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

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

    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
    One graph is a normal engine performance - CHTs and EGTs move together up and down - as you would expect

    Other graph 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.
    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


    Engine data - showing low CHTs - CYLs 1 and 2 after throttle back at circuit height.jpgNormal circuit - no rough running and normal CHTs EGTs.jpg

    The difference between the 2 is quite stark.

    Welcome all input and safe flying.

  2. #2
    Junior Member
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    Default Re: Rough running engine when throttled back from full power at circuit height - perf

    Check the plastic lines and plastic fittings that go from the MAP sensor to the lightspeed box behind the right kick panel. I found the plastic fitting behind the panel broken at the MAP sensor....mine was intermittent like yours after the fitting broke. Repaired mine with brass fittings and new lines....my bird is a 2010 SS. A customer had similar issues...his was broken at a t fitting by the lightspeed box

  3. #3
    Junior Member
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    Hood River
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    Default Re: Rough running engine when throttled back from full power at circuit height - perf

    Quote Originally Posted by Snoopy View Post
    Check the plastic lines and plastic fittings that go from the MAP sensor to the lightspeed box behind the right kick panel. I found the plastic fitting behind the panel broken at the MAP sensor....mine was intermittent like yours after the fitting broke. Repaired mine with brass fittings and new lines....my bird is a 2010 SS. A customer had similar issues...his was broken at a t fitting by the lightspeed box
    Thanks for the heads up. I saw the yellow plastic line to the MP gauge and wondered what would happen if there was an issue with the line. In this recent issue of rough running after throttling back the thing that lead us in the Ignition direction was the 2 cylinders with low CHT's. It would be good to get Klaus from Lightspeed to test the components we have taken off and replaced.

    Will get that done and keep every body update.

  4. #4
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    Hixson, TN
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    Default Re: Rough running engine when throttled back from full power at circuit height - perf

    Interesting problem! We had a similiar operation with a 2010 CC but we did not have CHT/EGT readings, just rough operation after pulling power back like you described. It turned out to be a carburetor gone bad. We knew this because once it started running rough we could pull the mixture more lean and make it smooth out again. Sent the carb in for a major overhaul and a tune on the carb flow machine and now it's perfect. I noticed your Cyl 1&2 EGTs going low on the 'normal' run which could be the beginning of the issue?? Keep us posted and best of luck.

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