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I just finished replacing all the spark plug wires and caps and also fixed a cracked power wire to one of the SMD's.  Anyway, engine didn't fire.  I stopped for the day as it was getting late.

When I ohm'ed the ignition coils though, I am getting 16.2K Ohms.  The manual says 6.1k.  Any ideas?

To test the high side, I put one test probe in the #1 Top spark plug cap and then the #2 Top.  #3 Top to #4 Top, etc.  Am I maybe testing this incorrectly?  Wondering if maybe the caps add to the resistance.

Anyway, I'm guessing I may have wired something incorrectly when I put the SMD's back together.  Is it safe to just start by hooking up just one of the SMD boxes?

thanks for any advice.  If weather is decent tomorrow, I'm going to try again.

thanks.

John

  • Re: Ohm'ing Ignition coil - High Side

    by » 2 years ago


    Section 3.12 of the heavy maintenance manual has the resistance limits:

    Secondary ignition coil
    high voltage - High v. 6.1 to 6.7 kΩ
    Resistance spark plug connector 4.4 to 6.0 kΩ

    From what you have described, you have effectively measured the 2 plug caps in series with the ignition coil secondary winding which come to approximately 15k.

    If the engine will not start, are you sure that you have a spark?

    Which SMD units do you have? The older ones with the individual 'bullet' style coil connections or the multway plug? If it is the individual coil connections, make sure you haven't swapped them over otherwise you'll be firing at the wrong time.


    Thank you said by: John Walsh

  • Re: Ohm'ing Ignition coil - High Side

    by » 2 years ago


    Thanks Kevin.  Yes, I've got the older style bullet connectors.  It does make sense that I measured in series with each cap adding 5k ohms, so the 16.1k Ohm I read seems correct.

    I'm going to remove the SMD's and re-check that the yellow wire connects to the #1 and #2 ignition coils.


  • Re: Ohm'ing Ignition coil - High Side

    by » 2 years ago


    I had them swapped.  Engine runs good now, although I now need to balance the carbs.  Too bad the SMD's are so expensive, I can see why it would make sense to upgrade to the newer style boxes and connectors.  I think the older replacement SMD's (like mine) are about $750 each.  The newer style are closer to $1000 each. 


    Thank you said by: Wayne Fowler

  • Re: Ohm'ing Ignition coil - High Side

    by » 2 years ago


    Hi John

    Just a note on the SMD.  In 2010 Rotax introduced a new part number for the module that has internally a soft start feature.  It can delay the start advance timing from 3 to 5 seconds if you connect it with a power lead from your start solenoid.  (wire diagrams in the installation manual) If you do decide to replace them its best done as a pair to balance the start timing.  I don't recommend mixing old and new versions

     

    Cheers


    Thank you said by: John Walsh

  • Re: Ohm'ing Ignition coil - High Side

    by » 2 years ago


    John, people here in the UK are replacing their Ducati modules with Ignitech units. At 320 GBP per pair they are good value. There are quite a few of these installed and flying around now and they have approval with the UK BMAA and LAA organisations.


    Thank you said by: John Walsh

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