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Wondering if anyone cares to help me do the right ignition debug sequence for 912ULS. The ignition debug procedure still gets my head spinning a bit.

Runup 4000 RPM resulted in a “miss”, roughness on the B switch but with only a moderate RPM drop (100-150). Sometimes ran smooth for 10 seconds or so, then missing a bit. Checked all plugs. Looked clean. Plugs have 50 hours on them. Checked all plug connections OK. New plugs on order anyway.

  1. Ran test with choke/starting carbs full on. No apparent change. B switch still rough, but no better/worse.
  2. Swapped horizontal connectors. Issue moved to A switch.
  3. Moved horizontal connectors back and swapped vertical connectors. Issue moved to A switch. (Seems wrong somehow that both 2 and 3 would result in switch?).
  4. Swapped P leads, issue moved to A switch.
  5. Pulled one trigger coil wire for A module - B switch/A coil 500RPM drop. A switch OK.
  6. Pulled other trigger coil wire for A module - B switch/A coil 500RPM drop. A switch OK.
  7. Swapped Red charging coil wires - Issue moved to A switch
  8. Checked resistance on Red wires. 3.9-4.1 Ohms.
  9. Put all back to normal. Issue seemed to temporarily be gone or very intermittent now. Need another test to confirm.

Wondering first if I wrote everything down right. Is it logical for the issue to have moved in the way I described at each step? Then, of course, what specific thing might I implicate?

  • Re: 912 Ignition debug procedures

    by » one month ago


    I have no specific knowledge of the Rotax 912 ULS ignition system - In mystery cases like this, I  progressively go through the following (any order, I prefer spending money last)

    # Make sure all earth (-) returns are clean, tight

    # All posative connections are clean & tight

    # Cables (particularly joins) are not subject to being moved ie by some other component/air blast 

    # Multi connection plugs are as above and there is no moisture trapped within

    # All relevant cables are free from abrasion (insulation is in good condition) and continuity has been checked (while moving the cable)

    # Replace plugs - on rare occasions, even a new plug can be faulty

    Are you using AvGas? 

    "1. Ran test with choke/starting carbs full on....."

    Don't understand what you are saying - please rephrase

     


  • Re: 912 Ignition debug procedures

    by » one month ago


    If you get inconsistent results swapping things then I would start suspecting the wiring harness since no matter which plugs you have swapped you will have tugged on all of the wires. I would carefully inspect the connectors and make resistive measurements of all the circuits from the connector and ’manipulate’ the wiring to see if you can detect a broken wire. 


  • Re: 912 Ignition debug procedures

    by » one month ago


    Thanks for the replies. I agree, checking the grounds and connectors should be part of my procedure.

    I should have been more clear on what I was asking. I assumed that others were familiar with the test sequence taught by Lockwood in their maintenance course. I suspect others use it as well. The purpose is to pinpoint where in the ignition (or carburation) an issue might be by methodically swapping connections in the system. If performed correctly, it should be possible to determine the area on the ignition diagram where an issue lies.

    The "choke test" is a means to distinguish between carburation and ignition issues. If adding full choke (which as we all know is not an actual choke) significantly improves or worsens the issue, then the problem may be in carburation and not ignition.


  • Re: 912 Ignition debug procedures

    by » one month ago


    Hi Robert,

    I have often seen references to Lockwood but to date I know of no such agency in all of Australasia 😇


  • Re: 912 Ignition debug procedures

    by » one month ago


    The Lockwood test sequence as in their video is only valid if your modules have 2 x 6pin connectors.

    If you try to adapt it to the older 6 + 4 + 1 connectors it's misleading. Took me a while to realise.


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