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EGT question

jwilbur

Well Known Member
I have a question for the community here. At a certain MAP my #1 EGT goes up 50 degrees. This has happened ever since first flight. It doesn't appear to be causing me any issues. An example of when it happens is when I pull power in the pattern to start a descent. Periodically, I've tried to figure it out. I've cleaned injectors, I've searched for intake leaks, I've gapped and cleaned and eventually replaced plugs. Nothing changes the behavior. Does anyone have any ideas? And are there any opinions on what long term impact (if any) there might be on my engine. See chart below for a nice example.

Bottom trace is MAP. Top traces are EGTs. #1 is the one that stands out from the others.

egq_and_map1-1.png
 
Perhaps induction related?

It's either going to be a probe, induction or fuel delivery issue.

That first dip is telling and given the gradual and almost synonymous change relative to throttle setting I'd be suspecting the fuel delivery system. Perhaps some crud in the manifold spider as others have been experiencing here of late?

You could verify this and the integrity of your #1 cylinder probe by swapping it with another cylinder.

http://www.vansairforce.com/community/showthread.php?t=182191&highlight=Spider
 
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It's not the probe. It tracks the others perfectly at high power. Can anyone say more about the spider? How do you inspect/clean that? Does it make sense to switch the injector nozzles with one of the other cylinders? That's something I've never tried.
 
It's not the probe. It tracks the others perfectly at high power. Can anyone say more about the spider? How do you inspect/clean that? Does it make sense to switch the injector nozzles with one of the other cylinders? That's something I've never tried.
What you described about tracking the other cylinders is not proof it is not the probe. Try swapping the probe to another cylinder then see if it follows the probe.

As for the spider, it is easy enough to remove the top of the spider to peer into it. However, there is an extremely fine mesh screen in there that is extremely difficult to remove without damaging it. Go ahead, ask me how I know. And just to be sure, I also can tell you that replacing that very fine screen is not cheap either.

So having said that I would NOT start with the spider. I would 1.) swap the probe and see if that is the problem. If not, 2.) check your fuel filter(s) for any type of debris. 3.) Switch the injector to another cylinder and see if it follows the injector. 4.) Since you would have the injector off, clean it (and all the others for that matter). You can do so by soaking it with some Hoppe?s #9 gun cleaner. Preferably in an ultrasound cleaner.

Good Luck, keep us updated on what you find.
 
It's not the probe. It tracks the others perfectly at high power. Can anyone say more about the spider? How do you inspect/clean that? Does it make sense to switch the injector nozzles with one of the other cylinders? That's something I've never tried.

Each output of the spider has a V shaped orrifice. Its main purpose is to meter fuel (technically it is to increase pressure) at and somewhat above idle. Partial blockage at the very bottom of the V would cause lean running for that cylinder only at low MAP levels. It could also account for the very slightly lean condition you are seeing at high MAPs. This is somewhat common with new spiders or fuel systems - debris from manufacturing . Even very small debris can cause this

It is easy to take apart and clean if you are competent and careful.

Larry
 
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It's not the probe. It tracks the others perfectly at high power. Can anyone say more about the spider? How do you inspect/clean that? Does it make sense to switch the injector nozzles with one of the other cylinders? That's something I've never tried.

It's all in the link I put there for you.
 
I don't have a brilliant answer or cure to the current pandemic but I have an observation.

Middle of graph, the EGT #1 delta is approx 50F. Not significant.

Right of graph EGT #1 matches closely the EGT #2 and follows the general trend. Again not significant.

Left side of graph initial dip with 200F delta mellows out in 20 seconds.

My observation is 30 years ago this level of "granularity" of data was unheard of. Second on your comment, "It doesn't appear to be causing me any issues", you have your answer. Don't worry about it, and fly more and plot graphs less.

