Intermittent Rough Engine / High EGT need help diagnosing

[Z W]

I had a M20C with that engine for several years.  It would very quickly foul a plug during taxi if you did not lean it aggressively.  If you forgot to lean, it would remind you at the mag check during run up, where the engine would immediately run very rough and cough and shake.  You could cure it by burning the plug clean.  The procedure was to lean aggressively, set mags to both, set the throttle to 2,000 RPM, lean some more until you saw the RPM drop slightly, and hold it there for 30 seconds to 1 minute.  Then repeat your mag check.  Every time, this would result in a clean plug and a plane ready for takeoff.  I would then smack the back of my head for forgetting to lean, and leave it leaned out until departure.

I assume you did a proper run up and mag check prior to this flight, and did not see the above behavior?  I never took off with a fouled plug and don't know if it would cause what you're seeing, but since this plane is new to you, I thought I'd suggest starting at step one.

If you're able, next time, do a full extended run-up, maybe another test flight if all is good, then download the engine logs from your JPI, and post the links here.  I've done that before and this community is amazing with their ability to look through logs and help you diagnose.

[Z W]

Another thought - You could do the ground run and data download prior to departure without a CFI, I would think, at minimal risk to the plane and your insurance policy.  I think I would do that before scheduling the flight with a CFI and feeling the pressure to fly. 

I will never takeoff in a plane that doesn't show everything normal at run-up on the ground, and I've been pressured by various mechanics and other pilots to do so several times.  In your situation I would even do some extended full-power ground run-ups and hold the engine there for a minute or two to watch the EGTs and CHTs.  Then download the data and share it here.  Once you're confident everything is sorted out on the ground and good to go, you could schedule the CFI with more confidence.

[Shadrach]

Makes me wonder what’s going on with some these O360s. They were designed to run on 100/130 which had almost ~twice the amount of TEL as 100LL.

I asked my dad about ground leaning and plug fowling in the O360s he ooperated in the 60s (M20C and Comanche 180). Ground leaning was was not a thing back then and plug fouling was not common in the higher compression engines designed for 100/130.

 

[takair]

Idle speed during taxi and waiting for takeoff seems to make a difference too.  Throttle pulled to full idle will foul plugs faster than 1000RPM. What was the OP using for ground ops. Also, idle mixture. If it is set for 0 to 10 RPM rise it does much bette than 50 to 100, where many airplanes are set. Tends to require more aggressive leaning for ground ops when the idle mixture is set that far Rich. 

 

 

[Shadrach]

31 minutes ago, takair said:

Idle speed during taxi and waiting for takeoff seems to make a difference too.  Throttle pulled to full idle will foul plugs faster than 1000RPM. What was the OP using for ground ops. Also, idle mixture. If it is set for 0 to 10 RPM rise it does much bette than 50 to 100, where many airplanes are set. Tends to require more aggressive leaning for ground ops when the idle mixture is set that far Rich. 

My idol set on the low side (~500rpm) to minimize landing distances. In terms of ground ops, I think any 4cyl Lycoming should be operated at 900 or above.

[Pinecone]

2 hours ago, Shadrach said:

Makes me wonder what’s going on with some these O360s. They were designed to run on 100/130 which had almost ~twice the amount of TEL as 100LL.

Are you sure about that?

I thought the parallel valve -360s were designed to run on 91/96 AVGAS.    The AEIO-360-B2F in my CAP-10 is a 91/96 engine.

[Shadrach]

31 minutes ago, Pinecone said:

Are you sure about that?

I thought the parallel valve -360s were designed to run on 91/96 AVGAS.    The AEIO-360-B2F in my CAP-10 is a 91/96 engine.

I don’t even think 91/96 was a thing when they were designed. TCDS says min grade of 100/100LL for all 180hp 8.5:1cr O360s. The lower horsepower O360s (168hp) with  7.2:1cr were 80/87.  

[jaylw314]

On 2/15/2024 at 12:42 PM, 33UM20C said:

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

The HP % on the EDM 830 is just calculated from other parameters (MAP, RPM, FF, OAT).  There's a HP constant in the programming menu that requires calibration for your motor, otherwise it could be completely useless.  There's a section on it in the manual, but basically set 70% power in flight according to your POH, then change the HP constant until the HP % actually shows 70%.

