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Thread: Ignition Problems. Help??

  1. #11
    Senior Member Andy's Avatar
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    Default Re: Ignition Problems. Help??

    Quote Originally Posted by J12345T View Post
    Sometimes when you start it up it runs beautifully and the next time you start it it displays the roughness on the R side. By roughness I mean; the front two cylinders are either not firing or mistiming badly. There are even backfires.
    Did the timing strobe test provide any useful information?

  2. #12
    Senior Member Dan L's Avatar
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    Default Re: Ignition Problems. Help??

    I wonder if it could be in your key switch? Or a bad breaker from the battery?
    Flying Carbon Cub EX #11 since 2011

  3. #13
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    Default Re: Ignition Problems. Help??

    Hi All,

    Update; swapped the ignition boxes left for right and the problem remains on the R side. So not the boxes.

    Definitely the front two cylinders are running cold in the failed condition.

    Have swapped coil and no change so not the coil. Likewise run external wiring so not a coil wiring issue. Will look to change ignition leads as a matter of course though.

    Pulled the R side 'input' plug apart to check. Looks okay.

    Checked sensor installation and gapping. All okay.

    Other interesting thing is that the EI RPM gauge shows ~50% of actual rpm when the unit is faulting. More interestingly is that this happens sometimes when running on Both indicating a fail condition being masked by the operating L side...

    Speaking with Klaus he says this points to the lower sensor pair..

    Quote Originally Posted by Andy View Post
    Did the timing strobe test provide any useful information?
    Andy. Haven't done that test as it is not always in a failed condition. We're going to rig up something similar having narrowed things down to (probably) the lower sensor pair.

    Regarding the ignition switch; yes pulled apart and checked. Like new.
    If it was a breaker issue (or power issue) then all cylinders would not work on R side unit.

    A very frustrating problem.

    Cheers,

    James
    Last edited by J12345T; 02-18-2021 at 06:45 PM.

  4. #14
    Senior Member Andy's Avatar
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    Default Re: Ignition Problems. Help??

    Quote Originally Posted by J12345T View Post
    A very frustrating problem.
    I'm sure, but thanks for sharing. Trying to understand your problem has made me study the ignition system schematics and the ignition system manual in more depth than I had before. I think the symptoms you have documented are consistent with an intermittent failure of the channel B input from the bottom crank sensor.

    (Bottom crank sensor feeds only the right ignition module. Right ignition module drives bottom plugs only. Channel A of the right module drives cylinders 3 and 4. Channel B of the right module drives cylinders 1 and 2. Tachometer output is only present is there is a sensor input so it's reasonable to assume tach output is halved if half the sensor input pulses are lost)

  5. #15
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    Default Re: Ignition Problems. Help??

    Quote Originally Posted by Andy View Post
    I'm sure, but thanks for sharing. Trying to understand your problem has made me study the ignition system schematics and the ignition system manual in more depth than I had before. I think the symptoms you have documented are consistent with an intermittent failure of the channel B input from the bottom crank sensor.

    (Bottom crank sensor feeds only the right ignition module. Right ignition module drives bottom plugs only. Channel A of the right module drives cylinders 3 and 4. Channel B of the right module drives cylinders 1 and 2. Tachometer output is only present is there is a sensor input so it's reasonable to assume tach output is halved if half the sensor input pulses are lost)
    Thanks Andy,

    That's exactly the conclusion we've come to as well.

    I'm thinking the easiest way to test it will be to put an appropriate voltage through the correct pins then pass a magnet over the sensor. By rights a voltmeter (on the correct pins) should show a closed circuit; and we can test each channel individually. Do you know by any chance what an appropriate voltage might be? I'm guessing 12v or maybe we just test for continuity?

    Regardless, I think we'll be removing the lower sensor and sending it in for testing/ replacement; well out of warranty though..

    Cheers,

    James.

  6. #16
    Senior Member Andy's Avatar
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    Default Re: Ignition Problems. Help??

    Quote Originally Posted by J12345T View Post
    That's exactly the conclusion we've come to as well.
    The only problem with that conclusion is that it requires the A and B channels of each system to be completely independent. I would have expected either the A, or the B, sensor channel to drive both output channels if one of those sensor input channels failed. (Channel A sensor would drive Channel B output and keep cylinder 1 and 2 bottom plugs alive)

    I have emailed Klaus to ask whether the A and B channels are completely independent in each module.

    I don't know your experience with electronics or your access to test equipment. If I had your problem I'd put a temporary breakout between the input harness and the ignition module input connector. I'd use that temporary breakout to feed sensor channels A and B to a digital storage oscilloscope and use that to capture the sensor input waveforms for normal and abnormal operation.

    A static test may show the problem but testing with the engine running and being able to capture the waveforms would probably be more informative.
    Last edited by Andy; 02-19-2021 at 01:16 PM.

  7. #17
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    Default Re: Ignition Problems. Help??

    Quote Originally Posted by Andy View Post
    I don't know your experience with electronics or your access to test equipment. If I had your problem I'd put a temporary breakout between the input harness and the ignition module input connector. I'd use that temporary breakout to feed sensor channels A and B to a digital storage oscilloscope and use that to capture the sensor input waveforms for normal and abnormal operation.
    Unfortunately I'm just a layperson trying to help the engineers fault find etc. We could get avionics involved again but I'd have to weigh all the mounting costs up against just replacing the sensor.

    Update; I've just checked the price of a new sensor!! Yikes although maybe that price (USD ~3000) is for the entire system??

    Cheers,

    James.
    Last edited by J12345T; 02-19-2021 at 02:46 PM.

  8. #18
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    Default Re: Ignition Problems. Help??

    Quote Originally Posted by J12345T View Post
    Unfortunately I'm just a layperson trying to help the engineers fault find etc. We could get avionics involved again but I'd have to weigh all the mounting costs up against just replacing the sensor.

    Update; I've just checked the price of a new sensor!! Yikes although maybe that price (USD ~3000) is for the entire system??

    Cheers,

    James.
    switch them.

  9. #19
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    Default Re: Ignition Problems. Help??

    Here is the last paragraph in my post about it:

    http://forum.cubcrafters.com/showthr...ll=1#post23176

    Another test of the system once you have the engine installed (prop can be on or off)......either remove all the spark plugs (especially if no prop on and you want to turn the engine over by hand using the flywheel) or remove the spark plug wires from the spark plugs. Also remove the spark plug wires from the coils. With the master switch ON and the ignition switch on BOTH, turn the flywheel around quickly and you should see the 4 coils “snap” or fire/spark each time the flywheel magnets pass the sensors. All 4 should work.

    That price you got is for the entire system, not the mini-sensor.

    Quote Originally Posted by J12345T View Post
    Unfortunately I'm just a layperson trying to help the engineers fault find etc. We could get avionics involved again but I'd have to weigh all the mounting costs up against just replacing the sensor.

    Update; I've just checked the price of a new sensor!! Yikes although maybe that price (USD ~3000) is for the entire system??

    Cheers,

    James.
    Dave Embry
    "You only live once.......but if you do it right.........once is enough."..

  10. #20
    Senior Member Andy's Avatar
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    Default Re: Ignition Problems. Help??

    Quote Originally Posted by Andy View Post
    I have emailed Klaus to ask whether the A and B channels are completely independent in each module.

    Klaus replied that the A and B channels are independent because they need to fire 180 degrees out of phase with each other.

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