Intermittent Rough Engine / High EGT need help diagnosing

[33UM20C]

Hey guys I'm new here & new to Mooney Ownership!

I recently bought a 1963 M20C with the O-360 A1A. Flying today I ran into some issues (I think) and want to see what you guys think!

This is only in my first couple of flights so don't be afraid to tell me I'm overthinking things and this may be normal.

 

On todays flight I noticed on climb out really high EGT on cylinder #1, it was climbing faster than the others and eventually peaked above red zone at 1670 deg F before I pulled some power and leveled off to let it rest. For reference I was only at maybe 900 FPM so not a harsh climb. I then took the "Climb out" picture. You can see a still quite hot cylinder #1 with a much cooler cylinder 3 / 4. I was able to get it to settle down so I continued my flight in the nearby area by leaning it out to about 75 ROP to cruise to a practice airspace where I entered slow flight and did a couple stalls (2) - in recovery from the second stall into a cruise I noticed the engine seemed quite a bit rougher compared to my initial cruise out which was extremely smooth. I then took the "Cruise 1" picture where you can see cylinder #1 sitting about 150 deg F hotter than the others. At this point I headed back to the airport where I could only get cylinder 1 to cool down when bringing back power for a decent.

Couple things to note:

1. Climb out shows only 11.4 GPH at %80 power mixture full rich. That seems low

2. CHT was completely stable for the whole flight

3. Its 30 deg F OAT today

4. Annual completed 2/10/24 (last week) they found nothing wrong with the engine and / or engine monitor

5. No RPM drop when leaning on taxi

EDIT: 6. Muffler / risers and pipes / interior airbox & baffling are all brand new and sealed

 

I'm thinking its one of these possibilities: 

1. Fouled or bad spark plug on cylinder 1 causing a bad burn and releasing heat into the exhaust?

2. Carb air/fuel mixture is too lean and somehow favoring 2/3/4 over cylinder 1?

3. Possible blockage in a air/fuel path that doesn't allow for MAX flow but is unnoticeable at low power settings and low air/fuel flow?

 

Let me know what you all think. Thanks!

Edited February 15 by 33UM20C
adding info

[Shadrach]

Seems most likely Ignition related. No way an O360 would generate EGTs in the high 1600s from mixture.

[Rwsavory]

Check for an intake leak. 

[hammdo]

Check standby vacuum if you have that too…

-Don

[Shadrach]

20 minutes ago, Rwsavory said:

Check for an intake leak. 

Really unlikely (as in likely not possible) that an intake leak is causing an EGT to flirt with 1700°. 

[hammdo]

#1 and #4 show very different readings - may want to check probes too…

add a little carb heat to see if those level out…

-Don

[Shadrach]

 @33UM20C I’m in your neck of the woods. We should meet up sometime. Too bad you didn’t do an in-flight mag check. I would bet dollars to donuts that you would see EGTs even out but read high on one mag and be running rough (three cylinders) on the other. Verifying the ignition system is working properly is low hanging fruit. It is the first place to start.

[hammdo]

Agree, first ck ignition…, I do a lean run-up to give the ignition a workout before take-off but inflight would tell you for sure…

-Don

[33UM20C]

48 minutes ago, hammdo said:

#1 and #4 show very different readings - may want to check probes too…

add a little carb heat to see if those level out…

-Don

Far as I know the probes were checked at annual because they worked on the JPI and had the exhaust apart to fix a cracked riser (brand new...) but yes carb heat was applied to cool down the cylinder with increased fuel and that worked.

45 minutes ago, Shadrach said:

 @33UM20C I’m in your neck of the woods. We should meet up sometime. Too bad you didn’t do an in-flight mag check. I would bet dollars to donuts that you would see if it is even out on one mag and be running rough on three cylinders on the other. Verifying the ignition system is working properly is low hanging fruit. It is the first place to start.

Yeah I wish I had thought of that while still in flight, I initially expected it to be a fuel issue. I will do this next flight and update the forum. I'm definitely interested in meeting a fellow Mooney owner! Especially so close up in HGR. 

 

At this point I expect I somehow fouled the spark plugs while on the ground (I've only flown in 2 times though). Going to the airport Saturday to do a couple tests but I cant actually fly without a CFI yet because I need my insurance hours.. anyone here a CFI and want to trace this with me?? haha. Il do what I can on the ground I.E pull the cowling, check spark plugs for buildup, check P leads and spark plug connections for good power, and maybe do a lean runup to see if I can get it to run rough on the ground like it did in the air.

Thanks guys!

[PT20J]

EGT on #1 is really high.

It's a carbureted engine and only one cylinder is affected, so that eliminates fuel.

A leaky intake should cause rough running at idle where it has the greatest effect on mixture, so it's probably not that.

