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  #1  
Old 06-06-2016, 11:04 AM
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CFI1513840 CFI1513840 is offline
 
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Default EGT Bump during climb

https://www.savvyanalysis.com/flight...e-e80cf2eb56e5

On a few occasions during initial climb I experienced an increase in EGT 4 of about 60 degrees over a period of a minute and a half, followed by an abrupt return to normal. This usually happens about the same point in the climb. SavvyAnalysis.com identified this as an ignition/spark plug problem and I agree with them. But what is a mystery to me is why is only lasts for a minute and a half and why it always occurs at about the same point in the climb. Could it be temperature related? Any ideas?
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  #2  
Old 06-06-2016, 12:35 PM
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airguy airguy is offline
 
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First flight of the day, starting with a cool engine? Could this be "morning sickness" on the #4 exhaust valve?
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  #3  
Old 06-06-2016, 01:26 PM
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CFI1513840 CFI1513840 is offline
 
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Default Correlation with CHT

The reason that Savvy suggested ignition/spark plug problems was the slight depression of the CHT relative to the other cylinders during the event. The EGT would rise with a burned exhaust valve, but the intermittent nature would point to a sticky valve rather than burned. What would happen to CHT with a sticky valve?

Maybe ignorance is bliss. I never worried about this stuff before all this fancy instrumentation.
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RV-7 N92LT - Based at Thomson-Mcduffie airport HQU
TMXIO-360, Dynon Skview
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Last edited by CFI1513840 : 06-06-2016 at 01:37 PM.
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  #4  
Old 06-06-2016, 01:28 PM
BobTurner BobTurner is offline
 
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Define "abrupt". If you mean instantaneous, then you're looking for a poor connection. The probe cannot respond instantaneously. If the wires are long enough, swap #2 and #4 EGT probes, wires and all, and see if the issue stays on #4 or moves.
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  #5  
Old 06-06-2016, 01:48 PM
bjohnson1234 bjohnson1234 is offline
 
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Quote:
Originally Posted by airguy View Post
First flight of the day, starting with a cool engine? Could this be "morning sickness" on the #4 exhaust valve?
SavvyAnalysis has a "failing exhaust valve analytics" that runs every time you upload your flight data, even if you don't submit it for full analysis.
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  #6  
Old 06-06-2016, 02:01 PM
lr172 lr172 is offline
 
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I don't see how it could be temp related. More likely pressure related. If it were all cylinders, I would say you had an issue with your ignition advance table. I am struggling to identify what would cause retarded timing in only one cylinder. I would consider looking at ignition wires and plugs for #4. Its possible that high resistance is causing the plug to fire late. Lower pressure makes it harder for engery to jump the plug gap, making it loosely altitude depend. It's a long shot guess, but I'm otherwise at a loss,. especially given the fact that it rectifies itself. It looks a lot like a failing pressure sensor on your EI (forcing the retarded timing), but that would affect all cylinders.

I don't see how an exhaust valve could produce that cycle of symptoms consistently.

EDIT: Thought about this some more (I wasn't thinking dual plug). You need to test the wires and plugs on #4. If one plug fails to ignite, your relative timing for that cylinder is retarded and will cause the symptoms that you have. Lower ambient pressure makes it harder for the energy to jump the gap on the plug, therefore showing the symptoms on climb. I can't explain why it starts firing again, but it is the mostly likely culprit for your set of symptoms.

Larry
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Last edited by lr172 : 06-06-2016 at 02:20 PM.
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  #7  
Old 06-06-2016, 02:16 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by CFI1513840 View Post
What would happen to CHT with a sticky valve?
A burned or sticking valve should reduce CHT. The more air fuel you get into a cylinder, the more heat it will produce. The more that heat is retained in the combustion chamber to produce piston movement, the higher the CHT's. If you let some of the heat out (burned valve, broken ring, etc.) the CHT's go down. In the case of a burned valve, your letting the heat into the exhaust instead of piston movement, therefore EGT's go up, CHT's go down and Power goes down. Sticking valves can be tricky, depending upon whether they allow enough pressure on the compression stroke to allow ignition.

Retarded timing has the same effect. EGTs go up and CHT's go down as the late ignition doesn't allow as much heat to be converted to piston energy and is retained in the exhaust, raising EGT.
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Last edited by lr172 : 06-06-2016 at 02:22 PM.
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  #8  
Old 06-06-2016, 03:55 PM
Mike H Mike H is offline
 
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A burnt exhaust valve will most definitely cause a high CHT indication due to extremely hot combustion gasses leaking between the valve and the valve seat.

A sticking valve usually causes low CHT due to combustion pressure reduction but it depends on how far off of the seat the valve is when it sticks. Sometimes a sticky exhaust valve that is not seating all the way does in fact turn into a burnt valve.
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  #9  
Old 06-06-2016, 04:20 PM
RetiredRacer RetiredRacer is offline
 
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Location: Ipswich QLD Australia
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Default What ignition system?

I had a simular problem that turned out to be one pmag mag was three degrees retarded.
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  #10  
Old 06-06-2016, 05:55 PM
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Default EGT 4 Anomaly

I should mention that I'm running one mag and one LSE EI. Also that I changed out the probe on EGT 4 last year. In that case there were obvious indications that the probe or wiring was bad as the EGT was jumping all over the place. After changing the probe, it settled down and gave solid readings. The "bump" I have noticed recently was easy to overlook, but in reviewing some of my old data files, it's obvious it has been around for some time, even before the probe was replaced. I think the earlier probe problem and this problem are two different issues, but the mystery remains. I'm not ruling out anything, valves, timing or otherwise. I just cleaned and gapped the plugs, and checked EI timing which appears to be ok. I did notice a small amount of crud in the mag driven plug on cylinder 4, but don't know if it was enough to cause misfiring. I'll fly it to see if cleaning the plugs had any effect.
If you look closely at the plot, you'll see that CHT 4 decreases coincident with the rise in EGT 4, which reinforces Savvy's contention that the indications are real and not a sensor issue.
Here's another data point: when the problem occurs, there is no noticeable affect from the engine, either performance, sound or roughness.
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Ken Howell
Evans, Georgia
RV-7 N92LT - Based at Thomson-Mcduffie airport HQU
TMXIO-360, Dynon Skview
Flying since June, 2012

Last edited by CFI1513840 : 06-06-2016 at 06:03 PM.
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