sticking? Any suggestions for nailing this problem down?

    Once we get it to act up in flight with a vacuum gauge on it then we will know for certain its a mechanical issue, but this just doesnt look right to me!

    FLIR0086.jpgFLIR0080.jpg

  2. #2
    Brian's Avatar
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    Default Re: Lycoming 0320 intermittent power loss

    How about the Magnetos? Slicks or Bendix? Rebuilt or replaced with the recent engine overhaul? My experience with exhaust valve sticking at high power settings results in such violent shaking that you immediately pull the throttle back to keep the engine from departing the airframe. Magneto failure usually less dramatic but still can still present significent power loss and or misfiring depending on whats failing within the mag.
    Brian
    Monrovia, CA

  3. #3

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    Default Re: Lycoming 0320 intermittent power loss

    It seems so abrupt that the mags haven't really been suspect. Both at once? I haven't been in the airplane when it does it, but it sounds like more of a complete loss of power (ie fuel) than missing. We need it to act up with a vacuum gauge hooked up and for anyone ever wanting to test it you need this oil filled gauge....

    https://www.amazon.com/dp/B00G008X1M..._L5lKBbTS7A3Z8

    I will post the findings as we move forward

  4. #4
    Brian's Avatar
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    Default Re: Lycoming 0320 intermittent power loss

    Complete loss of power indeed sounds more like fuel starvation for sure. I thought you were more describing a rough running engine. Exhaust valve sticking on the other hand will not feel like fuel starvation but more like the engine is coming apart. A blocked exhaust due to muffler flame tube coming apart has been reported to cause signifcant power loss but pretty unlickly to be so intermitent in nature.
    Brian
    Monrovia, CA

  5. #5
    Administrator Steve Pierce's Avatar
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    Default Re: Lycoming 0320 intermittent power loss

    Have seen mag switches ground out intermittently.

  6. #6
    Gilbert Pierce's Avatar
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    Default Re: Lycoming 0320 intermittent power loss

    Disconnect the P leads and go fly.

  7. #7

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    Default Re: Lycoming 0320 intermittent power loss

    It is a long shot, especially if the mags are new, but I have seen several Bendix coils go bad, and it is quite common for them to not fire while hot, then after cooling off begin working fine again. Of course, while flying they don't both begin misfiring at the same time, however when the first one begins misfiring it is very subtle, and not until the second one begins misfiring does it become VERY evident. Assuming the coils were not replaced at overhaul, it is possible one of the coils have been acting up for years without being detected, and only since the second one has begun acting up does the the problem show itself.

    I have for years gotten in the habit of doing a 'mag check' near the end of each flight - mostly just checking for fouled plugs, but once I had a coil fail during the flight - REALLY gets your attention when you select that mag! (until that point, I had no clue that anything was wrong)

    This is a great time to justify an "investment" in a CHT/EGT gauge for all cylinders. (I've got 1,000 ways to spend your money)

  8. #8
    Administrator Steve Pierce's Avatar
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    Default Re: Lycoming 0320 intermittent power loss

    Look up the tailpipe as well and verify the flame tube is intact.

  9. #9

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    Default Re: Lycoming 0320 intermittent power loss

    internal muffler as suggested in the previous notes does happen intermittently..... I'd sure look that over really well. Get a camera up into the tail pipe and exhaust system if you can.
    Tom Ferraro
    PA22/20-160 N25TJ

  10. #10

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    Default Re: Lycoming 0320 intermittent power loss

    One thing that is definitely not a culprit, still haven't gotten it to act up with a vacuum gauge on it.

    IMG_20180907_162916.jpg

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