EGT random fast rate increase that also makes your heart rate increase!

[Keenaviator]

I built (ish) a Jabiru UL 450 and now have 260 hours on both airframe and 2200 Jabiru engine.

 

CHT and EGT are only monitored (at this stage) on two cylinders -  no 3 for EGT and no 4 for CHT.

 

Today I was out jollying around for about an hour.  Cruising steadily at 2800 rpm, around 13 litres per hour and EGT on 700 deg C.  Suddenly I notice the EGT quickly rising to about 740.  There was no change in RPM, fuel flow was steady, CHT steady (around 105 indicated), oil temp 90 and pressure steady.  This has happened before, months ago and I have check the induction manifold and tubes, all secure. If there was a problem there I would think it would be more consistent than this apparent spurious reading.

 

Is it possible that a dodgy electrical connection could cause this?  The gauge is a standard VDO display and the sender a K type screw in type.

 

Regards, Laurie

 

 

IMG_2639.heic

[Bruce Tuncks]

Yep, I would suspect the sender first. An electrical connection sure could do that.

I have EGT on all 4 cylinders of my SK jabiru, and I don't use it much now that the 4 cylinders have been equalized. I was surprised how different the cylinders were to start.

I don't see much use in the EGT figures except to show if the cylinders are the same like you want them to be.

Remember you are just reading the average temperature of a probe, and this probe gets a blast of hot gas for 45 degrees in every 720 degrees. Apparently the "real" combustion temp is about 2000 degrees C. So the difference in 700 to 740 is not that much. Did the CHT show a change?

 

 

[facthunter]

It's possible that a slight change in output makes the flame pattern in the port slightly different. Next time it happens move the throttle a bit and see if any change.. Nev

Edited January 4, 2022 by facthunter

[RFguy]

spark/mag/lead/single plug  issue ?

[Kenlsa]

Over the years we have had changes in EGT in our 5 Jabs in our club.
Always turned out to be a sender problem, not anything else. Defected and panic stations for not much….

I wonder if we worry far too much about all these numbers. My Lycoming doesn’t have EGT or MAP…. errr or anything really ….

I just rely on a pull thru before flight, seems to work for me.

Ken

[Keenaviator]

4 hours ago, Bruce Tuncks said:

Yep, I would suspect the sender first. An electrical connection sure could do that.

I have EGT on all 4 cylinders of my SK jabiru, and I don't use it much now that the 4 cylinders have been equalized. I was surprised how different the cylinders were to start.

I don't see much use in the EGT figures except to show if the cylinders are the same like you want them to be.

Remember you are just reading the average temperature of a probe, and this probe gets a blast of hot gas for 45 degrees in every 720 degrees. Apparently the "real" combustion temp is about 2000 degrees C. So the difference in 700 to 740 is not that much. Did the CHT show a change?

 

 

Thanks Bruce.  There was no change in the CHT, RPM or fuel flow.  Laurie

[Keenaviator]

3 hours ago, facthunter said:

It's possible that a slight change in output makes the flame pattern in the port slightly different. Next time it happens move the throttle a bit and see if any change.. Nev

Thanks FH.  I adjusted the throttle, applied carb heat, fuel pump on, confirmed mixture rich and after a minute or so the EGT returned to its normal level.  Laurie

[Mewp]

Occasionally have this problem and found the connection between the probe and the EMS loom bayonet clips at fault. I disconnect and reconnect and all is OK.

[facthunter]

It's probably a connection. We could be fixating on this stuff too much. There's plenty of vibration around  engines. Egt's are more important on 2 strokes and Turbines. Nev