One cylinder running warm

[Skylane81E]

Thermocouple or ignition.

Swap probes and see if it follows the probe, if so replace bad probe and move on. If not clean plugs, and REALLY check out the ignition leads going to the suspect cylinder.

If you were idling OK I'd lean against an induction leak as they usually show most at low MP. However I wouldn't take it off the table either.

 

[jsstevens]

I'm really not shy about exhibiting my ignorance in the pursuit of knowledge, so:

If the CHT is normal or low and the EGT is high, isn't that an indicator of still burning gasses in the exhaust? Would an exhaust valve leak cause that?

John (Standing by to be educated, but preferably not ridiculed...)

 

[Skylane81E]

A leaky valve is a possibility but other things can cause it too so I start with the cheap/easy things first before loading the parts cannon with money and shooting it at the airplane.

 

[azure]

A CHT of 340 is also low. Remember, the limit on Lycoming cylinders is 475-500 (depending on the cylinder). I aim to keep below 380 (that's the goal I recommend), and on the Aztec that is exactly where the hottest cylinders are running at all times. At 340 and below, you are not only below the limit, you're below the goal. I wouldn't worry about it.

Thanks Ted. I'm not worried about the CHT itself, but about why it and the EGT on #2 stayed high for at least 2 minutes after pulling the throttle back to idle. and didn't correct itself until we did another full power run-up.

If it makes a difference (just trying to throw out as much info as possible), my A&P fixed an induction leak in #2 this spring. The only thing unusual about #2 recently is that it's been the coolest running cylinder of the four (both EGT and CHT), and now this... just seems strange.

I'd suspect an induction leak, a partially-fouled plug (this would be my biggest guess), or potentially a clogged nozzle or some other issue with your fuel system.

I mentioned the plug idea to him last night, and he said it "shouldn't" be that, which I'm guessing means that it shouldn't because he just checked the plugs a couple of weeks ago. But I didn't press any further.

 

[Skylane81E]

Plugs can foul on the first start. If he hasn't checked them as part of the hunt for this issue I'd be enclined to ask that they be looked at again

 

[azure]

I think by "welded" the sensor locations are fixed (welded) on the exhaust headers - the sensors i would guess are threaded in or otherwise attached to these points.

I'm really not sure what he meant by "welded" (actually it was "unwelded" in reference to moving the sensor locations). He explained last night that the sensor are clamped on and the probes run through a tiny hole in the exhaust header so they sample the exhaust inside the tube. I think he meant that to move them, he'd have to seal that hole and drill one somewhere else.

The difference in readings you are talking about is something like three or four percent. If everything is running smoothly, your A&P is not alarmed, and your readings stay consistent... just fly it.

The engine feels and sounds smooth, but the readings aren't consistent, that's the problem. #1 went from 1330 leaned to 12 gph on the way to 57D, to 1390 at about 16 gph (almost full rich at 24 squared) on the way back. I really don't want to fly it again until I have some idea what's going on with it.

 

[azure]

I'm really not shy about exhibiting my ignorance in the pursuit of knowledge, so:

If the CHT is normal or low and the EGT is high, isn't that an indicator of still burning gasses in the exhaust? Would an exhaust valve leak cause that?

John (Standing by to be educated, but preferably not ridiculed...)

I'm a little shier about exhibiting my ignorance... but yes this was one of my first thoughts, that fuel is igniting in the exhaust. I really hope it's not a leaky valve, but my gut feeling is that it probably is.

 

[azure]

Plugs can foul on the first start. If he hasn't checked them as part of the hunt for this issue I'd be enclined to ask that they be looked at again

Wouldn't a single fouled plug show up as roughness, and then during the mag check as an uneven RPM drop?

 

[Skylane81E]

Things that cause high single cylinder egt:
poor ignition
poor mixture
exhaust leak
and
bad insrumentation.

Rank each item by the cost to check and start with the cheapest and move to the more expensive.

 

[azure]

Though I have to say that from the start I've leaned toward something maintenance-induced... since I had nothing weird going on with either #1 or #2 until he (a) fixed an induction leak in #4 and (b) rotated (re-oriented) the injectors.

The only symptoms before that were the large RPM drops on mag check in warm temperatures, the "morning sickness" which seems to only happen when the engine is preheated, and the one time engine stoppage during idle check that hasn't happened since.

 

[Skylane81E]

Wouldn't a single fouled plug show up as roughness, and then during the mag check as an uneven RPM drop?

Roughness no, I could pull the lead off a plug and you wouldn't know it untill the mag check.

An d yes the mag check should be uneven but that doesn't mean that its uneven enough to notice.

Also leads, a n intermittent short or open in an ignition lead can cause your symptoms

 

[azure]

The latest news: my A&P found that injector #1 was partially clogged. I believe he said the flow test was an ounce short compared with two pints through the others, which is about 3% slow. It's very hard for me to believe that tiny difference could cause the difference in EGTs, but he's soaking it now and hopes to have it cleaned out and ready to test again sometime tonight.

Of course, since he didn't actually see the blockage, it's possible that it's something that can move or deform under pressure and occlude less or more fuel flow at different times.

