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  #1  
Old 06-20-2020, 01:52 PM
RVG8tor's Avatar
RVG8tor RVG8tor is offline
 
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Location: McKinney, TX
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Question CHT Fluctuations

So my #2 cylinder CHT will set off a shock cooling alarm right from the start through the flight. I was fairly certain it was the probe. It would climb several degrees and come right back to what I figured was normal.

I finally go around to swapping the #2 for #4 probes and went for a flight. Much to my surprise the problem did not follow the probe, issue the same on cylinder #2.

I recently had morning sickness on this cylinder and did the ream procedure, exhaust valve was definitely stuck. I had to use a brass drift to get the thing out. After the reaming, smooth as butter. I don't think these two things are related, but maybe.

My only thought is that some sort of electronic interference is causing the fluctuation. Maybe from the plug wire. It the only thing I can think of that would cause this. Today I had a couple of fluctuations with more movement that before. At a steady CHT of 377 I had a swing up to 399 which set off the high CHT alarm.

So as anyone experienced anything similar? Mags are good (Dual Pmags). Just flew today and did a LOP mag check at 8500' and it was good.

I still need to download the data.

Previously this was an intermittent problem, it would be there one flight then not the next, but lately it is there all the time.

Thanks for any help.
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  #2  
Old 06-20-2020, 03:56 PM
Don E Don E is offline
 
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Location: West Chester, PA
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Default Question...

When you swapped the probes, did you take each one loose from its wiring and put it on the other leads, or merely reroute them without taking them off?
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  #3  
Old 06-20-2020, 05:08 PM
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RVG8tor RVG8tor is offline
 
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Default

Quote:
Originally Posted by Don E View Post
When you swapped the probes, did you take each one loose from its wiring and put it on the other leads, or merely reroute them without taking them off?
I just removed the bayonet end at hooked them up to the other cylinder. My logic was if the probe or wiring between the probe and the EMS were bad then the condition would follow the probe. It didn't, so that is whey I am trying to figure out what might cause this fluctuation, electromagnetic interference is all I can think of.

The temperature swings are too rapid to be actual heat changes in the cylinder.
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  #4  
Old 06-21-2020, 08:32 AM
lr172 lr172 is offline
 
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Default

I had a similar problem with EGTs on my new 10. I had bundled the EGT wires with the ignition wires for a short distance. Unbundling solved the problem. Symptoms were a dead giveaway, as the intermittent movements/swings were more rapid than could realistically be produced from normal, operational temp changes. My swings were withing approximately 10% of actual.

That said, I have dual EI and these provide greater spark energy than mags. Not sure this would have occurred with mags.

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Last edited by lr172 : 06-21-2020 at 08:35 AM.
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  #5  
Old 06-21-2020, 01:42 PM
Don E Don E is offline
 
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Location: West Chester, PA
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Default Maybe I?m confused...

Quote:
Originally Posted by RVG8tor View Post
I just removed the bayonet end at hooked them up to the other cylinder. My logic was if the probe or wiring between the probe and the EMS were bad then the condition would follow the probe. It didn't, so that is whey I am trying to figure out what might cause this fluctuation, electromagnetic interference is all I can think of.

The temperature swings are too rapid to be actual heat changes in the cylinder.
If #2 was the squirrely one and you just moved that probe to #4 and #4 probe to #2 without rewiring, then your engine monitor saying #2 is the problem is saying ?the probe now in #4? is the problem. It doesn?t know where the probe is or that it was moved... so therefore the probe or the wiring connection (more likely in my opinion) is the issue...
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  #6  
Old 06-21-2020, 08:02 PM
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RVG8tor RVG8tor is offline
 
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Quote:
Originally Posted by Don E View Post
If #2 was the squirrely one and you just moved that probe to #4 and #4 probe to #2 without rewiring, then your engine monitor saying #2 is the problem is saying ?the probe now in #4? is the problem. It doesn?t know where the probe is or that it was moved... so therefore the probe or the wiring connection (more likely in my opinion) is the issue...
If the probe set up to measure #2 was moved to #4, and it was a bad probe I would have expected #4 to behave the same as it did when installed on #2. It did not so, if I discount a cylinder problem since this kind of swing cant happen with the CHT, then my hypothesis is that something in the ignition wire near the CHT wire is the issue. There is a half loop in the ignition wire just above where the CHT wire is located, it is really too long but I did not make them. This issue did not start in earnest till this year, I have put 640 hours on it since building it, first flight in 2012.

I am going to try and move the ignition wire and see what happens.

I was hoping someone may have had the same issue and could confirm my hypothesis is plausible.

Cheers
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  #7  
Old 06-22-2020, 01:36 AM
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rv8ch rv8ch is offline
 
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Default Engine monitor label

Quote:
Originally Posted by RVG8tor View Post
If the probe set up to measure #2 was moved to #4, and it was a bad probe I would have expected #4 to behave the same as it did when installed on #2. ...
Mike, if you moved the probe without changing any wiring or the label in the engine monitor, then it will look like it's the same cylinder no matter where you put it. So it sounds like it's the probe or the wiring between the probe and the engine monitor.

Perhaps you did rewire, if so, ignore what I said above.
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  #8  
Old 06-22-2020, 03:21 AM
BobTurner BobTurner is offline
 
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If you fly on one mag, does the problem go away?
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  #9  
Old 06-22-2020, 11:11 AM
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RV7 To Go RV7 To Go is offline
 
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Default Check the terminal crimps

I just had an issue with the #1 CHT probe on my Dynon Skyview. After taking off from my destination airport the reading went from my normal 350 ish up over 400 then up over 500. All else was normal so I continued home. After landing, having previously read about many terminal crimp issues, I recrimped the factory crimps on the #1 CHT leads. All back to normal for the last 5 hrs since.
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  #10  
Old 06-22-2020, 11:14 AM
OKAV8r OKAV8r is offline
 
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Default

Check for a bad ground.
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