I don't agree it can't be probe based on high power tracking.... it could be the probe. It may be more sensitive to the changes at low power, for a few reasons, one being how and where it is installed in the pipe. What kind of pipes are on that 540? Scavenging could be different and if probe is not same place (thermally) in the pipe as the other jugs, it could affect this LOW PWR reading. It could be at low fuel pressure that jug is getting a tad less fuel. (Wild guessing switch off)
 
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Look again for an induction leak on the pipe to #1. Maybe at a slip joint, maybe at the cylinder flange. With the engine running, carefully spray alcohol on the intake joints and see if egt changes.
 
Anytime you suspect a spider issue, do the simple shot glass test. Disconnect the line from the spider to each injector and put a shot glass under it. Turn on the fuel pump, open the throttle and mixture (watching so you don?t overflow any shot glass), turn off the pump and see what you have.

Simple, accurate and definitive on ?spider crud? problem or not. We used this on an IO360 and sure enough we found the smoking gun. Here it the post: http://www.vansairforce.com/community/showthread.php?t=131769&highlight=Shot+glass+test
Carl

801270-F8-DF71-4-D8-E-9-E4-C-42-FC68-E2-FBAC.jpg
 
It would be very helpful to see the rest of the data (FF, CHT, etc). If CHT is also dropping when EGT drops, it is certainly a FF problem or induction leak.

Can you share a link to the flight data?
 
Anytime you suspect a spider issue, do the simple shot glass test. Disconnect the line from the spider to each injector and put a shot glass under it. Turn on the fuel pump, open the throttle and mixture (watching so you don’t overflow any shot glass), turn off the pump and see what you have.

Simple, accurate and definitive on “spider crud” problem or not. We used this on an IO360 and sure enough we found the smoking gun. Here it the post: http://www.vansairforce.com/community/showthread.php?t=131769&highlight=Shot+glass+test
Carl

Thank you. I'll be trying this as soon as I get a chance.
 
If CHT is also dropping when EGT drops, it is certainly a FF problem or induction leak.

It does. ... Usually it happens when I pull power in the pattern. #1 EGT goes up 50 degrees and then drops like a rock. CHT naturally comes down, too. In the original post I show where I was at the MAP sweet-spot for a while where #1 EGT jumped up about 50 degrees and stayed there.
 
Classic Intake leak. Most likely the gasket.

Go to altitude, say 7500, do a GAMI Lean Test. Take not of the fuel flow as each cylinder peaks.

Take note of the MAP and RPM you used at 7500'.

Descend down to say 2500' set the same MAP and RPM, then do the same GAMI lean test. If you have a leak in the intake system anywhere (and inseams like you do) the result will be obvious.
 
Classic Intake leak. Most likely the gasket.

Go to altitude, say 7500, do a GAMI Lean Test. Take not of the fuel flow as each cylinder peaks.

Take note of the MAP and RPM you used at 7500'.

Descend down to say 2500' set the same MAP and RPM, then do the same GAMI lean test. If you have a leak in the intake system anywhere (and inseams like you do) the result will be obvious.

Anything above 11” tracks the same as the other cylinders. 11” is a lot of vacuum and should display intake leak syptoms ther as well, but it does not. Mixture issues that track MAP, or indirectly fuel flow are usually from the injection system.

Strongly suggest the test that carl references.

Larry
 
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I have a question for the community here. At a certain MAP my #1 EGT goes up 50 degrees. This has happened ever since first flight. It doesn't appear to be causing me any issues. An example of when it happens is when I pull power in the pattern to start a descent. Periodically, I've tried to figure it out. I've cleaned injectors, I've searched for intake leaks, I've gapped and cleaned and eventually replaced plugs. Nothing changes the behavior. Does anyone have any ideas? And are there any opinions on what long term impact (if any) there might be on my engine. See chart below for a nice example.

Bottom trace is MAP. Top traces are EGTs. #1 is the one that stands out from the others.

egq_and_map1-1.png


You need a new engine! That chart clearly indicates your engine is going to fail. I wouldn't fly my family in that airplane! Make sure your fire extinguisher is serviceable - guaranteed engine failure within the next 5,000 hours!

Seems the main function of an engine analyzer is to confuse worry people. Most of them do a fantastic job! And it seems we're disappointed when they don't show anything normal. Ever see someone post something that said - look how normal my engine is running"?

