Why do my EGTs spike on landing?

LesGawlik

LesGawlik

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The last couple flights, my EGTs soar when I pull the throttle back while landing. The EGTs on the JPI rise sharply, and all the columns turn yellow. The rise is equal among all 6 cylinders (O470R). Engine runs fine, but I am concerned that this appears to be an aberration. If I give it a little throttle, the EGTs come down.
 
Define soar. What’s a typical rise in round numbers?
 
CHTs are stable. EGTs to me mean unburned fuel leaving the cylinder and igniting in the collectors/risers. For the life of me, I can't see how that happens.

In terms of absolute numbers, I'm not sure yet. I can tell you that normally EGTs are level and blue on the bar graphs. When landing, the bar graphs go from the bottom of the graphs and blue, to the top of the graphs and yellow. They are about equal, meaning it is not one or two cylinders.

I can get absolute numbers when I download the data. But it's striking.
 
What about idling on the ground at other times? Are your EGTs high then?
 
Everything is normal until short final. CHTs are good-cool, maybe 320-350. EGTs are normal, and respond well to leaning. Full rich, short final, throttle idle and the EGTs spike into the yellow, uniformly and quickly.

I lean a lot on the ground. No problem, nothing unusual.
 
Is it a short lived condition or will it stay there?

First though is a mag issue, EGT will rise if half of your plugs drop out.
perhaps one is mistimed?
 
Much easier if you dump your engine monitor data to Savvy Aviation for us to look at. Fuel flow, fuel pressure, and other parameters are helpful to diagnose.
 
I did. SA was baffled. Perhaps some sort of RF interference. It has happened often. The first time I was landing to get gas. I thought perhaps I had run out of gas, and the mixture was leaning because there was simply not enough flow. I had many gallons, so it was not exhaustion. Fuel flow was okay, so not starvation. Cessna 182 so only an engine mounted fuel pump. No other evidence of compromised fuel flow.
 
LesGawlik said:
I did. SA was baffled. Perhaps some sort of RF interference. It has happened often. The first time I was landing to get gas. I thought perhaps I had run out of gas, and the mixture was leaning because there was simply not enough flow. I had many gallons, so it was not exhaustion. Fuel flow was okay, so not starvation. Cessna 182 so only an engine mounted fuel pump. No other evidence of compromised fuel flow.
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So this is intermittent?
 
I’m puzzled as to why EGT’s would rise with a reduction in power and the mixture control set full rich. If it was just a single cylinder, it would be easier to determine. Given that it’s occurring on all cylinders, my thought is that it’s a fuel related matter and the carburetor might be too lean at idle. If it was a rich idle mixture, the EGT’s shouldn’t rise like that.
 
LesGawlik said:
I did. SA was baffled. Perhaps some sort of RF interference. It has happened often. The first time I was landing to get gas. I thought perhaps I had run out of gas, and the mixture was leaning because there was simply not enough flow. I had many gallons, so it was not exhaustion. Fuel flow was okay, so not starvation. Cessna 182 so only an engine mounted fuel pump. No other evidence of compromised fuel flow.
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The sensor is a thermocouple, so rf interference is unlikely.

Probably not sensor data, fuel flow is good, temps rise. Could something with pulling the throttle back be creating an induction leak, leaning the engine?

Or, with rich fuel and a leaky exhaust valve, combustion occurring outside the cylinder? Not much, but burning off the rest of the fuel?
 
bflynn said:
Could something with pulling the throttle back be creating an induction leak, leaning the engine?
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Part of my thought as well, but it would have to be leaking where the manifold mates to the carburetor in order to effect all cylinders, I would think.
bflynn said:
Or, with rich fuel and a leaky exhaust valve, combustion occurring outside the cylinder?
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A leaky valve wouldn’t explain why it’s occurring on all cylinders.
 
SA said they've seen RFI interference with some engine monitors. Not the sensors, the box itself.

But that's not a satisfying explanation, since if I bump the throttle up a few hundred RPMs the EGTs return smoothly and uniformly down to the blue.
 
How long?
You get a couple seconds of extra rich fuel when you first pull the throttle to idle as fuel flashes of the walls of the manifold. But that would require some air to help the fuel burn...

A lean idle or other combustion issues (weak spark?) can result in "slow burn" combustion events that can raise EGT.

But, I ain't no A&P.
 
Weird.

Is there a common shared ground for the probes that might be, for whatever reason, vibrating open at shutdown?

Did JPI support have an idea? Maybe there's some goofy "bus voltage low" scenario for your unit that only manifests during the shutdown and affects EGT computation or display?
 
My only thought is that at that moment the airplane is pushing the prop instead of the prop pulling the plane. In that case the engine is lean as there is a lot of intake air but little fuel flow. But that wouldn't explain it being intermittent. So I chimed in to say ... I have no clue but am interested in the reason for this, whenever it is found out.
 