Oh yeah. For my peace of mind, he's also going to compression check the cylinder to rule out a leaky exhaust valve.

 

[bbchien]

The latest news: my A&P found that injector #1 was partially clogged. I believe he said the flow test was an ounce short compared with two pints through the others, which is about 3% slow.

Liz, From the point of view of ROP/LOP, that's quite a lot, actually, esp when near peak stoichiometry.....

It's very hard for me to believe that tiny difference could cause the difference in EGTs, but he's soaking it now and hopes to have it cleaned out and ready to test again sometime tonight.

Of course, since he didn't actually see the blockage, it's possible that it's something that can move or deform under pressure and occlude less or more fuel flow at different times.

Oh yeah. For my peace of mind, he's also going to compression check the cylinder to rule out a leaky exhaust valve.

Yup

 

[gismo]

Back at VLL I did a straight-in and hailed my A&P, who happened to be working late. We did a full-power runup and verified what I had seen in the air, then leaned out to find where the different cylinders would peak, under his direction. #2 peaked first at about 1470, but #1 ws still rising and peaked at 1520, the highest EGT I've seen on ANY cylinder since buying the plane (though Tom recorded EGTs like that during the first few hours of break-in).

{Edit: changed #2 to #1 in the first sentence}
If #1 peaked last as you leaned, that means it is the richest cylinder (first to peak is the leanest because it hits the peak at the highest fuel flow). So if #1 peaked last there's no way it's injector was partially clogged so any attempts at cleaning aren't likely to improve anything.

Strangely, #2's EGT stayed about 150 above the others even after bringing the throttle back to idle, and even its CHT stayed up around 340 -- the highest CHT I saw today. We did a second full-power runup without leaning, which caused the #2 CHT to settle into the high 200s. After pulling the power back again, all the EGTs and CHTs came back down to normal idle levels.

EGTs at idle are relatively unimportant and often very inconsistent. EGTs also may take a long time (upwards of a minute) to settle down at low power and they are likely to change significantly with small changes in RPM.

Things my A&P is planning to check:

1. Possible problems with the JPI EGT probes - he wants to swap 1 and 2 with 3 and 4 to see if the high readings follow the probes. But does that make sense in view of the high CHT on #2? My gut feeling is no -- something real is/was definitely going on with at least that cylinder.

Since Cyl 2 peaked first when leaning at cruise power it is the leanest cylinder and that would/could make the CHT higher if you're running ROP. (LOP it would be the other way around). Typically this isn't much of an issue in cruise if you're running 100+ ROP on the leanest cylinder (first to peak rich to lean) unless the leanest cylinder is getting a lot less fuel than the others and in any case if you set the cruise mixture at least 100F ROP on that leanest jug.

2. Possible intermittent induction leak(s) due to slipping O-rings, or even a cracked flange.

One thing to remember is that on a NA engine small induction leaks have almost no effect when the throttle is wide open as is typically the case when cruising at altitude and when climbing because there is almost no pressure difference between ambient and manifold pressure (the airflow through the leak is proportional to the pressure difference). Typical symptoms of an induction leak are rough idle and a significant change in mixture distribution between WOT at altitude and partial throttle producing the same power at a lower altitude. There is a variation of the GAMI lean test (published on their website) that will give a pretty clear indication if you have much of an induction leak.

I'm really concerned that both of those cylinders might have been running in the "red box", especially #1 during flight but also #2 during the runup, and I wonder if the persistently high CHT on #2 might be an indication of detonation.

First of all, the power level during runnup is so low (<50%) that there is no "red box" and you can safely run with any mixture as long as you don't let the CHTs go too high (i.e. >400F) due to the lack of cooling.
Second, as I mentioned, if you set the ROP mixture using the first cylinder to peak as your reference you won't be in red territory as long as that cylinder is sufficiently ROP during full power and cruise. Also there's a big difference in the size of the "red box" depending on your power level. Below 60% any mixture is safe (again as long as you keep CHTs under control, preferably <380F). At 65% you should avoid continuous (more than a few minutes) from 50F ROP to peak (25 ROP is the center of the red zone). At 70% you should be at least 100 ROP (or 30-50 LOP) and at 75% I'd stay at least 125F ROP or more than 50 LOP. Above 75% you need to be a lot richer, typically 200-250 ROP at full power. Keep in mind you can only produce full power when the DA is close to sea level.

As to the "welded" EGT probe question, I've NEVER seen EGT probes that were deliberately welded into the exhaust on any certificated aircraft. I have seen a couple where the probes were so corroded they were difficult to remove without destroying them and I might have referred to such an example as having the probes "welded in".

I've also never seen a situation where a problem with a probe caused a significantly high reading (i.e. more than 50-100F high). Generally probe problems result in intermittent or continuous low or nonexistent readings. An abnormally high EGT reading at all mixtures is almost always caused by one of four things: Probe too close to cylinder, retarded timing, or exhaust valve leak.

 

[azure]

Lance, forgive me for not reading the rest of your post before replying, but #2 didn't peak last... it actually peaked first, and at a much lower temperature than #1. That is actually very different from before, when #3 peaked first. I really don't know what to make of that, and neither does my A&P.

