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Flying today in my Kitfox SS7 w 912iS at 2500' ft over Lake Havasou. All was well, RPM's were around 5200. For the first time since I owned the plane saw the EGT's creeping up on all cylinders to limits. I got yellow warnings then red high EGT warnings. I landed and checked the engine area then went up again. RPM's seemed low in climb. I switched on fuel pump 2 and got a little higher RPM's. I tried some major throttle changes and it started to act more normal, but RPM's still low and the EGT's in yellow.

I am thinking fuel as that would be the only way to get all EGT's to move together. Thoughts?

  • Re: High EGT's and low RPM

    by » 8 months ago


     Low Fuel pressure = Lean Mixture = High EGT + low RPM.

    The ECU does not monitor the Fuel pressure and assumes a properly timed "Squirt" will deliver the proper amount of fuel.

    What was the Fuel Pressure?

    Check the Fuel Filters.

     


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


    Thank you said by: Paul Depperschmidt

  • Re: High EGT's and low RPM

    by » 8 months ago


    That is where I was leaning as well.  In the past I could get high fuel pressures, but mainly due to water in MOgas hitting the fine paper filter.  In this case if the pressure is up, it is only slightly.  And with both pumps on it runs better.  But it is relatively easy to change out the fine filter so that is the first place to go.


  • Re: High EGT's and low RPM

    by » 8 months ago


    I agree with Bill

    IF you start to see a rise in fuel pressure, it is an indication the fuel filters are starting to become blocked. This is why the Fuel pressure sensor must be installed before the fine filter. 

    Also, do you have a gascolator installed? This should trap most water before it gets to the fine filter which you can then drain out before each flight. 

    Change your fuel filter and report back!

     


    Thank you said by: Paul Depperschmidt

  • Re: High EGT's and low RPM

    by » 8 months ago


    Never has a truer word been spoken!

    Fly the airplane and quit worrying about EGT....CHT and fuel pressures are the most important!

    Mike Bush

    "High EGTs do not indicate that the engine is under excessive stress, but simply that a lot of energy from the fuel is being wasted out the exhaust pipe rather than being extracted in the form of mechanical energy".

    " High EGTs do not represent a threat to cylinder longevity the way high CHTs do. Therefore, limiting EGTs in an attempt to be “kind to the engine” is simply misguided."

    "Absolute values of EGT (e.g.,1,475 degrees) are simply not meaningful and are best ignored. There is no such thing as a maximum EGT limit or redline, and trying to keep absolute EGTs below some particular valueIf you must fixate on those digital engine monitor readouts, fixate on something important, like CHT"

    I provided a link to the PDF that explains this perfectly!

     

     

    24778_2_EGT_Myths_Debunked-EAA_Sport_Aviation_Oct_2010.pdf (You do not have access to download this file.)

    Thank you said by: Paul Depperschmidt

  • Re: High EGT's and low RPM

    by » 8 months ago


    Mr. RTX wrote:

    Never has a truer word been spoken!

    Fly the airplane and quit worrying about EGT....CHT and fuel pressures are the most important!

    Mike Bush

    "High EGTs do not indicate that the engine is under excessive stress, but simply that a lot of energy from the fuel is being wasted out the exhaust pipe rather than being extracted in the form of mechanical energy".

    " High EGTs do not represent a threat to cylinder longevity the way high CHTs do. Therefore, limiting EGTs in an attempt to be “kind to the engine” is simply misguided."

    "Absolute values of EGT (e.g.,1,475 degrees) are simply not meaningful and are best ignored. There is no such thing as a maximum EGT limit or redline, and trying to keep absolute EGTs below some particular valueIf you must fixate on those digital engine monitor readouts, fixate on something important, like CHT"

    I provided a link to the PDF that explains this perfectly!

     

     

    Yep, get all that.  I have attended Mike's class and lived by his teachings.  With the Cirrus that was extremely helpful.  I replaced multiple cylinders based on his teaching.  The EGT's were great for LOP operations.

    With that said, the Rotax 912 was telling me something was wrong.  The EGT's are there to tell you something has changed in the engine operation.  With the 912iS the only mechanism I have to manage is the throttle. With EGT's rising it could not be my mixture operation.  And if the EGT's are rising the fuel/air mixture is changing.  Air was unlikely, and it was across all cylinders at the same time so spark was unlikely.  That leaves fuel.  With less fuel getting in the cylinders the EGT's will rise until peak.  

    Mike's teachings are great, but the Rotax 912iS requires a bit of modification.


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