What's my engine monitor telling me?

[Jim_R]

At my annual this year, we installed an Insight G3 engine monitor on my PA28-180 (Lycoming O360-A4A). I've been collecting and reviewing data post-flight, and there's a signature on cylinder 1 that I don't understand.

On my engine, cylinder 1 is farthest forward, then 2-3-4 towards the aft. It's pretty intuitive that cyl 1 would run coolest, with temps increasing to a max at cyl 4. Often, that's exactly what I see in the data, and each cylinder follows a very similar temp profile, just offset from each other with cyl 1 on the bottom and cyl 4 on top of the graph.

However, many of the plots show an odd signature on cylinder 1 when power is applied. Instead of temps ramping up with the other cylinders, they dip. This only seems to occur in flight, never during run-ups on the ground.

I am not sure how to interpret this. I think that's an indication the cylinder is running rich, so perhaps a plug misfire?

How should I troubleshoot this? Should I swap plugs to another cylinder and see if the behavior follows? (Should I swap top and bottom plugs to different cylinders to better see if it follows one or the other?)

Here are two graphs. First one is what I consider a "normal" profile. Second shows the unexpected cylinder 1 behavior. (Graphs 3 and 4 are the same as 1 and 2, but with manifold pressure (which just shows altitude changes since it's a constant-pitch prop) and fuel flow shown to better illustrate engine load.)

I think I've seen in the past where folks have suggested workshops or other methods to better learn how to use/interpret EM data. I'd appreciate a reminder of those!

 

[Sam D]

Did the program you are using come with the engine monitor? I ask because it looks like the stuff from Savvyaviator.com (but guess you wouldn't be asking about workshops if you are already using their site!)

Not sure on the #1 cylinder but the #4 cylinder looks like its getting pretty hot in the climb.

 

[Jim_R]

Did the program you are using come with the engine monitor? I ask because it looks like the stuff from Savvyaviator.com (but guess you wouldn't be asking about workshops if you are already using their site!)

Hah! Well, don't underestimate my cluelessness in this regard. I started out just using Excel, but recently found the Savvy site, and so far had only used the graphing tool instead of spending more time looking around the rest of the place. Apparently, I should do more of that! Thanks for the wakeup call!

Yes, cylinder 4 does get hot sometimes. I've never seen it go far over 400 or stay there too long (now that I know it happens, I try to manage climb rate / airspeed more consciously).

But that's separate from the cyl 1 behavior.

 

[RV10flyer]

Search...Engines: Carbureted vs Fuel Injected.

I would not sweat it too much as individual cylinder fuel metering is not as precise with a carbureted engine. If you had FI, I would definitely look into it deeper. Having a pro look at surely cannot hurt.

Upon reaching 380F, I nose down slightly.

 

[Jim_R]

Again...my question's not about the cyl 4 CHT peaks.

I'm curious to understand the behavior of cyl 1, and why it sometimes dips instead of climbs with the other cylinders.

 

[Jim_R]

So I just spent the last 3 hrs watching a couple of webinars on the Savvy site. While I appreciate the material being made available for free, it was a painful way to get an education. Kept wanting to hit the FF button.

Basically what I got out of all that was, "Your signature doesn't fit any of the classic cases." There was one slide in one of the presentations that said, "Rule of thumb: If both CHT and EGT are moving in the same direction, suspect a fuel issue. If CHT and EGT move in opposite directions, suspect an ignition issue." That was about as close to an answer as I got.

So, following that rule...I should suspect a fuel issue. Which I'm not sure what to do with, since I've got a carbed engine.

Perhaps the right thing to do is drop the $129 and ask a pro to take a look.

 

[flyingcheesehead]

Perhaps the right thing to do is drop the $129 and ask a pro to take a look.

Sounds like an expensive engine monitor.

 

[Computerjim]

It looks like #1 is running a little rich and #4 is running a little lean at full throttle when enrichment is on. What type of airplane and engine?

 

[Geico266]

Fuel injected or carb?