Only one cylinder is affected, so it's not timing.

Maybe a spark plug, but that shouldn't cause an EGT that high. Still, wouldn't hurt to check the plugs.

Might be a sticking exhaust valve. That might explain the engine roughness, but I would expect it to also lower CHT. 

Might be the probe. I always verify instrumentation is accurate before tearing into other things. I believe some monitors have a pull up resistor to cause a bad probe to read very high so that the monitor can recognize it and flag it. Since the airplane just came out of maintenance, I'd check all the probe connections and I would also swap probes between #1 and #3 to see if the problem stays with the cylinder or follows the probe.

Skip

 

[Shadrach]

1 hour ago, 33UM20C said:

Far as I know the probes were checked at annual because they worked on the JPI and had the exhaust apart to fix a cracked riser (brand new...) but yes carb heat was applied to cool down the cylinder with increased fuel and that worked.

Yeah I wish I had thought of that while still in flight, I initially expected it to be a fuel issue. I will do this next flight and update the forum. I'm definitely interested in meeting a fellow Mooney owner! Especially so close up in HGR. 

 

At this point I expect I somehow fouled the spark plugs while on the ground (I've only flown in 2 times though). Going to the airport Saturday to do a couple tests but I cant actually fly without a CFI yet because I need my insurance hours.. anyone here a CFI and want to trace this with me?? haha. Il do what I can on the ground I.E pull the cowling, check spark plugs for buildup, check P leads and spark plug connections for good power, and maybe do a lean runup to see if I can get it to run rough on the ground like it did in the air.

Thanks guys!

The plane lives at HGR. I live north in North Frederick county off rt26. My father in law keeps a red Decathlon at FDK. It flies frequently, occasionally by me. I’d love to see your bird sometime.

[Shadrach]

50 minutes ago, PT20J said:

EGT on #1 is really high.

It's a carbureted engine and only one cylinder is affected, so that eliminates fuel.

A leaky intake should cause rough running at idle where it has the greatest effect on mixture, so it's probably not that.

Only one cylinder is affected, so it's not timing.

Maybe a spark plug, but that shouldn't cause an EGT that high. Still, wouldn't hurt to check the plugs.

Might be a sticking exhaust valve. That might explain the engine roughness, but I would expect it to also lower CHT. 

Might be the probe. I always verify instrumentation is accurate before tearing into other things. I believe some monitors have a pull up resistor to cause a bad probe to read very high so that the monitor can recognize it and flag it. Since the airplane just came out of maintenance, I'd check all the probe connections and I would also swap probes between #1 and #3 to see if the problem stays with the cylinder or follows the probe.

Skip

 

Some of my my EGTs get into the 1600s when running on a single ignition source. I would expect slightly higher base line EGTs compared to an angle valve due to the lower (8.5:1) compression ratio.

[hammdo]

One other item to note is the low EGT/CHT on #4 -- that could also indicate a plug not firing or weak ignition issue. 

-Don

[33UM20C]

2 hours ago, hammdo said:

One other item to note is the low EGT/CHT on #4 -- that could also indicate a plug not firing or weak ignition issue. 

-Don

So a plug failure could result in High and low EGT? Could you explain that to me to I could better understand both scenarios?

[hammdo]

Sorry, I should have said both plugs (since I was looking solely @ #4). So if the plugs are not firing @ all or are very weak, less heat is generated thus much lower EGTs/CHTs - a reason to check the ignition. A weak spark may cause the plugs to foul up/soot up and cause weaker spark -- which likely have lower EGT/CHTs for that cylinder.  (off topic a bit - Fast rising CHTs and lower EGTs are pre-ignition - generally hot-spots developed in a cylinder).
 

I had a top and bottom pug in my Warrior fail some years back and they found both plugs had cracks that progressively got worse.  On a single plug, the burning takes a lot longer since a single plug causes the flame front to not burn as fast and you’ll usually see EGTs rise on a single plug.

-Don

. 

 

 

[Shadrach]

17 hours ago, hammdo said:

Sorry, I should have said both plugs (since I was looking solely @ #4). So if the plugs are not firing @ all or are very weak, less heat is generated thus much lower EGTs/CHTs - a reason to check the ignition. A weak spark may cause the plugs to foul up/soot up and cause weaker spark -- which likely have lower EGT/CHTs for that cylinder.  (off topic a bit - Fast rising CHTs and lower EGTs are pre-ignition - generally hot-spots developed in a cylinder).
 

I had a top and bottom pug in my Warrior fail some years back and they found both plugs had cracks that progressively got worse.  On a single plug, the burning takes a lot longer since a single plug causes the flame front to not burn as fast and you’ll usually see EGTs rise on a single plug.