He reported this morning that he's in the process of replacing all the injector gaskets since he's suspicious of several of them.

 

[gismo]

Lance, forgive me for not reading the rest of your post before replying, but #2 didn't peak last... it actually peaked first, and at a much lower temperature than #1. That is actually very different from before, when #3 peaked first. I really don't know what to make of that, and neither does my A&P.

My bad. I wrote #2 but meant #1. Your post I was quoting said that #2 peaked first and #1 peaked at a lower fuel flow. I was trying to say that this would mean that the #1 injector was passing more fuel or at least that the #1 cylinder was running richer than #2 and cleaning the #1 injector wasn't going to help anything.

He reported this morning that he's in the process of replacing all the injector gaskets since he's suspicious of several of them.

I don't know what an "injector gasket" is unless you're talking about something inside the injectors (you're not supposed to disassemble them in the field). I haven't looked at a Lycoming IO360 in a while but I believe they use an injector very similar to what's used on the Continental engines which has a tapered pipe thread on the cylinder side and a compression fitting on the end that connects to the fuel servo. Perhaps the mechanic was referring to the compression fitting ferrules although any kind of leak there would dump fuel outside the injector/cylinder and leave pretty obvious stains. And a small leak of that sort wouldn't affect mixture to the cylinder enough to notice AFaIK.

 

[azure]

{Edit: changed #2 to #1 in the first sentence}
If #1 peaked last as you leaned, that means it is the richest cylinder (first to peak is the leanest because it hits the peak at the highest fuel flow). So if #1 peaked last there's no way it's injector was partially clogged so any attempts at cleaning aren't likely to improve anything.

Okay, now I understand what you're saying, and yes that makes sense. But I was talking only about the full power runup we did on the ground after I landed -- and for the last couple of weeks, in cruise, #1 was actually the first to peak, which was a change from earlier (before the last maintenance which included rotating the injectors) when #3 was always the first to peak. (Though I don't know which cylinder would have peaked first on that last flight home from 57D, since I was afraid to lean it at all.)

And there's the fact that my mechanic did measure a lower flow rate in #1 than in the others -- so I think I have to accept that it was partially clogged, though it's not clear that that was the only problem, or that it was responsible for what we saw in the runup Tuesday night.

Since Cyl 2 peaked first when leaning at cruise power it is the leanest cylinder and that would/could make the CHT higher if you're running ROP. (LOP it would be the other way around). Typically this isn't much of an issue in cruise if you're running 100+ ROP on the leanest cylinder (first to peak rich to lean) unless the leanest cylinder is getting a lot less fuel than the others and in any case if you set the cruise mixture at least 100F ROP on that leanest jug.

And that's the way I've been leaning the engine: find the peak EGT of the cylinder that peaks first, then go >~ 100F rich on that cylinder. But... #2 has NEVER before peaked first, so if it is now the leanest cylinder then something has changed. Could the conditions of the test have affected the results? This happened on the ground, and btw it was not at cruise power but at FULL power, literally WOT. And after pulling the power back to idle, its EGT and CHT stayed high for at least a couple of minutes and didn't come down until we ran the power up again. I've never seen it do that in flight, and wonder to what extent the lack of air cooling affected these results.

First of all, the power level during runnup is so low (<50%) that there is no "red box" and you can safely run with any mixture as long as you don't let the CHTs go too high (i.e. >400F) due to the lack of cooling.
Second, as I mentioned, if you set the ROP mixture using the first cylinder to peak as your reference you won't be in red territory as long as that cylinder is sufficiently ROP during full power and cruise. Also there's a big difference in the size of the "red box" depending on your power level. Below 60% any mixture is safe (again as long as you keep CHTs under control, preferably <380F). At 65% you should avoid continuous (more than a few minutes) from 50F ROP to peak (25 ROP is the center of the red zone). At 70% you should be at least 100 ROP (or 30-50 LOP) and at 75% I'd stay at least 125F ROP or more than 50 LOP. Above 75% you need to be a lot richer, typically 200-250 ROP at full power. Keep in mind you can only produce full power when the DA is close to sea level.

Yep, I know. Again, this was not a normal runup, but a full power runup during which my A&P had me go WOT and then lean the engine slo-o-o-owly to find which cylinder peaked first, then further into LOP of that cylinder and the others until the last cylinder peaked. I've never treated that engine like that before. Am I wrong in thinking that treating the engine in that manner would have put all of the cylinders into the "red box" and kept them there until we either pushed in the red knob or brought the throttle back? If I recall Deakin's graph correctly, at that power the "red box" danger zone extends all the way from about 125F ROP to something like 25 LOP (not sure about the exact value there).

And flying back from 57D Tuesday night, running at 24 squared (just under 75% power) at a full rich or nearly full rich mixture setting, the EGT on #1 was 1370-1400 the whole way. I didn't try leaning it to find how far ROP that was, but if it would have peaked anywhere near where it normally does in flight (1430-1470), I'd think that (30-100 ROP) was in the red box too.

