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Thread: Rough running engine when throttled back from full power at circuit height

  1. #1
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    Default Rough running engine when throttled back from full power at circuit height

    HI Folks - new Forum member / First Post / Visiting from Australia for 2 months

    I have a 2013 CC SS that I recently purchased. Just finished 2 weeks training at Tac Aero (which was great) but ran into a weird engine problem. Engine runs perfect on taxiing, warm-up, run-up and take off.

    Engine Roughness after throttle back
    However around the time we get to 1000ft and smoothly throttle back, we get noticeably rough engine running, rough enough to keep close to the rwy but NO engine shudder, NO miss and NO sign of quitting - more like a v bad mag check.

    Also the engine analyser data show that CYLs 1 and 2 run approx 100 degree cooler CHT than 3 and 4 during the rough running episode. The Savvy site is super cool - highly recommend.
    See graphs below

    Jon D, Don from CC's and Tac Aero has been super helpful. We think its Ignition related - unfortunately Klaus declined to spk with me (did send me the standard troubleshooting list on a Saturday) which as a customer is really disappointing.
    Jon D mentioned he had a customer in N/S Carolina that had near identical issue and it was the Mini-sensor.
    However we pulled the Mini-sensors and the internal solder all looked Ok - grrrhhh !!

    Actions
    So far we have
    1) replaced the coils with new - all 4 (initially we swapped the coils so each spark plug had a different coil - this didn't move the low temps from CYLs 1 and 2 as we hoped plus we still had the rough running at circuit height - so we DONT think its the coils - but just in case we have replaced them).
    2) replaced spark plugs, ALL Ignition leads
    3) replaced both the Mini-sensors with 2 new which is a bear of a job but Hayden from Tac Aero did a super job.

    Next is to install the intake spacer for the carby -while we are at it - for better fuel air mixture .

    Test flying the a/c tomorrow 15th May with these changes - so will send an update.
    If new Coils, new plugs, new ignition leads it only leaves one or both of the Ignition modules unless we are completely on the wrong track - which is always a possibility.

    So couple of questions
    1) Does this look like an Ignition system issue - problem effects 2 cylinders almost identically , only happens at throttle back after full power climb to circuit height
    2) Has anybody else had a similar issue as described , (the engine runs close to perfect at taxi, warm up and run up and climb out.)
    3) Is there any other suggestions to troubleshoot (checking main ignitions circuit breakers tomorrow. )
    4) What symptoms do failing coils normally exhibit
    5) What other possible issues could cause 2 CYLs to drop in temperature (CHT and EGT) like this.
    (We are assuming less or degraded spark to CYLs 1 and 2, less combustion, less heat causing rough running)


    Engine Monitor Graphs
    Green line is RPM

    First graph shows Abnormal engine performance (of which we now have several the same) shows CHTs 1 and 2 diverging sharply downward from CHTs 3 and 4 around the time we throttle back and see onset of noticeably rough running.

    Second graph is a normal engine performance - CHTs and EGTs move together up and down - as you would expect
    Even at 2450 PM - we see CYLs 3 and 4 CHT's of around 360/370 degrees but CYLs 1 and 2 are only 290/300 degrees




    The difference between the 2 is quite stark.

    Welcome all input and safe flying.

  2. #2
    Senior Member Dan L's Avatar
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    Default Re: Rough running engine when throttled back from full power at circuit height

    Two things come to mind right away. If the engine has over 500 hours change the spark plug leads. But youíve done that already.

    Second, have you leaned it aggressively when you throttle back?

    With full rich my O-340 will run rough under those conditions too. Even worse if I pull carb heat thinking it is ice. Leaning is all it takes for me.
    Flying Carbon Cub EX #11 since 2011

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    Default Re: Rough running engine when throttled back from full power at circuit height

    Quote Originally Posted by Dan L View Post
    Two things come to mind right away. If the engine has over 500 hours change the spark plug leads. But youíve done that already.

    Second, have you leaned it aggressively when you throttle back?

    With full rich my O-340 will run rough under those conditions too. Even worse if I pull carb heat thinking it is ice. Leaning is all it takes for me.
    +1 with Dan L. Also make sure your primer is properly seated and locked.

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    Senior Member chipallen's Avatar
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    Default Re: Rough running engine when throttled back from full power at circuit height

    I also use Savvy and have found them to be very helpful and professional. If you haven't found the problem by now, I suggest you send the data to them for analysis; my guess is you'll learn something that maybe you can use and share with the rest of us.
    Chip Allen
    SWT Aviation, Inc.
    Cubcrafters Southeast Sales Center
    Marietta, GA
    www.swtaviation.com

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    Default Re: Rough running engine when throttled back from full power at circuit height

    Quote Originally Posted by Dan L View Post
    Two things come to mind right away. If the engine has over 500 hours change the spark plug leads. But youíve done that already.

    Second, have you leaned it aggressively when you throttle back?

    With full rich my O-340 will run rough under those conditions too. Even worse if I pull carb heat thinking it is ice. Leaning is all it takes for me.
    Hi Dan

    We did lean the mixture during one of these episodes but it didnt make any difference.
    I was wondering would too rich a mixture cause only the front 2 CYLs (1 + 2) to run that much cooler.

