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spiking EGT!!

prkaye

Well Known Member
Today after a 45 min flight as I throttled back on approach to the airport, my Cyl #2 EGT suddenly started climbing intermittently up well into the yellow, above 2000. Other EGTs, all CHTs and other readings were normal, and I noticed no interruption in power. The Cyl #2 EGT seemed to come back down when I added power, but intermittently climbed up to 2000 and then back down, several times. When I throttled to idle for final and after landing, the EGT readings stayed stable at normal levels.
The flight had been fairly lean, high up on auto fuel (premium, ethanol free).
Any thoughts on what could be the cause? Any suggestions on how to diagnose this and what to look for?
(Probably unrelated, but for quite a few months now I've had an issue with my Dynon LOP/ROP reading - constantly saying LOP even at full rich settings, with all other readings normal including EGTs, and engine leaning properly. This makes me wonder whether I have a defective sensor).
I'm frightened of facing a major engine repair expense.
 
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Check your PMs.

It could be a plug failure or associated harness, or a valve problem.

Please call me, even from Canada:)
 
I would pull the probe and check it out before getting too concerned.

The service record of the EGT probes that Dynon sells is less than stellar.

See this thread.
 
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I will definitely have a look at the probe. But would a failed probe necessarily show any visible signs of failure? I don't think swapping the probes is practical (wire lengths), but that might be an option to test them.
 
I would agree with suspecting the EGT sensor. Is there NO EGT probe that you can swap to that cylinder or move that probe? If you can change, and the symptom moves with the sensor, you likely have the culprit.

There is some chance, possibly remote, that you have an induction leak. I would be more inclined to suspect the probe.
 
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CHTs were totally stable. Spark plugs are all quite new - less than 50 hours on them.
No noticeable change or disruption in engine performance.
If an induction leak, how would I test for that? Compression check?
 
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You can't move the #2 EGT probe back to #4?

As for the induction leak, I believe (get confirmation) that the CHT on that cylinder should rise (if ROP). If that is not happening, move the induction leak possibility way down and concentrate on the EGT probe. Just opinion of course.
 
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I'll go out on Monday and check if I can move the sensor.
Please tell me more about the induction leak... would it exhibit any other symptoms? If I continue to fly with an induction leak could it lead to serious damage? What is the fix?
 
Phil-
Jamie and I are not talking about an inaccurate EGT sensor, we're talking about a burned up one. Pull it out of the exhaust and see what it looks like. If it looks like it's damaged or non-existant, then you've probably found your problem.
Hope this helps.
 
A induction leak is not going to cause a spike above 2000. I am with the others. Pull the probe.

Excellent point George. That is ~400-500 degrees F higher than I ever see. Peak EGT, LOP, ROP.

Just another indicator that the EGT probe is a prime suspect and that Phil should not lose sleep over this.
 
ok thanks guys. This is reassuring. I'm planning to take the day out there on Monday. I'll start by pulling and inspecting the probe, cleaning, checking connections and swapping with the #4 probe if possible. I'll then fly it and see if the problem recurs. I'll report back here.
 
Did it read 2000 exactly?

If so, that may be the Dynon full scale reading, probably indicating either a dead short or an open, depending on Dynons electronics...
 
I can't be sure, it was fluctuating pretty quickly - I think it went over 2000. I'll keep a much closer eye on Monday and if the problem recurs I'll try to get much more data.
 
My Experience

I had a similar issue on a cross country once. I have Lightspeed on the top and magneto on the bottom. I had a wire going into one of the coils get loose in the connector and I had two EGT's go in the red. It was easy to see that two plugs were not firing on the ground. I re-crimped a new connector going into a coil on the Lightspeed and everything was fixed.
But mine was never close to 2000. That sounds like a probe issue.
By looking at the end you may find that it is bad.

My first EGT probes from Grand Rapids all went out pretty quickly. I found out they make a higher temp probe that is a little more money. Since then, no problems.
 
check the connection...

The connections for the EGT are very sensitive since the thermocouple wire is not stranded and very small... they are especially susceptible to erroneous readings when the connector is not well restrained from vibration.

As a side note, Dynon changed out their probes to an Inconel type this past Spring (same part number as the previous probes); they seem to be holding up better.
 
I will definitely have a look at the probe. But would a failed probe necessarily show any visible signs of failure? I don't think swapping the probes is practical (wire lengths), but that might be an option to test them.

Check out the link I posted above for pictures indicating the failure mode.
 
Is it even possible to reach 2000 degrees on gasoline? And if so, would you still have an exhaust stack on that cylinder, or just a melted blob?

I'm thinking you have an indication problem.
 
Been there before

When a EGT probe becomes "open" the Dynon will read 2000 degrees.

