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Posted

Oh. Who cares about EGT?

I agree that CHT is what we are trying control for the longevity of the engine, but EGTs can tell us a lot about fuel distribution, ignition, and valve health.

  • Like 1
Posted

There could be some confusion...

For the most part, the absolute value of EGT heavily depends on a couple of variables including position in the exhaust system, including...

- depth into the exhaust stream.

- distance from the exhaust valve.

- location regarding three into one pipes, including more than one cylinder in the reading.

There is not much comparative info to be gained from one EGT reading. As in, you won't be able to compare to other planes...

But everyone benefits by using the EGT for degrees ROP or LOP when setting the mixture.

Of course, if you use the lean til rough, then enrich til smooth method, you don't need an EGT.

To answer the question of 'who cares about EGT'...

- Anyone that sets mixture with precision using degrees ROP or LOP...

- Anyone that is using their engine monitor to check FF differences for each cylinder. AKA Gami Spread...

- Anyone that has foreign material lodged in a fuel injector...

What is probably missing from the post regarding 'who cares...' Is the

Posted

Oh. Who cares about EGT?

 

 

I do if it changes in a way that demonstrates an issue.  Higher than typically attainable EGTs usually indicate an ignition issue (except for Super Dave's super mystery). Oscillating EGTs can indicate that an exhaust valve is failing. EGTs can reveal a clogged injector, mag problem, failed or failing spark plug etc... I care about EGTs!  I just don't care much about the actual number accept for under specific circumstances.

Posted

Just another thought - do you have double (or even triple) valve springs on that engine? If one has broken that you might be getting 'valve bounce' which would give you a high EGT

  • Like 1
Posted

Just another thought - do you have double (or even triple) valve springs on that engine? If one has broken that you might be getting 'valve bounce' which would give you a high EGT

That's a good one. I spoke with a couple of different tech. reps. from Lycoming today and while he thought it was unlikely, one of the reps. sugested taking a look at that very thing. Our cylinders have double valve springs.

Posted

How did I do Harley?

Best regards,

-a-

 

Ross (Shadrach) said it better  ;)

 

At the end of the day, you want your EGT's to be well behaved. 

 

What does that mean?

 

All moving together, like a delicate dance.

 

Keep your eye though, on the CHTs.

 

Here's EGTs (top) dancing delicately, with CHT's behaving badly:

 

post-7222-0-67295900-1429069209_thumb.jp

  • Like 2
Posted

Hello to all and thanks for your input on this issue. I'm one of the other owners of Super Dave's super mystery Mooney. I'm also an A&P/IA Still hoping we can get to the bottom of this issue as I for one am totally stumped!

 

To rule out a possible injector issue, I swapped the injectors between the #2 and #4 cylinder and still no change. I've also flow checked all 4 fuel injector nozzles for 60 seconds. I had the external power hooked up, had mixture and power levers full forward and our JPI was reading about 6GPH during my test. All four injectors measured out approximately 150cc's of fuel during this test so I think it's safe to say that it's not an injector.

 

As Dave mentioned, we swapped the #2 EGT probe between cylinders #2 and #4 in every such combinations that I can confirm the probe is working correctly.

 

I have borescoped both #2 and #4 cylinders and other than #2 appearing a little more wet than #4, I don't see any issues. I don't recall seeing any scoring to the cylinder wall and the cross hatching is still visible as well. However I did notice some oil in the bottom of the #2 intake tube and there some deposits near the exhaust valve on the #2 cylinder. More-so than the #4 cylinder. Is it possible that the #2 cylinder intake valve guide is worn enough where air is getting through it? I know it's a stretch but at this point we've ruled out all the obvious causes of our issue.

 

Just last night I put a new intake gasket between the cylinder head flange and the #2 intake tube and still no change. I was going to change out the lower orange o-ring on the #2 intake tube but it's impossible without removing the entire exhaust first. There don't appear to be any cuts, nicks or flat spots on the o-ring so I think it's okay.

 

I have most of these borescope videos saved to my Google Drive account and would gladly share them if you would like to take a look. Today I plan on downloading the JPI and graphing out the flight where the issue first happened in hopes that it might show us something but at this point I'm not sure what to do next other than opening the rocker box on the #2 cylinder and taking a look. I'll share the JPI data later too if you think it might help. Thanks in advance!

 

-Frustrated Mooney Mechanic

Posted

If there is no CHT increase I would suspect an instrumentation problem. Some EGT monitors are sensitive to ground connections. High DC current from the alternator can induce voltage on a poor ground connection that can affect the EGT reading of all the probes. Check engine ground straps connections to the airframe. Also EGT monitor ground connections.

José

Posted

If there is no CHT increase I would suspect an instrumentation problem. Some EGT monitors are sensitive to ground connections. High DC current from the alternator can induce voltage on a poor ground connection that can affect the EGT reading of all the probes. Check engine ground straps connections to the airframe. Also EGT monitor ground connections.José

Probes have been swapped to rule this out.