LesGawlik said:
Engine runs fine, but I am concerned that this appears to be an aberration.
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Have you considered contacting TCM tech support and see if they'll look over your data or give you some input on possible cause?
 
I'm thinking a lean idle condition. A lot of planes are run at 1000 rpm on the ground. When you land you pull the power completely. Which on the planes I fly lowers the rpm down to about 700 rpm on the ground. This looks like a carbureted engine, (O470), it probably needs adjusting. I would be less concerned about the high egts at this point and more concerned that the engine might stall at a bad time from being too lean. Such as if you pulled all the power out on final at 500 feet.

I wonder what would happen if you had the engine warmed up, pulled the power all the way back and let it sit there for a minute. See if you see the egts spike?
 
Do you have the CLD warning set low? Which model JPI? I wonder if it's just the rapid EGT drop tripping the delta-F-per-second-per-second "rate" warning?
 
PaulS said:
This looks like a carbureted engine, (O470), it probably needs adjusting. I would be less concerned about the high egts at this point and more concerned that the engine might stall at a bad time from being too lean. Such as if you pulled all the power out on final at 500 feet.
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Seems reasonable to think that the idle is set too lean. Wonder if any work has been done recently that would coincide with the time these spikes started showing up.

BTW, if I'm at 500' on final and the engine quits the runway should be made ... :dunno:
 
Daleandee said:
Seems reasonable to think that the idle is set too lean. Wonder if any work has been done recently that would coincide with the time these spikes started showing up.

BTW, if I'm at 500' on final and the engine quits the runway should be made ... :dunno:
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Set too lean, or plugged. As far as making the runway from 500 feet, depends on what you fly and what the conditions are I suppose.
 
PaulS said:
As far as making the runway from 500 feet, depends on what you fly and what the conditions are I suppose.
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Agreed! I always plan to have enough altitude once on final but on a blustery day as I'm getting tossed around I really hope I don't have to prove it ...
 
EdFred said:
Don't go full rich until you firewall to go around. Problem solved.
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I don’t see how going full rich would cause EGT to rise. But I absolutely agree with what you said. I don’t do the “mixture full rich” at landing. In fact, if I go full rich at idle with carb heat on my engine will complain! If a go around is required it’s, cram, clean, climb! I know my spark plugs appreciate that.
 
leaning will shift the combustion timing to occur later in the exhaust pipes and raise the EGTs.....
 
AlphaMike said:
I don’t see how going full rich would cause EGT to rise. But I absolutely agree with what you said. I don’t do the “mixture full rich” at landing. In fact, if I go full rich at idle with carb heat on my engine will complain! If a go around is required it’s, cram, clean, climb! I know my spark plugs appreciate that.
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Agree, I don’t do the full rich for landing either. I think it’s bad methodology that’s commonly taught, yet I do understand why, as it’s one less thing for someone to forget prior to a go-around.
 
Where is your JPI grounded? It needs to be grounded to the engine case.

F21F154B-19FB-420C-BFE3-82D030F33669.png
 
Look at the amount of free play in the throttle shaft. I had a carburetor once before that went out of round there, and in certain throttle positions that created a vacuum leak along the throttle shaft…
 
PaulMillner said:
Look at the amount of free play in the throttle shaft. I had a carburetor once before that went out of round there, and in certain throttle positions that created a vacuum leak along the throttle shaft…
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I don’t think I'm following you. How could that cause high egts?
 
Salty said:
at the throttle? Isn’t that just a higher throttle setting?
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Air leaks around the shaft will typically not draw in fuel to match. At idle, the fuel is sucked from small ports right where the throttle plate is close to the wall of the carb and an air leak at the shaft just leans.
Here is an explanation of the idle system, but you shouldn't click on the link because it is my video and we don't want people getting rich by putting their videos on POA. (It's a Bing which has a different system for the main fuel, but the idle stuff is the same...)
 
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10-26-22 Flight.png

This is the flight I posted about. I wanted to change the oil, so I took off and went around the pattern once. What you see are 6 EGTs/CHTs plotted against altitude. At 13 minutes the aircraft climbed to pattern altitude. At 18 minutes the descent begins. While the descent is taking place, the EGTs get quite hot. Note that the data box does not indicate the temperatures at the time in question. The temps are about 1400*, which I think are quite hot considering it is at low power. The temp display were yellow, which is unusual.

Low power setting, prop full forward, normal fuel flow, and high and equal EGTs. I don't understand engine operation well enough to explain this.
 
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Do you have an altitude compensating fuel pump? Your mixture is getting leaner in your descent.
 
Those temps seem awfully hot for idle too. I suppose that could be where they are installed, but a 300 degree spike for full power climb seems small.
 
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