Engine monitors are just that, monitors. Since this is a new monitor on an old engine a prudent course of action would be to do nothing but observe the trend. Make a note of it, collect the data, fly for a year and see if it changes.

This would be a good question to chase down at Oshkosh.

 

[RV10flyer]

What type of airplane and engine?

See post 1, para 1.

 

[Geico266]

See post 1, para 1.

Ah! Thanks!

This is probably the explanation, it is a carbed engine. Uneven fuel distrabution is pretty common in carbed engines. Just monitor the readings and fly.

 

[Jim_R]

Sounds like an expensive engine monitor.

Yes, that's kind of what I was thinking. This thing's supposed to eventually save me money, right?

 

[bbchien]

Jim, see what happens to the relative dip in one when you apply power when Carb Heat is on. Carb heat tends to create turbulence and might even it out- and if it does then you know it a mixture phenomenon.

 

[Jim_R]

Ah! Thanks!

This is probably the explanation, it is a carved engine. Uneven fuel distrabution is pretty common in carved engines. Just monitor the readings and fly.

Um, thanks, but somehow I don't think "oh, just ignore that oddity in your engine monitor data" is good advice. It may be true that this signature is nothing to be concerned about, but I want to actually understand it before I dismiss it. Again, I'm talking about the irregularities in cyl 1, not cyl 4.

Perhaps the signature I'm talking about doesn't jump out to others the way it does to me. See the new attachment where I've highlighted the behavior I'm questioning.

Area 1: Aggressive leaning on ground during extended hold for IFR clearance. CHTs for 2,3,4 rise, but CHT for 1 drops. EGTs appear normal.

Between Area 1 and Area 2 (not circled): Initial full-power climb (sea level to ~1500'). Mixture full rich. All CHTs and EGTs look normal.

Note that fuel pump is turned off after the first climb, and the FF trace jumps up. That is because I could not easily mount the FF sensor downstream of both the engine-driven and electrical fuel pumps, so while the electric pump is on, FF reads lower than actual by roughly half; it's just a sensor issue--the engine is not starved for fuel!

Area 2: Second full-power climb (1500' - 2500'). Mixture still full-rich. Both CHT and EGT drop for cyl 1 while they climb (as expected) for cyls 2-3-4.

Area 3: Third full-power climb to final altitude. Climb begins with mixture full rich; cyls 2-3-4 react as expected, but cyl 1 shows an initial decline in both CHT and EGT, then they turn around and follow the other 3 cyls. As the climb progresses, you can see where the mixture is becoming over-rich, and I start leaning during the climb to maintain power.

 

[RV10flyer]

Area 1: Aggressive leaning on ground during extended hold for IFR clearance. CHTs for 2,3,4 rise, but CHT for 1 drops. EGTs appear normal.

From your first post..."However, many of the plots show an odd signature on cylinder 1 when power is applied. Instead of temps ramping up with the other cylinders, they dip. This only seems to occur in flight, never during run-ups on the ground."

I take it you flew again since first post.

Understand, we are not George Braly, John Deacon or Walter Atkinson, but will try to help. I fly with an EIS connected to my IO-540. Initially, I worried about all of the numbers if they varied too much with power/mixture/IAS/altitude changes. After 124.5 hrs, I know about what it should be reading and when. I have all engine numbers written down on a sheet from several different flights with me for reference. If it is running smooth and numbers " normal" and within mfr limits then it no longer catches my attention. Learn your initial power up for takeoff numbers well! They are in my scan near "airspeed alive, looking for 65 kts" call out to my wife. If anything is out of place or rough running, throttle will be cut.

Now on your #1 issue. Try carb heat as mentioned above. Try the easy stuff first...new plugs, swap sensors, tighten clamps, replace intake gaskets, ensure cylinder shrouds and cowl seals look good, etc Make any change ONE at a time, so you and the rest of the online world will know what fixed it. It could just be due to a richer mixture/more cooling airflow getting to #1 at those dip times. How does it sound/feel with your headset off on one ear during the dips?