As to the "welded" EGT probe question, I've NEVER seen EGT probes that were deliberately welded into the exhaust on any certificated aircraft. I have seen a couple where the probes were so corroded they were difficult to remove without destroying them and I might have referred to such an example as having the probes "welded in".

As I wrote earlier, I don't think he meant literally welded -- he explained that the probe was passed through a hole drilled in the exhaust tube and held firm with a clamp. The difficulty in moving the probes seems to be in sealing that hole and drilling another one.

An abnormally high EGT reading at all mixtures is almost always caused by one of four things: Probe too close to cylinder, retarded timing, or exhaust valve leak.

That's three things, did you mean three or is there a fourth? Given that my mechanic has checked the timing repeatedly, if those are the only three then that means an exhaust valve leak is really the only possibility left.

 

[gismo]

Okay, now I understand what you're saying, and yes that makes sense. But I was talking only about the full power runup we did on the ground after I landed -- and for the last couple of weeks, in cruise, #1 was actually the first to peak, which was a change from earlier (before the last maintenance which included rotating the injectors) when #3 was always the first to peak. (Though I don't know which cylinder would have peaked first on that last flight home from 57D, since I was afraid to lean it at all.)

And there's the fact that my mechanic did measure a lower flow rate in #1 than in the others -- so I think I have to accept that it was partially clogged, though it's not clear that that was the only problem, or that it was responsible for what we saw in the runup Tuesday night.

Out of the box, Continental's injector flow rates vary more than +/-5%. From what I've heard Lycoming injectors are a little better but I think it's quite possible that you one of your higher flow rate injectors used to be at the cyl 1 location and it got swapped for one of the lowest flowing injectors. The difference could be at least partially the result of some contamination but 30 minutes soaking in Hoppes #9 should clear that up. There's no reason you couldn't swap the injector in #1 with a cylinder that's running a bit richer if the soaking doesn't help.

And that's the way I've been leaning the engine: find the peak EGT of the cylinder that peaks first, then go >~ 100F rich on that cylinder. But... #2 has NEVER before peaked first, so if it is now the leanest cylinder then something has changed. Could the conditions of the test have affected the results? This happened on the ground, and btw it was not at cruise power but at FULL power, literally WOT. And after pulling the power back to idle, its EGT and CHT stayed high for at least a couple of minutes and didn't come down until we ran the power up again. I've never seen it do that in flight, and wonder to what extent the lack of air cooling affected these results.


Yep, I know. Again, this was not a normal runup, but a full power runup during which my A&P had me go WOT and then lean the engine slo-o-o-owly to find which cylinder peaked first, then further into LOP of that cylinder and the others until the last cylinder peaked. I've never treated that engine like that before. Am I wrong in thinking that treating the engine in that manner would have put all of the cylinders into the "red box" and kept them there until we either pushed in the red knob or brought the throttle back? If I recall Deakin's graph correctly, at that power the "red box" danger zone extends all the way from about 125F ROP to something like 25 LOP (not sure about the exact value there).

Which cylinder peaks first can be affected by throttle position and RPM. In any case I wouldn't repeat that full power peak testing, it may well be possible to induce detonation, especially if the CHT gets high. The external indications of detonation are a rise in CHT and a slight drop in EGT but since the cylinders are going to overheat at full power while sitting still (especially with less than full rich mixture) it won't be easy to detect a detonation event until things get way out of hand. Mild detonation by itself isn't supposed to be terribly damaging but it can easily lead to pre-ignition which can destroy the innards of a cylinder in seconds. Here's an image of the nominal "red box". You'll see that at full power (left side of the graph) the mixture needs to be well away from peak, more like 200-250 ROP or at least 50 LOP. Keep in mind that this graph is a simplified approximation and that the edges are not "sharp". Also the scale on the bottom is altitude but you can translate that to % HP by assuming that the power drops 10% for about every 1800 ft of altitude.

http://csobeech.com/images/RedBox-Mixture.gif

And flying back from 57D Tuesday night, running at 24 squared (just under 75% power) at a full rich or nearly full rich mixture setting, the EGT on #1 was 1370-1400 the whole way. I didn't try leaning it to find how far ROP that was, but if it would have peaked anywhere near where it normally does in flight (1430-1470), I'd think that (30-100 ROP) was in the red box too.

At 75% there's no concern about finding peak as long as you don't take forever. I would have checked that just to see if the peak temp was elevated by a similar amount as the full rich EGT. If I was concerned about detonation and/or if the CHTs were getting uncomfortably hot, I'd just reduce power a bit and then check for the delta from peak EGT.

Absolute full rich EGTs vary with intake air density (high density cold air at the same pressure altitude will usually make EGTs hotter).

As I wrote earlier, I don't think he meant literally welded -- he explained that the probe was passed through a hole drilled in the exhaust tube and held firm with a clamp. The difficulty in moving the probes seems to be in sealing that hole and drilling another one.

How close are the probes to the top of the exhaust (cylinder flange)? 3-4 inches is ideal, anything less than 2 inches (and in some cases less than 3 inches at very high power) is likely to cause much higher than normal EGT readings.