Anyway... To expand on Kyle's update: Lycoming told us not to worry about the high EGT. As long as other paramaters are normal, just keep running it without further investigation... Not exactly reassuring.

I have one more half baked theory. When Kyle swapped the injectors, he stuck a borescope into the injector hole and saw some oil residue, sugesting that some oil being sucked down the intake valve guide. My theory is that the oil is mixing with the fuel and air, and is slowing combustion down a little bit so that we are seeing an elevated EGT. Similar to the way that retarding ignition raises EGT, or turning off a spark plug during a mag check raises EGT.

Anyone buy it?

Posted

Dave swapping probes will not help on this problem. It looks like an engine or EGT indicator ground connection problem.

José

Why would that effect only 1 cylinder? Other EGTs are fine as well as the CHTs. I would expect the voltage readout to be could be affected as well.
Posted

As promised, here's the JPI data from the flight where the issue first began happening. I've got to agree with teejayevans on this one. The JPI data is supporting evidence that something happened. The question still remains as to what exactly it is that happened though.

 

Posted

I have one more half baked theory. When Kyle swapped the injectors, he stuck a borescope into the injector hole and saw some oil residue, sugesting that some oil being sucked down the intake valve guide. My theory is that the oil is mixing with the fuel and air, and is slowing combustion down a little bit so that we are seeing an elevated EGT. Similar to the way that retarding ignition raises EGT, or turning off a spark plug during a mag check raises EGT.

Anyone buy it?

 

I would sort of buy it, but think you would have seen a noticeable increase in oil consumption, particularly if something has 'broken' (as suggested by the JPI data) to change it that significantly.  Have you whipped a rocker cover off to check the springs, and whilst you are at it, ensure some rocker/valve clearance exists? Whilst you are there, you can try the 'wobble test' on the inlet to see if the guides are failing. I'm not sure of the symptoms of a massively oversize clearance (other than the noise on most engines) but guess if you are compressing the spent charge on the start of the exhaust stroke the temperature is going to rise

 

Welcome to the fray Kyle!

Posted

As promised, here's the JPI data from the flight where the issue first began happening. I've got to agree with teejayevans on this one. The JPI data is supporting evidence that something happened. The question still remains as to what exactly it is that happened though.

 

those images are too low resolution to interpret. Sign on to Savvy Aviators free service and upload the complete set of JPI data (multiple flights from this one on.....   https://www.savvyanalysis.com/home

You can then put the shared link to those files here so we can look at them in detail.

You are right, about two-thirds through the flight it looks like some event occurred that reduced all the values but the one EGT. 

  • Like 1
Posted

As promised, here's the JPI data from the flight where the issue first began happening. I've got to agree with teejayevans on this one. The JPI data is supporting evidence that something happened. The question still remains as to what exactly it is that happened though.

What exactly did you do about 2/3 that cause the CHTs and 3 of the EGTs to drop? The 1 EGT doesn't rise so much as it stays high. It's hard to tell from low res pix
Posted

I would sort of buy it, but think you would have seen a noticeable increase in oil consumption, particularly if something has 'broken' (as suggested by the JPI data) to change it that significantly.  Have you whipped a rocker cover off to check the springs, and whilst you are at it, ensure some rocker/valve clearance exists? Whilst you are there, you can try the 'wobble test' on the inlet to see if the guides are failing. I'm not sure of the symptoms of a massively oversize clearance (other than the noise on most engines) but guess if you are compressing the spent charge on the start of the exhaust stroke the temperature is going to rise

 

Welcome to the fray Kyle!

 

Opening the rocker cover and taking a peek is the only thing we haven't looked at yet. Hopefully we can get at it this week and come to a conclusion with this frustrating ordeal. Thanks for the input!

Posted

Here's the link to the Savvy Analysis page. Let me know if it doesn't work as I'm fairly new to this download data.

 

First indication of high #2 EGT

https://www.savvyanalysis.com/flight/909290/0b7cfa44-4d8a-4fc1-8b1d-e351520276c0

Following flight

https://www.savvyanalysis.com/flight/909291/4081b956-abf9-4d21-8494-3e2b15460c1f

Following flight

https://www.savvyanalysis.com/flight/909292/2f5606ab-6aa6-4ba7-86b6-e8b56aff3df6

Posted

Probes have been swapped to rule this out.

Anyone buy it?

I like the way you think, but no, I'm not buying it. So, The probes have been switched out but what about the wires?  Do you have enough slack to swap  2 and 4?

Posted

I like the way you think, but no, I'm not buying it. So, The probes have been switched out but what about the wires?  Do you have enough slack to swap  2 and 4?