That obviously presumes those other parameters and their sensors are also themselves calibrated correctly (thinkin' of you, FF).

Also note that this number is completely useless anyways if you're in a different leaning phase, e.g. if you calibrate it while 125F ROP, it is useless to use at full rich or any other setting.  So if you want to use HP %, calibrate it in the mixture state (like full rich) you want, then remember it is only useful at that mixture.

Edited February 18 by jaylw314

[Shadrach]

8 minutes ago, jaylw314 said:

The HP % on the EDM 830 is just calculated from other parameters (MAP, RPM, FF, OAT).  There's a HP constant in the programming menu that requires calibration for your motor, otherwise it could be completely useless.  There's a section on it in the manual, but basically set 70% power in flight according to your POH, then change the HP constant until the HP % actually shows 70%.

That obviously presumes those other parameters and their sensors are also themselves calibrated correctly (thinkin' of you, FF).

Also note that this number is completely useless anyways if you're in a different leaning phase, e.g. if you calibrate it while 125F ROP, it is useless to use at full rich or any other setting.  So if you want to use HP %, calibrate it in the mixture state (like full rich) you want, then remember it is only useful at that mixture.

But he’s not in different leaning phases. He has the manifold pressure and prop set for 80% power and full Rich Per the POH. So either his fuel flow reading is wrong or the carb is running lean

[EricJ]

3 hours ago, Shadrach said:

I don’t even think 91/96 was a thing when they were designed. TCDS says min grade of 100/100LL for all 180hp 8.5:1cr O360s. The lower horsepower O360s (168hp) with  7.2:1cr were 80/87.  

Note 9 says 91/96 for certain M20C serial numbers.   Remember 100LL wasn't even introduced until the 1970s, so the usual fuel available before that was 80/87, 91/96 and 100/130 or, if you were in a military flying club overseas, 115/145   ;).     The engines weren't originally designed for 100LL because it didn't exist at the time.   I can't find a TCDS rev early enough to show that, but the 100LL on the later TCDS was certainly due to a revision at some point.

[Shadrach]

Just now, EricJ said:

Note 9 says 91/96 for certain M20C serial numbers.   Remember 100LL wasn't even introduced until the 1970s, so the usual fuel available before that was 80/87, 91/96 and 100/130 or, if you were in a military flying club overseas, 115/145   ;).     The engines weren't originally designed for 100LL because it didn't exist at the time.   I can't find a TCDS rev early enough to show that, but the 100LL on the later TCDS was certainly due to a revision at some point.

Yea, that was my point. 100/130 has double the TEL.  I was looking at the And according to the Lycoming TCDS (E286) I was referencing, the 8.5:1CR engines have a min grade of 100/130. There are no Mooney serial numbers in Lycoming’s TCDS. I will give it another look to verify I did not misread anything.

[EricJ]

5 minutes ago, Shadrach said:

Yea, that was my point. 100/130 has double the TEL.  I was looking at the And according to the Lycoming TCDS (E286) I was referencing, the 8.5:1CR engines have a min grade of 100/130. There are no Mooney serial numbers in Lycoming’s TCDS. I will give it another look to verify I did not misread anything.

I was referencing the Note 9 in the Mooney TCDS, which is relevant:

NOTE 9: 91/96 Min. grade aviation gasoline acceptable for Model M20C aircraft, Serial Nos. 1940 through 3184.

I didn't look at the Lycoming TCDS.
 

[Shadrach]

36 minutes ago, EricJ said:

I was referencing the Note 9 in the Mooney TCDS, which is relevant:

NOTE 9: 91/96 Min. grade aviation gasoline acceptable for Model M20C aircraft, Serial Nos. 1940 through 3184.

I didn't look at the Lycoming TCDS.
 

The discussion was around what the engine was designed to run on which I believe was the long since discontinued 100/130. That’s why I am surprised they’re loading up on 100LL

[EricJ]

4 minutes ago, Shadrach said:

The discussion was around what the engine was designed to run on which the long since discontinued 100/130. That’s why I am surprised they’re loading up on 100LL

I agree!   It is definitely a thing, though.   And I also don't recall plug fouling being an issue when we ran 115/145 in our club Cessnas in the 70s, which had even more lead.   I don't know why it is a bigger issue now, but it does seem to be.