After a few hours on the RV one EGT reading would swing wildly from normal temps to 2000 degrees in a matter of a second. I called Dynon and they didn't have a good answer. They didn't know that an "open" would cause this reading.

I pulled the cowl off turned the Dynon on and started wiggling the connections. When I did the EGT wire at the factory crimped spade lug fell out. I crimped on a new lug and everything has been fine for the last 120+ hours.

I also checked all the factory crimps to make sure there wasn't another connection ready to fail.
 
thanks again guys - i'm looking forward to getting out there tomorrow and investigating the probes and connections. I'm thankful this happened at the end of a flight as I arrived home, and not way out West on my long trip - that would have made the return portion of my trip very stressful!

swing wildly from normal temps to 2000 degrees in a matter of a second
I don't think mine climbed quite that fast... probably took 2 or 3 seconds for it to climb to 2000. It certainly wasn't an instantaneous jump. If a connection was shorting-out or coming loose, wouldn't that cause the reading to instantly jump?


It was easy to see that two plugs were not firing on the ground.

What is the best way to diagnose this? How do you best determine if all plugs are firing or not?
 
With the engine running, simply turn off one ignition, then the other. If you have a dead plug, that cylinder will die as well.
 
I'm thankful this happened at the end of a flight as I arrived home, and not way out West on my long trip - that would have made the return portion of my trip very stressful!

No need for stress. How many planes have no EGT reading or on just one cylinder?

All other indications were good.
 
With the engine running, simply turn off one ignition, then the other. If you have a dead plug, that cylinder will die as well.

Cool, thanks. I actually do this as part of my standard run-up check before the first flight of every day, although I have to admit I don't actually look specifically at CHT's when I do this. I just do the mag check to be sure the engine keeps running nicely.
 
I had almost the exact same thing yesterday on my #2 cylinder (was able to keep it out of the red). I suspected probe too and kept on trucking. No secondary indication of an issue and a buddy of mine was complaining last year of EGT probes failing this way. I'll pull the cowl before next flight to see if I can diagnose, I'm sure I'll be ordering a new probe.
 
EGT is primary on pre T. O. checks

although I have to admit I don't actually look specifically at CHT's when I do this. I just do the mag check to be sure the engine keeps running nicely.

I agree with the focus on what you hear, smooth running. Also, on my run ups I consider the EGT readings the primary place to spot problems during the single ignition operation; the CHTs can not easily reflect abnormal results from the short time you should run on 1 ignition. BTW, I can't believe so many posted answers and failed to note that 2000 on an EGT reading is certain instrument error on a conventional piston engine, regardless of any possible mechanical failures. And on the issue of how fast it flashes to 2000; it's all a matter of the quirks in a wire failure - can be immediate or can flcker - lots of variation, the common element is abnormal readings.
Sounds like the gang has this one sited in.
 
So today I went out first thing in the morning. I took the cowls off and went about inspecting the suspect EGT probe on the #2 Cylinder. I removed the clamp and pulled it part-way out, and then it stuck. I couldn't get the probe out, no matter how much I wiggled, twisted and pulled, even with plyers. I asked an AME (Canada's A&P designation) in the hangar next door, and he agreed that the probe is probably what caused my abnormal reading.
Now here's the bad news - during my work, I got careless and a tool slipped and nicked the bottom of my oil cooler and put a little hole in it. So now I have to either replace or repair my oil cooler :(.
So at that moment I decided that I may as well shut it down for winter a month early. It's rapidly getting too cold to work comfortably in the unheated hangar, and I was planning on pickling it this winter anyway and sending my nosewheel in for the bearing mod.
So, I re-secured the probe (I'll cut it off in the spring when I get new ones). I drained my oil and added 5 liters of Aeroshell 2F, and did a 15 min ground run. During the ground run I did a couple of extended mag checks, also checking leaning on both mags independently. EGT indications were totally normal, including the expected rise during leaning on each cyl. I guess it was just a quirky reading on Sat.
So, I did the rest of my winter prep (still need to get dehydrator plugs) and removed my nosewheel. Now I need to start researching whether to replace or repair my oil cooler and I need to research a source for new EGT probes.
Could have been a lot worse. I shouldn't complain - in over 2 years and 150 hours I really haven't had many problems.
Thanks for all your advice here on the EGT issue!
 
Cool, thanks. I actually do this as part of my standard run-up check before the first flight of every day, although I have to admit I don't actually look specifically at CHT's when I do this. I just do the mag check to be sure the engine keeps running nicely.

If you're running one ignition OR the other and find a dead plug, you will not have to look at any instruments to know you have a problem! After that, it is easy to spot which out of the four are dead - the EGT will plummet immediately.
 
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