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-   -   Cylinder 1 EGT and CHT rise and fluctuate (https://vansairforce.net/community/showthread.php?t=180657)

Dayz 03-22-2020 05:08 AM

Cylinder 1 EGT and CHT rise and fluctuate
 
Guys,
I believe we have an issue with our #1. Today at runup our CHT and EGT went up high, faster than the other 3, engine ran not perfectly ( there was a miss if you listened properly).

Everything seemed to stabilize after but stayed higher the whole flight than usual.

Sensors were acting as if they were going bad, giving all sorts of random data?s. But in this case, the miss, and the fact that CHT and EGT were giving random numbers at runup is puzzling me. I pulled the data and will post it if I can figure out how.

I was thinking of pre ignition? But why, I was full rick at idle. Maybe pieces of hot carbon stuck on a valve that would preignite?

Let me know. We need to find this issue.
Thanks

lr172 03-22-2020 07:38 AM

That is a tough one. Struggling to come up with a scenario that would raise both, while causing misses. Pre ignition seems pretty unlikely at runup RPMs with a cold engine in cool weather. Detonation also less likely with a cold engine in cool weather. While I have never observed detonation in an engine with EGT sensors, I would expect that CHT would rise rapidly and speculate that EGT would go down or stay the same. I can't think of a reason that detonation would cause a rapid rise in EGT, unless the combustion didn't fully burn the mixture and it was completing it's burn in the exhaust. I just don't know how likely or possible that is.

Detonation is more of an explosion than a contolled burn. It imparts a great deal of heat into the cylinder due to this, but the burn is shorter and less complete and therefore speculate that it would not create elevated EGT readings. Again, have no real experience with EGT data, so just speculation. Most things that raise CHT above normal, reduce EGT from normal, at least when dealing with large swings.

My experience with detonation has always been under haevy load conditions, like high MAP. There may be some slight roughness, but misses are not common, in my experience. I just can't see how someone could get pre-ignition at 1800 RPM on a cold engine, although I am sure it is possible.

I would definitely start the troubleshooting process with the sensors first.

Larry

mahlon_r 03-22-2020 09:32 AM

Leaky exhaust valve? Partially plugged fuel injector with floating type debris if it's an IO engine?
Stay Healthy,
Mahlon

Dayz 03-22-2020 12:10 PM

Guys,
Here is just after sunup and the first few minutes of test flight. Could it be a little drop of the "Champion Graphite Anti Seize" that would have been too low on the thread? I am puzzle. As you can see, it got better and better.
Thanks Again



Mike S 03-22-2020 12:20 PM

Wild thought here-----any possibility the wires from the CHT and EGT have rubbed together and worn through the coverings-----shorted together???

I had originally thought of an intake leak, but after looking at the graphs, not what I would expect from an intake leak.

lr172 03-22-2020 12:56 PM

Quote:

Originally Posted by Dayz (Post 1416481)
Guys,
Here is just after sunup and the first few minutes of test flight. Could it be a little drop of the "Champion Graphite Anti Seize" that would have been too low on the thread? I am puzzle. As you can see, it got better and better.
Thanks Again




That is a sensor / instrument issue. CHT cannot rise 50 then fall 100* in .5 seconds. assuming those numbers are seconds and not minutes. Note that both EGT and CHT are RAPIDLY oscillating. The actual temps can't realisticly change that fast. The continually higher oscillation rate of #1 vs the others helps to confirm that diagnosis.

EDIT: I now see they are minutes. However, you are still showing a 100* CHT reduction followed by a 100* increase in the neighborhood of 10-15 seconds. That just isn't possible, regardless of what is happening inside the cylinder.

Larry

Don E 03-22-2020 01:05 PM

Check for proximity to spark plug leads...
 
Could be getting voltage bleeding in from a spark plug cable, especially electronic ignition, if these wires are bundled with or too close to one. That could also possibly cause a miss.

Dayz 03-22-2020 08:06 PM

It is an O-360 A1A
No electronic ignition. I will check wires, perhaps both sensors went at the same time.

walkman 03-23-2020 09:03 AM

Quote:

Originally Posted by Dayz (Post 1416481)
"Champion Graphite Anti Seize"

That stuff is horrible. Use a heavy copper based anti-seize instead!

Switched over 20 years ago, never a problem, never a difficult plug.

bjdecker 03-23-2020 05:20 PM

I had the exact same signature -- turned out to be a bad probe. Reterminate the wires just as a sanity check before spending $$$ tho.

Cheers!

B


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