That's three things, did you mean three or is there a fourth? Given that my mechanic has checked the timing repeatedly, if those are the only three then that means an exhaust valve leak is really the only possibility left.

The fourth is anything that causes the mixture to be insufficiently rich.

 

[azure]

Out of the box, Continental's injector flow rates vary more than +/-5%. From what I've heard Lycoming injectors are a little better but I think it's quite possible that you one of your higher flow rate injectors used to be at the cyl 1 location and it got swapped for one of the lowest flowing injectors.

I seriously doubt he could have swapped injectors without knowing it. He said all he did was rotate each injector so that the "numbers" or "letters" were on top. I'm not sure what they look like or what orientation is correct, so I'm just repeating what he told me, and at different times he used both words.

And between the times when #1 was the first to peak, and Tuesday night when it was the last (though that was on the ground, and under higher power), there was NO maintenance done at all. For that matter, something definitely changed between the flight up to 57D (when all EGTs were no more than 60-70F apart) and the flight back, when #1 was up by 190-250F relative to the others, at similar power settings (24 squared at 2200 MSL).

http://csobeech.com/images/RedBox-Mixture.gif

I think that's the graph I was (mis)remembering the details of. 250 ROP was probably impossible to get to from takeoff until cruise on the way back, unless peak EGT was something like 1650F, which I seriously doubt.

At 75% there's no concern about finding peak as long as you don't take forever. I would have checked that just to see if the peak temp was elevated by a similar amount as the full rich EGT. If I was concerned about detonation and/or if the CHTs were getting uncomfortably hot, I'd just reduce power a bit and then check for the delta from peak EGT.

Sure, but I had just climbed at nearly full power with #1's EGT levels at alarming (to me) levels. I was afraid to do anything that would increase them more, even though I wasn't seeing particularly high CHTs -- in fact, they were basically normal for the conditions (high 200s to low 300s).

How close are the probes to the top of the exhaust (cylinder flange)? 3-4 inches is ideal, anything less than 2 inches (and in some cases less than 3 inches at very high power) is likely to cause much higher than normal EGT readings.

I don't know exactly -- my A&P said they were at various distances and he wasn't sure if they were optimally placed or not. He just didn't want to take on the job of repositioning them. Anyway, what I took away from his explanation of how they are held in place is that it is impossible for a probe to have moved by itself, so the changes in EGT readings on #1 must be caused by something else.

The fourth is anything that causes the mixture to be insufficiently rich.

Which is why we're looking into clogs and induction leaks. Given the info I've added, do you still feel this is barking up the wrong tree?

And thanks, BTW -- you seem to know a lot more about engines than my A&P does, so I value your input.

 

[gismo]

I seriously doubt he could have swapped injectors without knowing it. He said all he did was rotate each injector so that the "numbers" or "letters" were on top. I'm not sure what they look like or what orientation is correct, so I'm just repeating what he told me, and at different times he used both words.

OK. I was thinking "rotate" meant that he moved them from cylinder to cylinder.

[/quote]And between the times when #1 was the first to peak, and Tuesday night when it was the last (though that was on the ground, and under higher power), there was NO maintenance done at all. For that matter, something definitely changed between the flight up to 57D (when all EGTs were no more than 60-70F apart) and the flight back, when #1 was up by 190-250F relative to the others, at similar power settings (24 squared at 2200 MSL).[/quote]
That's consistent with a reduction of fuel flow or an exhaust valve leak. A simple compression test would eliminate the exhaust valve issue.

I think that's the graph I was (mis)remembering the details of. 250 ROP was probably impossible to get to from takeoff until cruise on the way back, unless peak EGT was something like 1650F, which I seriously doubt.

1650 at full power and peak EGT is certainly plausible depending on where the probe is located.

Sure, but I had just climbed at nearly full power with #1's EGT levels at alarming (to me) levels. I was afraid to do anything that would increase them more, even though I wasn't seeing particularly high CHTs -- in fact, they were basically normal for the conditions (high 200s to low 300s).

Low to normal CHTs are a pretty good indication that nothing seriously wrong is going on inside the cylinders. You can get what appear to be normal CHTs with an insufficiently rich mixture if the cowl flaps are open in cruise and/or the OAT is really low but that doesn't sound like the case here.

I don't know exactly -- my A&P said they were at various distances and he wasn't sure if they were optimally placed or not. He just didn't want to take on the job of repositioning them. Anyway, what I took away from his explanation of how they are held in place is that it is impossible for a probe to have moved by itself, so the changes in EGT readings on #1 must be caused by something else.

Got it. Something has changed, probe locations and injector positions haven't.

Which is why we're looking into clogs and induction leaks. Given the info I've added, do you still feel this is barking up the wrong tree?

I doubt that you're seeing the result of an induction leak, at least not as long as you were at least 5000 MSL when you found that cylinder 1 was peaking early (higher fuel flow) than you're used to. Up that high you would have the throttle at or near wide open to get 24 inHg of manifold pressure so there's no big pressure difference between the manifold and the air near the engine so a slight leak simply can't flow enough air to affect the mixture in a measurable way. Down low where you can pull 28-29 inHg, running 24 inHg MP means there's 5-6 inHg across the leak to push extra air in. BTW the Lycoming fuel injection system is more sensitive to induction leaks than the Continental version in that a leak on one cylinder will make them all leaner on a Lycoming.