-Don

. 

 

 

1151° Is on the low side but not alarmingly. It’s likely still less than 300° ROP. It would not concern me until I had a reason to believe it was a symptom of a problem. 

[Ragsf15e]

21 hours ago, 33UM20C said:

So a plug failure could result in High and low EGT? Could you explain that to me to I could better understand both scenarios?

And to finish answering for @hammdo, typically if 1 plug isn’t firing in a cylinder, that will show a higher than normal egt as it takes longer to burn the charge from a single ignition point and it’s still hot as it passes the egt probe.

So both bad/misfiring plugs, maybe cold egt, but maybe not.  One misfiring, likely high egt.

That 1600egt reading is pointing at one ignition source not working in that cylinder.  Maybe plug, wires, timing, mag?  Who knows.  If you don’t see it in a normal runup, you might need an airborne full power (65%) lean mag check.

Edited February 17 by Ragsf15e

[hammdo]

Martin Pauly did a video of inflight mag check - just for reference:

-Don

[Pinecone]

An intake leak could cause that cylinder to be lean.

Common practice these days it to climb at full power.  Especially with a carb, as they have an enrichment valve for more fuel at full power.

Yes, 11.4 GPH is low.  You should be around 1 GPH per 10 HP at full power.  So more like in the 18 GPH range.

[Shadrach]

37 minutes ago, Pinecone said:

An intake leak could cause that cylinder to be lean.

Common practice these days it to climb at full power.  Especially with a carb, as they have an enrichment valve for more fuel at full power.

Yes, 11.4 GPH is low.  You should be around 1 GPH per 10 HP at full power.  So more like in the 18 GPH range.

I don’t think a typical O360 will generate will flow at 18gph . 16.5 to 17 is on the upper end for the breed. Agree that 11.4 is low for full rich @ 80%. Should be closer to 12.5-13gph. I’m not sure if this O360 variant has an enrichment circuit. As many C pilots report throttle reductions in climb as a way to manage temps.

[33UM20C]

22 hours ago, hammdo said:

Martin Pauly did a video of inflight mag check - just for reference:

-Don

Super informative video thank you!

I pulled all 4 bottom spark plugs off today and all seems normal. cylinder 3 / 4 plugs has moisture on the threads but I assume that's from unburned fuel at shutdown? 

All looks super clean as they only have about 300 hours on them. I'm going to pull the top 4 Monday. didn't have time today because they're so much harder to get to.. if anyone has tricks to it let me know.

Prob just going to buy a set of 12 Tempest UREM38E massives and put all new plugs in as I hear online some champion plugs have a lot of problems and Tempest will burn better as well as make everything smoother for longer.

 

Attached is what the plug on C#2 looked like. They all looked the same except a little bead of lead on C#3  

 

[hammdo]

You’ll need to check the resistance also — that will also tell you if a plug is ‘off’…

These are fine wire but the concept is the same…

Mike Busch/Savvy video:

-Don

[Shadrach]

3 hours ago, 33UM20C said:

Super informative video thank you!

I pulled all 4 bottom spark plugs off today and all seems normal. cylinder 3 / 4 plugs has moisture on the threads but I assume that's from unburned fuel at shutdown? 

All looks super clean as they only have about 300 hours on them. I'm going to pull the top 4 Monday. didn't have time today because they're so much harder to get to.. if anyone has tricks to it let me know.

Prob just going to buy a set of 12 Tempest UREM38E massives and put all new plugs in as I hear online some champion plugs have a lot of problems and Tempest will burn better as well as make everything smoother for longer.

 

Attached is what the plug on C#2 looked like. They all looked the same except a little bead of lead on C#3  

 

That plug looks perfectly serviceable. I would not start throwing parts at it until you have a diagnosis. An engine monitor can tell you a lot both on the ground and in the air. Why not do as much non invasive analysis as possible before starting to pull and replace parts?

[33UM20C]

2 hours ago, Shadrach said:

That plug looks perfectly serviceable. I would not start throwing parts at it until you have a diagnosis. An engine monitor can tell you a lot both on the ground and in the air. Why not do as much non invasive analysis as possible before starting to pull and replace parts?

I agree,  I should do more testing. 

 

Problem is I cant. Becuase im below my insurance hours minimum I cant fly the plane and I cant get it to recreate the problem on the ground.

 

I need to fly with a CFI but its hard to ask sombody to drive to meet me for a 15 minute diag flight when they live an hr away. By the time im done paying for their drive, air time, and plane tac time. Im in more than the plugs are worth to swap - and id still be running 300 hr massives so.

 

Unfortunate situation but its the one im in.

[Shadrach]

So you did a run up at high RPM with the engine leaned and there was no elevated EGT or roughness during the mag check?