Hot EGT, help diagnose

[201er]

Last few flights #4 EGT has been running hotter/richer than the rest when cruising LOP which has been driving the CHTs undesirably high on that cylinder. It's tough to lean further because it causes power to drop off and roughness on the other cylinders. Astonishingly, the GAMI spread is still being reported as anywhere between 0.0 and 0.3gph.

 

I'm attaching a snapshot data point from my JPI830 that may illustrate the situation.

 

 

Any ideas of what's going on and how to improve it? I can share the JPI log file with anyone experienced in analyzing these.

[N201MKTurbo]

A bad spark plug,

 

With only one spark plug fireing it slows the combustion process and leaves more heat in the exhaust gases.

 

The mixture situation will not change in this sceanerio. The plug may me only misfireing at high power. Do a full power mag check the next time you are flying.

[Shadrach]

MAP? Why do you think your #4 EGT is high? I see mid 1400s at peak on some cylinders at just about any MAP above 24". Are you sure that EGT is higher, and not just CHT (which could be a baffle issue)? A failed plug [or mag] will typically generate EGTs well over 1500 because the combustion slows way down due to the single point of ignition and the burning combustion event ends up going out the exhaust. This however would not raise CHT, quite the opposite, CHT would fall.

If you haven't already, look at some old data to see if the changes in EGT are really that significant (please post it if you do). If you have a CHT issue on a single cylinder, it most likely a baffling issue. I doubt it has anything to do with spark or fuel, but I'm always open to things I have not thought of. Look forward to your reply!

[201er]

Here are two similar LOP leans to compare to from some months ago. I doubt it's a baffling issue as none of that has changed and it's been pretty tight. What is immediately noticeable is that recently 1,2,3 EGT are about even but the #4 is 30-50 degrees hotter. On the older analysis, the EGTs were more evenly spread with #4 not being hottest and #4 CHT not being hotter than #3. I'm not comparing absolute numbers but relative to each other.

 

 

[Marauder]

It may be nothing, but I don't have such a large CHT spread between my "cool" and "warm" cylinders. If you have confidence in the fuel flow, then the next logical areas to look would be spark plugs, mags, air intake or something with the cylinders.

[Shadrach]

I'm confused, are the dates accurate? Speaking to # 4 only. The older data (10/14/12) is about 1.5 minutes of information of your engine at a constant mixture setting running ~ peak EGT and 378df on the CHT (OAT, RPM and MAP not available). The newer data (3/25/13) is about 2 minutes of information of your engine being leaned from 23ROP through peak to ~15 LOP (OAT, RPM and MAP not available).

This comparison sheds little light on your problem. Also, I assume you determining leanest and richest cylinder, peaks and FF spread when you first started flying LOP, Did you slowly and carefully determine peak on each cylinder. 4 secs is hardly enough time dial in your true peak EGT.

Knowing FF is nice, but without RPM, OAT and MAP, it does not tell much

[Shadrach]

double!

[201er]

Look, the point I'm making is that the EGTs used to be more even and more recently I noticed #4 EGT to be 50 higher and CHT on #4 is higher. From my observation when leaning it seemed that #4 is running 20-40 degrees hotter/richer when LOP. For example cylinders 1-3 may be about 30LOP while #4 is 5-10LOP. I'm more familiar with things being the other way around. A clogged injector will run leaner than the others. What could cause it to run richer?

 

Shadrach, if you have the JPI software, I can just send you the files rather than occasional snapshots. They may not be an ideal comparison but they illustrate the trend that I noticed and am trying to convey.

[kmyfm20s]

You burned a valve with that blasted LOP operation, the ROP'rs are parting now:) I would do an in air mag check LOP and see what you come up with.

[orionflt]

I agree with KMY, sounds like you may have burnt a valve, do a compression check on the cylinder and see what the compressions look like, also check for blow by and the condition of your plugs.

[Shadrach]

Look, the point I'm making is that the EGTs used to be more even and more recently I noticed #4 EGT to be 50 higher and CHT on #4 is higher. From my observation when leaning it seemed that #4 is running 20-40 degrees hotter/richer when LOP. For example cylinders 1-3 may be about 30LOP while #4 is 5-10LOP. I'm more familiar with things being the other way around. A clogged injector will run leaner than the others. What could cause it to run richer?

 

Shadrach, if you have the JPI software, I can just send you the files rather than occasional snapshots. They may not be an ideal comparison but they illustrate the trend that I noticed and am trying to convey.

Mike, I'm not trying to be a smart ass. There is just no way to analyze what may be happening without seeing a comparison of the same operating regime. If CHTs are hotter across the board, then it could be ignition related. A clogged injector will either have no effect on peak EGT temp or it will lower the peak EGT temp (if fuel flow to that cylinder is severly degraded).  What a clogged injector will do is cause a larger FF spread in between EGT peaks from cyl to cyl. All I'm saying is inspect the baffling befor you do anything. It's the cheapest first step.  on a number of occasions, I have had mechanics and partners R&R the top cowling without ensuring it is properly "dressed" (read sealed against the cowl facing forward). Another time,I once found a 3"X6" piece of plastic laying on top of #3. It was either left there or ingested, but what matters is that it had a profound affect on CHT.