And thanks, BTW -- you seem to know a lot more about engines than my A&P does, so I value your input.[/QUOTE]

 

[azure]

That's consistent with a reduction of fuel flow or an exhaust valve leak. A simple compression test would eliminate the exhaust valve issue.

Which is what I asked him to do... but I think he considers it unlikely enough that he is considering that test low priority.

1650 at full power and peak EGT is certainly plausible depending on where the probe is located.

But is it likely at 2200 MSL and similar ambient temps to on the ground, given that the cylinder peaked on the ground at 1520?

Low to normal CHTs are a pretty good indication that nothing seriously wrong is going on inside the cylinders. You can get what appear to be normal CHTs with an insufficiently rich mixture if the cowl flaps are open in cruise and/or the OAT is really low but that doesn't sound like the case here.

No, definitely not. OAT was about 40F and cowl flaps were closed -- I considered leaving them open, but given the normal CHTs, there didn't seem to be any reason to, and I was fighting a stiff headwind anyway.

I doubt that you're seeing the result of an induction leak, at least not as long as you were at least 5000 MSL when you found that cylinder 1 was peaking early (higher fuel flow) than you're used to.

Well no, I've observed this several times at low altitudes over the last couple of weeks. Low == 3500 MSL at most, and more typically 2500-3000.

 

[gismo]

Which is what I asked him to do... but I think he considers it unlikely enough that he is considering that test low priority.


But is it likely at 2200 MSL and similar ambient temps to on the ground, given that the cylinder peaked on the ground at 1520?
No. With a full rich mixture, the EGT ought to be lower at 2200MSL than on the ground at 980 MSL on the same day. That said, finding peak during a ground runnup might not be very accurate given the issues with rising CHTs and insufficient cooling so maybe you could have gotten a higher EGT on the ground (I know you said the mixture was leaned quite slowly so maybe this is a bad guess). Also FWIW if you were getting detonation by running near peak EGT at full power, that in itself would lower the EGT. Detonation causes the combustion to complete quite earlier than it would with a normal burn leaving more time for the gas to cool before the exhaust valve opens. In addition more heat is transferred to the piston and cylinder head so there's less energy in the exhaust if detonation is occurring.

Well no, I've observed this several times at low altitudes over the last couple of weeks. Low == 3500 MSL at most, and more typically 2500-3000.

OK, at that altitude you've probably got the throttle significantly closed with 3-4 inHg between the manifold and ambient so a leak would have noticeable effects. Perhaps you could check the cylinder EGT peak order at 7000-8000 PA? If that gets cyl 1 to peak later than 2 you almost certainly have a leak that's affecting cylinder 1. On your engine cyl 1 is up front. I wonder if your engine has a balance tube connecting the left and right intake runners up front like the Continentals do. If it's connections could be the leak source.

BTW a common method for locating intake leaks is to plum the output of a shop vac (clean the vacuum insides first) into the throttle body and apply soapy water to all the joints while running the vac.

 

[azure]

Also FWIW if you were getting detonation by running near peak EGT at full power, that in itself would lower the EGT. Detonation causes the combustion to complete quite earlier than it would with a normal burn leaving more time for the gas to cool before the exhaust valve opens. In addition more heat is transferred to the piston and cylinder head so there's less energy in the exhaust if detonation is occurring.

Okay, it sounds like you'd expect a rapidly rising CHT on a cylinder with detonation going on. We didn't see that on #1, but somehow #2 went up 60F or so over a short time, less than a minute, so I'm still a little worried about that cylinder.

Perhaps you could check the cylinder EGT peak order at 7000-8000 PA? If that gets cyl 1 to peak later than 2 you almost certainly have a leak that's affecting cylinder 1.

Unfortunately I asked my A&P to get to work on it before posting here, so it's all disassembled right now (and to make matters worse, he's not answering his phone, so it's a good chance he's gone hunting up north). I may try that if his injector cleaning/replacing all the gaskets doesn't fix it (still not sure where those gaskets are, whether they're on the injectors or the intake pipes).

 

[azure]

Well some good news -- finally heard back from my A&P and (among other things) he did a compression check on #1. He got 77/80. So it's apparently not an exhaust valve leak.

But he still has no idea what the problem is and is just hoping that at least something he's done has fixed the problem. But he hasn't run it up yet to determine that, and has no idea when he'll be able to get back to it. So all I can do at this point is wait... and wait.

 

[azure]

I just got a call from my A&P. He's found that the problem is an intermittent 50% blockage in #1, dx'd by disconnecting the injectors from the cylinders and using the boost pump to force fuel through the lines. The problem is he doesn't know (a) just what the blockage is due to nor (b) exactly where it is, i.e. whether it's in the injector, the line between the fuel divider and the injector, the fitting between the line and the divider, or in the divider itself. Hopefully once he figures that out, he'll be able to clean it out, since otherwise it might be a several AMU expense, depending on what part needs replacement.

