EGT Bump during climb

https://www.savvyanalysis.com/flight/1336878/1a412e71-9a52-44b8-ad4e-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?

First flight of the day, starting with a cool engine? Could this be "morning sickness" on the #4 exhaust valve?

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.

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.

airguy said:

First flight of the day, starting with a cool engine? Could this be "morning sickness" on the #4 exhaust valve?

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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.

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

CFI1513840 said:

What would happen to CHT with a sticky valve?

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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.

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.

What ignition system?

I had a simular problem that turned out to be one pmag mag was three degrees retarded.

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.

Change plugs in #4 cylinder and capture more data.

Egt bump

Swap #4 plugs to another cylinder to see if problem moves there.

Don Broussard

RV 9 Rebuild in Progress

cajunwings said:

Swap #4 plugs to another cylinder to see if problem moves there.

Don Broussard

RV 9 Rebuild in Progress

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When I reinstalled the plugs I swapped cylinders 3 & 4. It will be interesting to see what happens when I fly it.

CFI1513840 said:

Here's another data point: when the problem occurs, there is no noticeable affect from the engine, either performance, sound or roughness.

Click to expand...

I don't believe that you would notice one plug dropping out at higher RPMs. Did you check the resistance of plugs and wires. That would be my recommended next step.

Larry

You have a plug problem, or it's related plug lead or distributor post or if on an EI the coil connection/coil.

Most likely the plug.

The correct method of test is to do an in flight mag check during the climb when it occurs. Then you will know exactly which plug.

Correlation with RPM

Further testing yesterday after the plug swap. I leveled off at about 2000' for a couple of minutes, then continued the climb. When I advanced the RPM to 2700, EGT4 immediately began to rise. My practice has been to climb at WOT and full RPM until the MP drops to 25", then dial back the RPM to 2500. Yesterday, I happened to be watching EGT4 when I reduced RPM and noticed the decrease in coincidence with the RPM. Today, I went back to SavvyAnalysis.com and looked at a couple of other previous flights and the exact same thing happened. The EGT4 return to normal always occurs in coincidence with the RPM reduction. This only seems to make this anomaly more baffling to me, but maybe somebody out there can make some sense of it. I'm also going to run this new finding by SavvyAnalysis.com to see if they can come up with anything.

I plan on doing the in-flight mag check to further isolate the problem.

My main concern here is if this issue is a symptom of something more serious and whether it needs to be identified and resolved in the interest of safety.

CFI1513840 said:

Further testing yesterday after the plug swap. I leveled off at about 2000' for a couple of minutes, then continued the climb. When I advanced the RPM to 2700, EGT4 immediately began to rise. My practice has been to climb at WOT and full RPM until the MP drops to 25", then dial back the RPM to 2500. Yesterday, I happened to be watching EGT4 when I reduced RPM and noticed the decrease in coincidence with the RPM. Today, I went back to SavvyAnalysis.com and looked at a couple of other previous flights and the exact same thing happened. The EGT4 return to normal always occurs in coincidence with the RPM reduction. This only seems to make this anomaly more baffling to me, but maybe somebody out there can make some sense of it. I'm also going to run this new finding by SavvyAnalysis.com to see if they can come up with anything.

I plan on doing the in-flight mag check to further isolate the problem.

My main concern here is if this issue is a symptom of something more serious and whether it needs to be identified and resolved in the interest of safety.

Click to expand...

Still looks like a spark issue. The problem you are looking for is increased resistance in the circuit. Your seeing the issue when it is hardest for the spark to jump the gap and the likely culprit is high resistance somewhere. The extra resistance is low enough to allow a spark to jump when easy, but high enough to not allow the spark when conditions are making it difficult (altitude, load, etc.). The plug is certainly one area that can cause this, however the wire, the connector (including the spring) and the cap/spring can all cause problems, as well as the rotor and cap inside the mag (you can't see it, but it is just like a cap and rotor in a 70' vintage car)(you would be looking for erosion or carbon tracking on post associated with the #4 lead) assuming it's coming from the mag. Could also be a wire or the contact inside the coil of the EI. A mag check during the occurrence will tell you which one is causing the problem and where to test.

I notice the spiking RPM while this is happening. Where is your EMS getting it's RPM signal? If it is pulling it off the mag P lead, this is further evidence that one of the mag's plugs is not firing (likely intermittently), which is likely caused by high resistance in the circuit.

You need to do more testing here. You should also be platting MAP, as I think you will find this problem may correlates with altitude and MAP. I will also say that the correlation with RPM points me to the cap/rotor in the mag. Problems there tend to get worse with higher RPM. However, that could still be a symptom of a high resistance problem somewhere else

Larry

In-flight Mag Check, etc.

I agree, it definitely looks like a spark issue. I'm reluctant to do an in-flight mag check at full power, which is where this problem always occurs. It seems pretty clear that one plug is not firing when the problem occurs, which means I would subject the engine to a sudden loss of one cylinder at a high power setting. Also, I wonder what would happen when switching back to both. It seems like for cylinder 4, it would be the same as switching the mags off during the runup, then back on. Probably everyone has done this inadvertently on at least one occasion and we know the results are not always pleasant, which is why I would hesitate to do it under full power while airborne.
I think I should attempt to do the trouble shooting on the ground as much as possible.
I'll check the Dynon EMS RPM wiring setup, but I think that both the mag and the EI are wired. I'm not sure which one the Dynon uses. I can disable them one at a time to find out if it affects the spiking.
The EI uses two coils, each coil fires two cylinders, twice per cycle (wasted spark). Therefore, if the coil was the culprit, I would expect the problem to occur on both cylinders.
I'll start by checking EI leads and swapping them around. If that doesn't narrow it down, I'll move on to the mag.

I would be doing all of this testing on the ground with an ohmmeter. Faster and cheaper. If all tests good, pull the mag and look at the cap. Pretty easy to do. Just be sure to read details on how to reassemble. Assuming the wire and plug on the EI side tests good and the connections seem sound, odds are high the problem is on the mag side.

Problem Resolved (hopefully)

Thanks everyone. I appreciate all of the inputs. Taking the lead from some of the suggestions, I found that the spark plug wires were not seated properly on the Electronic Ignition Coil terminals. The rubber insulators are very tight and it takes quite a bit of pressure to seat the wire connectors on the coils. When they are seated properly, you get a little metallic click sound. I noticed this while in the process of swapping two of the spark plug wires for troubleshooting. It became obvious that the terminals were not making full contact with the coil terminals, lacking up to 1/4" from being fully seated. I then reseated all of the spark plug wires. I test flew it this morning and the EGT4 anomaly has gone away. All EGTs appear normal during climb and cruise. I hope this resolves the problem, but I'll keep an eye on it. I'll also check the spark plugs leads very carefully each time I have the cowling off.