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80 hp 912 UL one EGT went sky high

in General Tech Discussion 10 years ago
This is a new problem and has never happened before. 2007 engine with 344 hours and the carbs have not been rebuilt yet. I was in the pattern today doing touch and go's. On the second climb out the red light was flashing and I saw the EGT for the right bank was off the charts, high. It was a cool evening close to sunset and when I fly alone the EGT's barely make a blip on the digital readout. I immediately came off of the gas/fuel and made a turn to set up a glide back to the runway. But the EGT went down to normal very fast. So I continued on the downwind leg and decided to try full throttle, flat and level. The same thing happened. I continued the pattern with the EGT's normal after that try and stopped flying. I didn't want to pull plugs on a hot engine so I just let the plane sit for the night. I'm thinking to pull the plugs in the morning and see if they are white on one side. Then start in by pulling the float bowls and look over the floats and the main jets. And possible air leaks on the carb boots.

Any suggestions are welcome.

  • Re: 80 hp 912 UL one EGT went sky high

    by » 10 years ago

    What was the EGT that was off the charts?
    Pull the plugs as you said and take a look.
    You could have just a bad EGT probe. I would check this before anything else. Swap the probes or just unplug one and plug the wire into the other probe wire and see if the problem follows the probe. If that's the problem then just replace it for around $30. If this isn't it then check and see if you have an air intake leak. Really check the rubber carb flange well for cracks. They can be hidden and when under a lot of vibration or stress under a high throttle setting may open up enough to suck in air and lean things out.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report

  • Re: 80 hp 912 UL one EGT went sky high

    by » 10 years ago

    I checked both carb boots inside and out very carefully yesterday and they were fine. I also pulled the float bowls just for a look see. As usual they were spotless and the floats worked fine.

    Not sure what you mean by what was the EGT that was off the charts? The temp scale went all the way up and the alarm was gong off on the AMPtronic glass engine panel. I flew the pattern again yesterday convinced that it is a probe problem. If I did not go to full power the engine ran much cooler but the right side was always reading 5 to six times the left side reading.After the 3rd T&G the CHT of the Right side set off the alarm again as I tried full power.

    So buying a new set of probes is the quickest and easiest way to check this out. The current set are 7 years old.

    Thanks for the reply.
      
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  • Re: 80 hp 912 UL one EGT went sky high

    by » 10 years ago

    Checking the OHM readings on the two K type thermocouples between the two leads disconnected from the module, I get no reading whatsoever. That is the same on both thermocouples. Then on the yellow lead on both I get nothing to ground, but on the red lead on one I get a very low ohm reading and on the other I no reading, to ground.

    I ordered new thermocouples and they are arriving today. I am anxious to see if I get normal EGT readings on both sides or if both are high. One came loose from the exhaust pipe reasonable easy, but the other one is not budging. I sprayed a penetrating oil on that one and it has been two days so we shall see.

    In thinking about this I have always burned non ethanol 90 octane or better, fuel since the engine was new in 2008. Recently I changed to Auto fuel, 87 octane w/ethanol due to availability and pricing. And that's when my problems seem to have all started. Could just be coincidence or not.
      
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  • Re: 80 hp 912 UL one EGT went sky high

    by » 10 years ago

    Coincidence. Auto fuel with ethanol didn't cause the EGT probe to go bad. If that were the case thousands of engines around the world would all have issues.

    On the one that feels stuck. Just twist and turn and wobble and it will come out. It most likely just has a little exhaust build up on it.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report

  • Re: 80 hp 912 UL one EGT went sky high

    by » 10 years ago

    I'm really sorry if I was giving the impression that I thought the bad probe was the fault of the fuel. Not at all.

    The high EGT reading started after switching to auto gas. Previously the EGT readings were very low. Too low in fact now that I think about it.

    In any event I will change both probes out and move forward with the EGT reading that I find at that time.

    The one probe has a nut that is stuck fast. I'l bring a hot air gun and try to heat the collar and see what happens. I don't want to screw up the part of the pipe the probe is mounted into. I wonder if my using a small Oxy. Acy. torch is overkill?
      
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