 

[azure]

And he claims to have cured it by ultrasonically cleaning the injectors. I flew it last night and EGTs were all normal. Hopefully it is really FIXED and not just sleeping. I really, really hate intermittents.

For now though, it's time to go fly.

 

[Skylane81E]

Woot!

 

[MarcBourget]

Sounds suspicious to me as well. Curious, what work was done the last time the injectors were removed? If they Mech didn't have the diligent to get the injectors installed the way he now says they should be, I wonder if he got the baffles back where they belong?

Onward and upward

Marc Bourget

 

[azure]

Sounds suspicious to me as well. Curious, what work was done the last time the injectors were removed?

Well, he was investigating high RPM drops during run-up mag check, which I got quite suspicious about during the summer. He suspected the fuel servo but wanted to clean the injectors first. He also fixed an induction leak. Then when the one cylinder EGT went up after he put it back together again, he fixed yet another induction leak, then diagnosed the blockage in injector #1.

If they Mech didn't have the diligent to get the injectors installed the way he now says they should be, I wonder if he got the baffles back where they belong?

I asked him specifically about that -- nicely though! He's quite sure he reinstalled the baffles correctly. In any case, the problem seems to be gone now. And in the cold weather, the RPM drops are well within acceptable limits. As long as nothing new crops up, I may wait until annual to have the fuel servo inspected and overhauled if needed.

 

[Flying Ant]

I wouldn't fire your mechanic right away. I read through all the posts as I'm chasing a similar problem and I think his trouble shooting steps were right on.

The injector nozzles in a Lycoming IO-360 have an air bleed hole on one flat and an identification mark stamped on the other. When inserted they need to be screwed in so that the mark is on the bottom so the bleed hole is on the top so fuel can't dribble out after shutdown on the hot engine.

With your symptoms the first thing I would have done is bottle flow check the injectors and if I found a discrepancy, clean the and see if that fixes it....

which from what I read is exactly what your mechanic did and it's now resolved?

Hats off to him I say.

BTW, if you think you have a leaking exhaust valve and you're really worried about it ask your mechanic to borescope that cylinder, although by the looks of your compression numbers it sounds like it's not an issue.

 

[Henning]

If you mean the JPI exhaust temperature sensors, according to my A&P they're welded on (makes sense) and moving them so they're all the same distance from the flame is something he didn't really want to tackle right now. I don't think he'd feel any differently about swapping them.

That's the last straw, either you have the most f-ed up jury rigged plane on the planet ot your mechanic is cheat/idiot. I keep hearing you relate things from your mechanic that sound like "your muffler bearings are getting worn." and "I needed to realign your hubcaps".

 

[Henning]

I wouldn't fire your mechanic right away. I read through all the posts as I'm chasing a similar problem and I think his trouble shooting steps were right on.

The injector nozzles in a Lycoming IO-360 have an air bleed hole on one flat and an identification mark stamped on the other. When inserted they need to be screwed in so that the mark is on the bottom so the bleed hole is on the top so fuel can't dribble out after shutdown on the hot engine.

With your symptoms the first thing I would have done is bottle flow check the injectors and if I found a discrepancy, clean the and see if that fixes it....

which from what I read is exactly what your mechanic did and it's now resolved?

Hats off to him I say.

BTW, if you think you have a leaking exhaust valve and you're really worried about it ask your mechanic to borescope that cylinder, although by the looks of your compression numbers it sounds like it's not an issue.

And misalignment will stall the engine how? The key to diagnostics is not to look at every possible problem, it's to look at the problems that could be causing the symptoms.

 

[denverpilot]

That's the last straw, either you have the most f-ed up jury rigged plane on the planet ot your mechanic is cheat/idiot. I keep hearing you relate things from your mechanic that sound like "your muffler bearings are getting worn." and "I needed to realign your hubcaps".

It's all ball bearings these days.

 

[Flying Ant]

I never said that misaligned injector nozzles could "stall the engine", unless of course you let the clutch out too fast on a hill start

I wrote that because there seemed to be confusion as to what the injector alignment was for.

As for the mechanic being a cheat, from what I read his first trouble shooting suggestions were the cheap easy things and it turned out he was right. I think azure is getting a little bit confused as to what the mechanic is telling her, in one post the EGT probes are welded on and in the next the are attached by a clamp.

Perhaps the mechanic was saying they are clamped in and to move them would require welding because he would have to drill a new hole and weld the old one.

P.S. I love that saying about loading the parts cannon with money and shooting it at the airplane.

 

[azure]

The issue was resolved a couple of months ago by him carefully cleaning the injectors, then switching them around to see whether the problem followed the injectors if it recurred. It didn't.

The position of the bleed hole was probably a red herring all along, although changing the orientation of the injector might have enabled whatever crud was in there for who knows how long to become a fuel flow obstruction with the help of gravity.

Perhaps the mechanic was saying they are clamped in and to move them would require welding because he would have to drill a new hole and weld the old one.

Yep, that's exactly what he was saying, as it turned out. I think I wrote that higher up in the thread, in fact. He usually works on my plane in the wee hours of the morning, so I get his explanations after the fact and over the phone, which is not the best setting to try to understand exactly what he is saying. It would be a lot better (for me, anyway) if I could ask questions in person while he has the thing disassembled, but with my work schedule and his, that's not going to happen very often.