 

[Geico266]

Um, thanks, but somehow I don't think "oh, just ignore that oddity in your engine monitor data" is good advice. It may be true that this signature is nothing to be concerned about, but I want to actually understand it before I dismiss it. Again, I'm talking about the irregularities in cyl 1, not cyl 4.

Perhaps the signature I'm talking about doesn't jump out to others the way it does to me. See the new attachment where I've highlighted the behavior I'm questioning.

Area 1: Aggressive leaning on ground during extended hold for IFR clearance. CHTs for 2,3,4 rise, but CHT for 1 drops. EGTs appear normal.

Between Area 1 and Area 2 (not circled): Initial full-power climb (sea level to ~1500'). Mixture full rich. All CHTs and EGTs look normal.

Note that fuel pump is turned off after the first climb, and the FF trace jumps up. That is because I could not easily mount the FF sensor downstream of both the engine-driven and electrical fuel pumps, so while the electric pump is on, FF reads lower than actual by roughly half; it's just a sensor issue--the engine is not starved for fuel!

Area 2: Second full-power climb (1500' - 2500'). Mixture still full-rich. Both CHT and EGT drop for cyl 1 while they climb (as expected) for cyls 2-3-4.

Area 3: Third full-power climb to final altitude. Climb begins with mixture full rich; cyls 2-3-4 react as expected, but cyl 1 shows an initial decline in both CHT and EGT, then they turn around and follow the other 3 cyls. As the climb progresses, you can see where the mixture is becoming over-rich, and I start leaning during the climb to maintain power.

If the cylinder is cooling it is getting more fuel than the others. Since there is nothing you can do my suggestion to just fly it and monitor it is valid. You have zero history that there is a problem since you just installed the monitor. What engine monitors tell you is trends based on history. We see this "panic" in experimentals all the time when someone gets a new plane or adds the latest engine monitor.

Change the sensors, change the plugs, change what ever you want. Rebuild the engine for all I care, then add fuel injection so you can do something about uneven fuel flow.

You have a carborated engine. Assuming the engine is properly tuned up and maintained there is nothing you can do about uneven fuel flow.

 

[Jim_R]

If the cylinder is cooling it is getting more fuel than the others. Since there is nothing you can do my suggestion to just fly it and monitor it is valid.

That is a clearer answer than the first one, and much appreciated. It was not at all clear to me from the first answer whether you were addressing the #1 issue, or what, exactly, your rationale was. Thanks for taking the time to clarify.

 

[Jim_R]

From your first post..."However, many of the plots show an odd signature on cylinder 1 when power is applied. Instead of temps ramping up with the other cylinders, they dip. This only seems to occur in flight, never during run-ups on the ground."

I take it you flew again since first post.

OK, clarification: Until this flight with the extended ground hold, I had never seen a deviation between cylinders on the ground at all, and in flight they had only occurred during an increase in power, and that was in my head when I wrote my OP. While this plot does show a deviation on the ground, it's still not during a run-up. Sorry for any confusion that caused.

Understand, we are not George Braly, John Deacon or Walter Atkinson, but will try to help.

I do understand that, and I appreciate the help. I mostly posted here in case this was a slam-dunk, "Oh, yeah, that's obviously a so-and-so issue. How come you couldn't figure that out yourself?" kind of situation.

Now on your #1 issue. Try carb heat as mentioned above. Try the easy stuff first...new plugs, swap sensors, tighten clamps, replace intake gaskets, ensure cylinder shrouds and cowl seals look good, etc Make any change ONE at a time, so you and the rest of the online world will know what fixed it. It could just be due to a richer mixture/more cooling airflow getting to #1 at those dip times. How does it sound/feel with your headset off on one ear during the dips?

Short answer is, I have never noticed any change in sound/pitch/smoothness in the engine during these times. Never knew they were happening until I got the monitor.

I will continue to scratch my head on this one. Thanks for the suggestions.