 

That I did. I physically did the labor and flew both of these flights so I can confirm that it's not a probe. =/

 

Here's the flight where we physically swapped the #2 and #4 probes but left the leads the same (#2 on the JPI still read #2 cylinder)

https://www.savvyanalysis.com/flight/909301/a0e24670-c5cb-404a-8acf-1dbfaf61f84b

 

And here's the flight afterwards where I left the probes hooked up to their respective channels (#4 on the JPI would be reading the #2 cylinder and vice versa)

https://www.savvyanalysis.com/flight/909302/30752cab-4741-417b-8da1-30353819efb9

Posted

Here's the link to the Savvy Analysis page. Let me know if it doesn't work as I'm fairly new to this download data.

 

First indication of high #2 EGT

https://www.savvyanalysis.com/flight/909290/0b7cfa44-4d8a-4fc1-8b1d-e351520276c0

Following flight

https://www.savvyanalysis.com/flight/909291/4081b956-abf9-4d21-8494-3e2b15460c1f

Following flight

https://www.savvyanalysis.com/flight/909292/2f5606ab-6aa6-4ba7-86b6-e8b56aff3df6

This is perfect. I looked at all three files. 

One of the posts stated the EGT was now over 1600°F ? I only saw mid 1400s. Regardless, your problem is related to fuel flow. In each of the flights you can see the EGT and CHT react to the changes in FF. To see this clearly, click on the box in the upper right corner and a pull down menu will appear, click on the FF and it overlays fuel flow to the EGT graph. You will see the first event occurred at :59 minutes into the flight but recovered about 10 minutes later. The second event occurred at 2:15:36 but the FF stayed higher and the EGT did not drop as the other cylinders did. 

There is a fuel distribution problem. 

Posted

This is perfect. I looked at all three files. 

One of the posts stated the EGT was now over 1600°F ? I only saw mid 1400s. Regardless, your problem is related to fuel flow. In each of the flights you can see the EGT and CHT react to the changes in FF. To see this clearly, click on the box in the upper right corner and a pull down menu will appear, click on the FF and it overlays fuel flow to the EGT graph. You will see the first event occurred at :59 minutes into the flight but recovered about 10 minutes later. The second event occurred at 2:15:36 but the FF stayed higher and the EGT did not drop as the other cylinders did. 

There is a fuel distribution problem. 

 

I would be inclined to agree with you on a fuel distribution problem. Considering the probe troubleshooting, new gasket on the #2 intake tube and compression check of 78/80 I'd have to say its a fuel nozzle. However, we swapped the nozzles between #2 and #4 with no change so next I'd be inclined to think it's in our fuel manifold/distribution tubes or perhaps something to do with the fuel injector itsef? I haven't pulled the fuel injector screen since last annual but it might be next on our list of things to check along with pulling the rocker cover and checking for a damaged spring/loose valve. Any other thoughts/suggestions?

Posted

That I'm not sure about. That particular flight took place when a different owner was flying. Are you talking about the two spikes/dips at 00:28 and 1:03 marks?

Posted

This is perfect. I looked at all three files. 

One of the posts stated the EGT was now over 1600°F ? I only saw mid 1400s. Regardless, your problem is related to fuel flow. In each of the flights you can see the EGT and CHT react to the changes in FF. To see this clearly, click on the box in the upper right corner and a pull down menu will appear, click on the FF and it overlays fuel flow to the EGT graph. You will see the first event occurred at :59 minutes into the flight but recovered about 10 minutes later. The second event occurred at 2:15:36 but the FF stayed higher and the EGT did not drop as the other cylinders did. 

There is a fuel distribution problem. 

 

This is perfect. I looked at all three files. 

One of the posts stated the EGT was now over 1600°F ? I only saw mid 1400s. Regardless, your problem is related to fuel flow. In each of the flights you can see the EGT and CHT react to the changes in FF. To see this clearly, click on the box in the upper right corner and a pull down menu will appear, click on the FF and it overlays fuel flow to the EGT graph. You will see the first event occurred at :59 minutes into the flight but recovered about 10 minutes later. The second event occurred at 2:15:36 but the FF stayed higher and the EGT did not drop as the other cylinders did. 

There is a fuel distribution problem. 

 

Yes, peak EGT is now over 1600º. Maybe Kyle can post some of the trouble shooting flights (thanks Kyle) where we did the induction leak test and LOP inflight mag checks.

 

The three flights you referred to were flown by our other partner on his way from FL to WI. He typicly cruises WOT 100º ROP. The first event at :59 is i think, just a climb. There doesn't look to be a divergence of #2 EGT at that point. At around 2:15 It looks like he noticed something amiss and reduced power and enriched mixture. Then, after looking things over for a couple of minutes, left mixture full rich and went back to full power. In an effort to keep #2 EGT where he was used to seeing it, poor Scott flew the rest of the way home 200º ROP, burning fuel like an Ovation at F model speeds.

 

I still don't buy that this is a fuel distribution issue. How would fuel distribution cause a cylinder that has always peaked in the high 1400ºs - low 1500ºs to now peak at 1600º+. Also, I don't understand how an engine with poor fuel distribution still has a Gami spread of .2-.3 GPH.

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