I have a 2019 LSA with a 912IS engine.  Over the last few months on long cross country flights I have noticed a consistent issue.

On my #4 cylinder, at altitude (7,500msl or higher), the EGT temps will slowly rise by themselves and independent of the other cylinders.   This is level cruise, WOT, 5450RPM, full rich.  The other cylinders get to a certain temp and basically stay there without moving.   There may be an 80-100 degree difference between the others, but they don't really move at all.

Over a period of about 10 minutes the temps on the #4 will creep up until I get a warning at 1600f.  If I cut the throttle to 5,000rpm (eco) and then go back to full power, the EGT on #4 will drop back down with the rest.  But over the next 10 minutes it will creep up again.  This cycle just repeats itself.

I have replaced both fuel injectors on the #4 cylinder, but that has not had any impact.  The plugs are new on all cylinders.  After inspection, they all seem fine and consistently colored.

Anyone have any thoughts of what may be going on?  The higher the altitude, the quicker this issue seems to happen.  At lower altitudes, there is less of a spread but as I recall the base EGT for all cylinders appears to be higher.  (I'll confirm later...thats just from memory).

I have new EGT probes, in case it is a simple issue of just the probe.

Should I just replace that one probe on #4 and test, or should I swap the probe with another cylinder? 

My concern about swapping, is that as I recall...messing around with any EGT probe basically causes them to fail shortly after replacing them.   So swapping means I will have to replace two probes vs. just replacing the one I think is bad.

Any other thoughts come to mind?

  • Re: Single Cylinder EGT Creeping Up - Why?

    by » 2 years ago

    Hi Shawn

    I would try a swap of the EGT first.  As for the injectors I doubt they are the issue.  The system reads the EGT and if there was a problem with the injector you most likely would get a warning on your monitor.  Without the engine serial is is difficult to say which EGT you have , early versions on the iS were not as good as the newer ones.  


    I am not sure why you would want to run the engine WOT since best fuel economy is at 97% on the TPS.  



  • Re: Single Cylinder EGT Creeping Up - Why?

    by » 2 years ago

    Thank you, swapping the probes seems to be the most suggested option.

    It's a 2019 plane and consequently a very recent serial number (I don't have it off hand).

    As far as why I sometimes fly WOT, it comes down to a couple of factors:

    1. I'm trying to get someplace quicker
    2. Fuel economy (for me) is basically irrelevant (4 vs 6gph).
    3. When operating in ECO mode between 5300-5400 I do not like to see the significantly higher EGT temps.  I understand many people say that EGT doesn't matter.  However at some point it is too high.  Getting warnings for high EGT means I need to do something and that is either reduce power more or get above the ECO mode to full rich.


  • Re: Single Cylinder EGT Creeping Up - Why?

    by » 2 years ago

    hello Shawn

    the operators manual for the iS allows for a max of over 1700F EGT.  I am not sure why your instrument is giving you a warning at 1600F.  ECO mode is designed to run lean and that implies that it will run near the max EGT in a lean burn.  Perhaps check if you can what the Rotax BUDS readout is inside the computer for any faults in that respect.  

    Just my suggestion is all. 



  • Re: Single Cylinder EGT Creeping Up - Why?

    by » 2 years ago

    Thanks....actually it is my G3X that gives me warnings at 1650 (user defined).  But point taken about running lean and results in a high EGT.

    I guess I could let it continue to climb and perhaps it stops before 1700.

    We did pull the logs and there was nothing of interest...shockingly very little was logged.

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