  6. #6
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    Default Re: Rough running engine when throttled back from full power at circuit height

    Quote Originally Posted by chipallen View Post
    I also use Savvy and have found them to be very helpful and professional. If you haven't found the problem by now, I suggest you send the data to them for analysis; my guess is you'll learn something that maybe you can use and share with the rest of us.

    HI Chip

    Read many of your threads
    Savvy's response was

    "I merged your tickets into this one so all the flight data is in one place.
    The disparity between cyl 1-2 and 3-4 looks like a spark/ignition/timing issue.
    Idle MAP is low which argues against an induction leak.
    EGTs and CHTs for 3-4 don't drop when you reduce FF which argues against a fuel issue."

  7. #7
    Senior Member Springloaded's Avatar
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    Default Re: Rough running engine when throttled back from full power at circuit height

    Iím guessing it gets rough between 3/4-5/8 throttle as your bringing it back slowly. Itís probably not a consistent thing either. Iíve owned 4 2013 model CC all mine have seemed to have this little quirk some worse than others. Iím not telling you to do this but I have found that the mixture pulled out about 1/2-3/4Ē helps. I actually cut a hose and leave it on mine so mixture canít go in all the way. You probably have a avatar carb. They have a kit for the carbs that was in this year range but canít be used with avstar carbs. Mine seems to be worse when I do a max climb and pull the throttle back slow. Try just pulling it right back to 1/2 throttle see if it quits acting up. If you find the solution please share.
    Thanks
    chuck
    Chuck Kinberger
    Southern Cubs
    Florida Cubcrafter Sales
    Jupiter Fl.
    Pa11890ck@gmail.com
    You can sit at home & hear the News or get out there & be the News

  8. #8
    Senior Member Dan L's Avatar
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    Default Re: Rough running engine when throttled back from full power at circuit height

    I have the Avstar carburetor too. I donít take off with the engine leaned but it is quickly leaned once I get to my altitude. And like Chuck, I pull it back at least a half inch.

    Quote Originally Posted by Springloaded View Post
    Iím guessing it gets rough between 3/4-5/8 throttle as your bringing it back slowly. Itís probably not a consistent thing either. Iíve owned 4 2013 model CC all mine have seemed to have this little quirk some worse than others. Iím not telling you to do this but I have found that the mixture pulled out about 1/2-3/4Ē helps. I actually cut a hose and leave it on mine so mixture canít go in all the way. You probably have a avatar carb. They have a kit for the carbs that was in this year range but canít be used with avstar carbs. Mine seems to be worse when I do a max climb and pull the throttle back slow. Try just pulling it right back to 1/2 throttle see if it quits acting up. If you find the solution please share.
    Thanks
    chuck
    Flying Carbon Cub EX #11 since 2011

  9. #9
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    Default Re: Rough running engine when throttled back from full power at circuit height

    I second what chuck says, I experience this exact thing in my Ď13, so far my only alteranitve to it is pull the throttle back through this spot without hesitation and I donít notice it

  10. #10
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    Default Re: Rough running engine when throttled back from full power at circuit height

    Hi Folks,

    Just a quick note to advise we believe we have resolved this issue.

    Both symptoms (rough running and diverging cylinder temps 1 + 2 ) were NOT present on the test flight and engine operation was normal.
    WE replaced Spark Plug Leads, Coil and Mimi sensors plus some SBís / SAís
    Installed new intake plenum before new Coils/Leads mini sensors) Ė didnít fix the issue
    Intake spacer and vernitherm,installed same time as new coils/leads/mini-sensors.

    We believe replacing the Spark Plug Leads, 4 Coils and Mimi sensors has fixed the issue and this given my specific situation (14,000 miles from home and somewhat time limited) was the better option.
    Also it saved taking the cowl/cooling shroud and pulling the a/c to pieces a few times.
    A builder may well taken a different troubleshooting path.

    Logically we believe either the new Plug Leads or the new Mini Sensors resolved the problem, as swapping the coils didnít move the Cylinders with low temp.(But would welcome input)
    I will send the old Coils and Mini sensors to Klaus for checking Ė so there might be a definitive resolution.

    Aircraft ran very well in test flight and will get more hours on it asap.

    Thank to Klaus and Jon/Don for their inputs and advice Ė very valuable.

    Especially thanks to Hayden, Bryant and Erin from Tac Aero Maintenance who did a super job in getting all the new parts in the a/c.
    It was a very very big and difficult job getting the new Mini sensors installed and Hayden nailed it.

    Rgds Charles

    Engine Data from Successful Flight Ė No CHT divergence on CYLs 1 and 2

    [IMG]file:///C:/Users/Charles-PC/AppData/Local/Temp/msohtmlclip1/01/clip_image002.jpg[/IMG]
    [IMG]file:///C:/Users/Charles-PC/AppData/Local/Temp/msohtmlclip1/01/clip_image004.jpg[/IMG]
    Last edited by CharlesTym; 05-16-2019 at 11:15 AM.

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