Don't forget the first flight didn't occur with the invention of the solid state capacitor.
 
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Seems the main function of an engine analyzer is to confuse worry people.

On the contrary. It is extremely helpful in knowing the health of an engine and when things are right or not. Sites like Savvy Aviation for free data analysis are fantastic and a great learning tool. If you want, you can pay a small annual fee for professional analysis.

For anyone that wants to ensure their engine is properly tuned and running optimally, access to the flight test profile is also free to gather the appropriate data.

https://resources.savvyaviation.com/resources/other-documents/flight-test-profile/
 
Each output of the spider has a V shaped orrifice. Its main purpose is to meter fuel (technically it is to increase pressure) at and somewhat above idle. Partial blockage at the very bottom of the V would cause lean running for that cylinder only at low MAP levels. It could also account for the very slightly lean condition you are seeing at high MAPs. This is somewhat common with new spiders or fuel systems - debris from manufacturing . Even very small debris can cause this

It is easy to take apart and clean if you are competent and careful.

Larry

I have been chasing resolution of exactly the same issue as reported by the original poster.

The hardest part was plucking up the courage to open the fuel spider. Whilst nothing was visually evident, a thorough blow through followed by re-assembly, leak test, lock wire, ground run & proving flight has resolved my issue.

Grateful thanks to Larry, VAF contributors and Glenn in Sydney for their help!
 
On the contrary. It is extremely helpful in knowing the health of an engine and when things are right or not. Sites like Savvy Aviation for free data analysis are fantastic and a great learning tool. If you want, you can pay a small annual fee for professional analysis.

For anyone that wants to ensure their engine is properly tuned and running optimally, access to the flight test profile is also free to gather the appropriate data. https://resources.savvyaviation.com/resources/other-documents/flight-test-profile/
Mike of Savvy is pretty good source of solid advice. Here is him giving his background. Interesting path to his career now. https://youtu.be/l-gNZuqa_Ug

12 or 16 channel engine analyzers are amazing tools to troubleshoot or look for trends... No one doubts. However having so much data can cause concern and confusion when it is normal. Reading your engine monitors plots (OP, OT, FP, FF, MAP, EGT and CHT) is something every pilot can learn.

Interesting analyses of #1 jug EGT dropping more than other Jugs at LOW LOW power in this thread. Air leaks or some crud in the injector, line, spider is spot on. I don't think Mike could do better. Compression test? A leaky exhaust valve can cause issues at low power not found at higher power as the valve may seat better at higher power verses low.

This EGT issue would not be known in GA 20 or 30 years ago. This #1 dropping off may be normal based on the position of the #1 jug and induction system at low power. Each jug in different locations have different CHT. We all know that. They will also have different EGT, due to difference in manufacture of each jug/head and induction runners and exhaust run lengths. It is not always value added to normalize all jugs at LOW POWER....

After doing the shot glass volume test at different fuel flows/pressure and swapping jets around, the issue is the same, it is OK. Engine runs normal and balanced at higher power settings (MAP > 20 In Hg). There is no damage you can have having low EGT at low power. HOWEVER low temps means the fuel has less lead scavenging reactions built in to the fuels additives. However if low EGT is to super lean condition there is no issue.
 
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Can you clean the spider in an ultrasonic machine ?

Hi All,

Very interested by this post.

I struggled with 2 hot cylinders from new in my RV10 and despite all baffling modifications, I couldn't solve them. How could they be fouled, they were new. Then once service I decided to take the injectors out, and clean them in my home ultrasonic machine with a few drops of soap in. After 5 mins, the water was filthy and on reinstallation the engine sounded completely different, had more power than I ever had from new, and my hot cylinder problems completely disappeared.

Not sure what the problem was, debris of some sort were blocking the restrictors, from machining or running in at the factory, but something wasn't right from day 1 that is much better now.

I just wondered, if there were debris in the injectors from new, would it be worth doing a shot glass test, or just putting the spider in the ultrasonic cleaner for a whizz too? Cant do any harm and ultrasonics are great from cleaning meshes.

Best Amer
 
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