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Hello, Folks-

 

First, I've used the search function on the fourum (with great success).  I've already followed much of the advice that I've read, and thank everyone for their contributions!

 

The problem is a greater RPM drop on "A": 250 rpm drop on "A" vs the (normal) 150 rpm drop on "B".  Here is what I've done for troubleshooting thus far:

 

1. I replaced all spark plugs with new.  This is the 2nd new set in 10 hours.

2. Swapped modules.  Problem remained on "A".

3. Rang wiring between ignition modules and coils

4. Rang ignition wires across the coils.  All rang good.

5. Removed spark plug connectors connectors anyway, trimmed 1cm from each wire, reinstalled spark plug connectors.

 

This behaves like one plug not firing.  I've not had any available help to troubleshoot, so I haven't been able to identify which spark plug is the culprit. I'd welcome suggestions for the best method to do this - solo.

 

This engine has 156hrs total since new.  Could one loose or mis-adjusted firing coil at the flywheel cause this problem?  I felt each one for security (they all seem tight) but I haven't yet checked the gap.

 

I appreciate any and all suggestions!

 


Jerry Allison

2016 RV-12

X39 - Lutz, FL

  • Re: 912ULS RPM Drop on "A"

    by » one month ago


    If it is an ignition problem, A look at the EGTs should flag the culprit.
    If one cylinder changes significantly Different from the others during a Lane Test, investigate that one.
    You might expect the misfire to be colder, but the fuel charge might be lighting off in the exhaust pipe giving a Hotter indication.
    So the operative word here is "Different" and not necesseraly Hotter or Colder.

    Also keep in mind that you are looking at a waisted Spark Ignition where plugs always fire in pairs.
    It is possible that only One plug is misfiring because it is shorted.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


  • Re: 912ULS RPM Drop on "A"

    by » one month ago


    In addition to Bill's suggestion above re: EGT indications, you could start up and briefly operate the cold engine with only the one suspect ignition circuit ON -- then shutdown the engine and see which cylinder is colder than the others.  Either touch (be careful!), melting crayon/wax, or a thermal temp gauge can be used to check the cylinder or exhaust pipe temps.  You will then know which cylinder is not firing and you will know which ignition circuit/spark plug is not firing.

    I would also take a look at your ignition triggers settings on the flywheel.


  • Re: 912ULS RPM Drop on "A"

    by » one month ago


    Jerry, I am based at KVDF if you need help call or text me 813-928-0461.

     


  • Re: 912ULS RPM Drop on "A"

    by » one month ago


    Thank you Garrett. I'll give you a call tomorrow!


    Jerry Allison

    2016 RV-12

    X39 - Lutz, FL


  • Re: 912ULS RPM Drop on "A"

    by » one month ago


    I'm not an expert but know enough to say that you shouldn't discount the carbs as an issue 


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