Fluctuating EGT

[PaulB]

My engine monitor has started acting oddly recently.  My number two EGT has started going up and down about 10 degrees.  This is fairly obvious in normalize mode.  From what I read a failing exhaust value tends to fluctuate more than this and is more rhythmic in the changes. Here's a video of it.  

 

http://youtu.be/qUfwuRC132g

 

You'll probably notice that EGT 1 is absent.  The probe died on me on the way to Oshkosh and has since been replaced and is working well.

 

My thoughts are that this is an early sign of the #2 probe going bad, some other wire harness issue, (in distant 3rd) the exhaust valve slowly biting it.  I tried switching the #2 and #4 EGT probes but wasn't able to reproduce it on the ground.  Anyone else have any thoughts on this?

[N201MKTurbo]

I don't think the temperature can change that fast. It must be a bad connection.

[Mike A]

Here is what a leaking exhaust valve (#2) looks like:

https://www.savvyanalysis.com/flight/485434/10d6f522-68b6-4bda-b653-40fe104854d9

 

This cylinder failed its compression test the next month with leakage past the exhaust valve.  I was told you should expect about a 1 minute temperature cycle for a failing exhaust valve.

[KSMooniac]

It could be three things IMO... a failing probe, a poor connection between the probe and harness (loose, or star washer not between the ring terminals), or a spark plug beginning to fail.  I've had plugs going weak that caused some irregular EGT jumping like that... you might do a high power LOP mag check in cruise and see if you can get a plug to drop out and cause noticeable roughness.  If you pass the LOP mag check, then you could swap plugs and see if the behavior follows it.

[romair]

Bad connection. Moving too fast for a combustion event to oscillate like that

[PaulB]

Thanks guys.  That's what I figured.  The same flight from the video I did a LOP mag check and it did just fine.  

[PaulB]

Just an update if anyone else ends up with a similar problem.  I disconnected #2 and switched it with #4 and then back again.  Seems to have solved the problem.  I believe it was as mentioned above: a bad connection.