 

[gismo]

The issue was resolved a couple of months ago by him carefully cleaning the injectors, then switching them around to see whether the problem followed the injectors if it recurred. It didn't.

The position of the bleed hole was probably a red herring all along, although changing the orientation of the injector might have enabled whatever crud was in there for who knows how long to become a fuel flow obstruction with the help of gravity.

FWIW, the folks at GAMI (who have a lot of experience with injector issues) claim that the #1 cause of obstructed injectors is cleaning. Apparently it's all too common for a tiny bit of debris floating around in the cleaning fluid (if reused) or the container used for soaking injectors (I've never seen anyone use something spotless for that) to end up lodged in the small passages. Another, perhaps even more common issue occurs if the mechanic uses any kind of shop rag in the cleaning process as the smallest bit of cloth fiber can do the damage. They (GAMI) recommend NOT cleaning injectors at each annual inspection and relying on indications from engine monitors to determine when a specific injector needs cleaning and then doing nothing to that injector except soak it in an appropriate solvent (#9 Hoppes is the favorite of many).

 

[azure]

FWIW, the folks at GAMI (who have a lot of experience with injector issues) claim that the #1 cause of obstructed injectors is cleaning. Apparently it's all too common for a tiny bit of debris floating around in the cleaning fluid (if reused) or the container used for soaking injectors (I've never seen anyone use something spotless for that) to end up lodged in the small passages. Another, perhaps even more common issue occurs if the mechanic uses any kind of shop rag in the cleaning process as the smallest bit of cloth fiber can do the damage. They (GAMI) recommend NOT cleaning injectors at each annual inspection and relying on indications from engine monitors to determine when a specific injector needs cleaning and then doing nothing to that injector except soak it in an appropriate solvent (#9 Hoppes is the favorite of many).

I'm not sure whether he cleaned the injectors at annual or not, but that's a good point and I'll specifically ask him NOT to next time unless there's a reason. In this case there obviously was. I remember him saying that he didn't want to stick anything into the injectors for just the reason you say. I know that he soaked them in solvent more than once to no avail. In the end I think he used some kind of pressurized delivery system to force the solvent through the injectors -- I never saw it though, and would have to ask him to be sure of what he did.

At this point my only concerning issue with the fuel system is that my indicated fuel flow (Cessna gauge, my JPI doesn't have a fuel flow indicator) is higher than it should be and tends to increase slowly during operation at a constant EGT delta from peak ROP (which for me is usually about 100-110 ROP). In cruise at 24/2400 it shows pretty close to 12 gph. My actual fuel usage suggests that the gauge is reading high, by about 1.5 gph or so. However I understand that the gauge is actually a fuel pressure meter calibrated to read in gph and wonder if this could be another partial obstruction somewhere else in the fuel system. With everything firewalled at takeoff, the fuel flow needle edges offscale during the initial climbout until I pull everything back for cruise climb. (I've read from some sources however that that is normal.)

 

[gismo]

At this point my only concerning issue with the fuel system is that my indicated fuel flow (Cessna gauge, my JPI doesn't have a fuel flow indicator) is higher than it should be and tends to increase slowly during operation at a constant EGT delta from peak ROP (which for me is usually about 100-110 ROP). In cruise at 24/2400 it shows pretty close to 12 gph. My actual fuel usage suggests that the gauge is reading high, by about 1.5 gph or so. However I understand that the gauge is actually a fuel pressure meter calibrated to read in gph and wonder if this could be another partial obstruction somewhere else in the fuel system. With everything firewalled at takeoff, the fuel flow needle edges offscale during the initial climbout until I pull everything back for cruise climb. (I've read from some sources however that that is normal.)

Just a wild guess but your fuel pressure (flow) gauge has to have a reference pressure source and if that were somehow blocked you might see peculiar indications. On some airplanes there's are two lines running from the gauge, one to the metered fuel pressure in the injection system and the other to the engine compartment or filtered air between the engine air filter and the throttle body. But chances are the reference pressure port is simply vented into the cabin at the rear of the gauge and I doubt anything could restrict that.

In any case, if EGTs, MP, and RPM are constant and your mixture is set where the slope of EGT vs fuel flow is fairly steep (i.e. between 20 ROP and 100 ROP or 10 LOP to 100 LOP) then you can be pretty certain that the fuel flow isn't changing which means you're seeing some kind of gauging problem (could be the gauge itself). But if the EGTs change when the fuel flow decreases (rise if ROP or fall if LOP) then something is affecting the fuel flow and that should be investigated. BTW are you certain that the mixture control itself isn't moving?

If I were you I would invest in some sort of fuel flow/totalizer. IIRC JPI sells one for less than $500 and the installation isn't terribly labor intensive. Not only would that give you a reliable (and far more accurate) indication of fuel flow, knowing exactly how much fuel remains (baring a leak) can be a significant safety and convenience improvement.

 

[Skylane81E]

High FF on a cockpit pressure type guage is often a blocked injector