 

Do feel free to send me engine data files of the similar operating regimes and I'll do my best to tell you what I see!

[Marauder]

Look, the point I'm making is that the EGTs used to be more even and more recently I noticed #4 EGT to be 50 higher and CHT on #4 is higher. From my observation when leaning it seemed that #4 is running 20-40 degrees hotter/richer when LOP. For example cylinders 1-3 may be about 30LOP while #4 is 5-10LOP. I'm more familiar with things being the other way around. A clogged injector will run leaner than the others. What could cause it to run richer?

 

Shadrach, if you have the JPI software, I can just send you the files rather than occasional snapshots. They may not be an ideal comparison but they illustrate the trend that I noticed and am trying to convey.

 

 

Mike -- based on what you are seeing now versus what you were seeing, it is clear that something changed. As was pointed out by others, there can be a number of root causes. If this were my plane, I would do another leaned flight to air check the mags and record data. If the mags come back okay, I would have a compression test done and go from there.

 

When I saw your data, I pulled mine this morning from a couple of flights over the summer. Unfortuantely, I left the stupid flash drive with the data at home. But what I saw was a consistent trend. Note the word "trend". My absolute temps varied because of the different air temps I flew in, but they stayed consistent across each other.

 

As I mentioned earlier, my CHT temps are a lot closer (like within 20 degrees of each other). I think you have some investigation work ahead.

[N201MKTurbo]

Life was so much simpler before engine scanners. You just went out and flew the plane. If the engine ran rough you fixed it.

Now look at all the stuff you have to worry about....

[201er]

I just remembered, and this could be important, that this started since the last oil change. So it could be a baffling issue from a misplaced cowling or it could have something to do with the mag timing being reset to 25BTDC. Plugs weren't removed this time around. Does the timing or oil change say anything?

[Marauder]

I just remembered, and this could be important, that this started since the last oil change. So it could be a baffling issue from a misplaced cowling or it could have something to do with the mag timing being reset to 25BTDC. Plugs weren't removed this time around. Does the timing or oil change say anything?

 

 

Hmmm... what else was done during that last maintenance? I would pull the cowl and look things over. Won't be the first time a rag was left behind in a bad spot.

[kmyfm20s]

I just remembered, and this could be important, that this started since the last oil change. So it could be a baffling issue from a misplaced cowling or it could have something to do with the mag timing being reset to 25BTDC. Plugs weren't removed this time around. Does the timing or oil change say anything?

I would still do an in flight LOP mag check to rule out electrical. Why did you have the timing checked? Was it running improperly or just due?

[201er]

It has been progressively creeping forward and was checked at 23 last oil change. I let it stay there to take advantage of cooling for the summer. By now it must have been 23 or less so I had them bring it back to 25. I think some power has been restored and running well LOP except for this hotter cylinder issue.

 

For an in flight mag check... is it same as on the ground just at cruise power?

[Shadrach]

Hi Mike,

I replied to your email. Timing plays a key roll in peak cylinder pressure, the angle at which it occurs and the heat generated. Byron would be a good person to ring in here as I seem to remember that he went through the process of advancing from 20BTDC to 25BTDC; I can speak thoretically about it, but he has real world data. As I said in my email for the purposes of this discussion, all other things being equal, advancing the timing will cause an increase in CHT!

[Marauder]

 

For an in flight mag check... is it same as on the ground just at cruise power?

 

Yes. Your JPI will pick up any issues.

[Shadrach]

It has been progressively creeping forward and was checked at 23 last oil change. I let it stay there to take advantage of cooling for the summer. By now it must have been 23 or less so I had them bring it back to 25. I think some power has been restored and running well LOP except for this hotter cylinder issue.

 

For an in flight mag check... is it same as on the ground just at cruise power?

Yes it's fine to do a cruise power mag check. High power LOP is the most strenuous check of the ignition system. However, the only way a mag malfuntion would increase CHT is if it was firing in advance of spec.  As I said earlier, if you lose a mag or a spark plug in flight, EGTs go up, but CHTs go down... That is not your issue.

[Shadrach]

Yes. Your JPI will pick up any issues.

If he does an inflight mag check and has a mag issue, his butt will likey notice the issue long before he reads it off the JPI...  

[201er]

So firewall the throttle and prop and go 70LOP on 11GPH (about 85% power) and then do a mag check with JPI in normalize to check EGT rise across all cylinders?

[Shadrach]

EGT rise is not going to tell you much on a mag check...just make sure they do rise (It should be pretty dramatic)!

 

If your engine runs smooth (or relatively so) at that power setting on each mag, I'd say your Mags are fine. If it runs a bit rough, enrichen a bit. If it runs smooth on one mag at just about any High power LOP setting, then your mags are strong... 

 

As I said before, I don't think this is mag performance related...I think it is likely mag setting related and could be the some of a number of little things that happened the last time your MX was in there.

[kmyfm20s]

Here is a good webinar on mags by Mike Busch. He talks about the mag check and don't worry about the length of the video it has a lot of Q&A at the end.

http://www.eaavideo.org/video.aspx?v=1367499350001

[kmyfm20s]

By doing it you will isolate whether it is a Mag, spark plug, or cylinder issue.