 

 

[Z W]

The plug fouling could have been related to that particular plane's setup, I don't know.  I was told it was because the carb was set for sea level ops, and my home base was at an elevation of 1,000 feet.  But it would foul quickly during taxi at full rich mixture.

[jaylw314]

On 2/18/2024 at 12:55 PM, Shadrach said:

But he’s not in different leaning phases. He has the manifold pressure and prop set for 80% power and full Rich Per the POH. So either his fuel flow reading is wrong or the carb is running lean

It was stated as a general caveat, not an instruction.  I thought that was communicated clearly but apparently it didn't come across

Edited February 19 by jaylw314

[33UM20C]

UPDATE: 

I went out yesterday and tried to get it started to no avail (with a preheat). With no preheater available today (as is most days) and no electricity to plug into I created a little battery cart that converts DC batteries to A/C power that my block heater can run on.

So today I hooked it up to the block heater while I pulled the cowl off etc. All plugs and leads looked fine to me but the champion plugs got ~300 hrs. on them as is and show a little wear n tear. Since I don't have a tester I said screw it and replaced all 8 with Tempest UREM38E's (massive). 

With the cowling open to the wind and preheater only on for 1.5 hrs. the oil was about 50 deg F when I went to start. It was a little hard to start but started on my second round of 10 seconds on the starter. 

Everything ran as normal passed a regular runup, LOP runup, WOT runup, and flew great. All EGT's stayed normal and within 15 deg of each other on the WOT test. All CHT's stable as well. No shake in flight. So this seemed to of done the trick. 

I'm also burning 19 GPH on takeoff instead of the 11.3 I had last week.

Thanks everyone for they're input I learned a lot!

[Ragsf15e]

1 hour ago, 33UM20C said:

UPDATE: 

I went out yesterday and tried to get it started to no avail (with a preheat). With no preheater available today (as is most days) and no electricity to plug into I created a little battery cart that converts DC batteries to A/C power that my block heater can run on.

So today I hooked it up to the block heater while I pulled the cowl off etc. All plugs and leads looked fine to me but the champion plugs got ~300 hrs. on them as is and show a little wear n tear. Since I don't have a tester I said screw it and replaced all 8 with Tempest UREM38E's (massive). 

With the cowling open to the wind and preheater only on for 1.5 hrs. the oil was about 50 deg F when I went to start. It was a little hard to start but started on my second round of 10 seconds on the starter. 

Everything ran as normal passed a regular runup, LOP runup, WOT runup, and flew great. All EGT's stayed normal and within 15 deg of each other on the WOT test. All CHT's stable as well. No shake in flight. So this seemed to of done the trick. 

I'm also burning 19 GPH on takeoff instead of the 11.3 I had last week.

Thanks everyone for they're input I learned a lot!

One thing to keep an eye on… new plugs could “fix” the problem only for something to reoccur.  Like something causing fouling or whatever.  Normally plugs (even massives) will be fine well past 300h.  You just clean them annually and check the resistance as described in the videos posted above.

Glad it’s working for you!  Enjoy!

[Pinecone]

On 2/18/2024 at 3:09 PM, Shadrach said:

I don’t even think 91/96 was a thing when they were designed. TCDS says min grade of 100/100LL for all 180hp 8.5:1cr O360s. The lower horsepower O360s (168hp) with  7.2:1cr were 80/87.  

91/96 predates 100/130 which is from the 1940s.

You would need to find the tables from the early 60s, as 91/96 went away around then.

But my CAP-10 has an AEIO-360-B2H and it says minimum grade 91/96 in the POH (1983)

I just checked, the Cherokee 180D POH also states minimum fuel grade of 91/96

 

[Shadrach]

1 hour ago, Pinecone said:

91/96 predates 100/130 which is from the 1940s.

You would need to find the tables from the early 60s, as 91/96 went away around then.

But my CAP-10 has an AEIO-360-B2H and it says minimum grade 91/96 in the POH (1983)

I just checked, the Cherokee 180D POH also states minimum fuel grade of 91/96

 

I don't really care what the aircraft manufacturer says regarding this particular subject.  The engine has its own TCDS independent of the airframes applications.  Yes, the aircraft manufacturer can include revised data in their TCDS.  However, according to the Lycoming TCDS, the minimum grade for all 8.5:1 O360s was 100/130.

[EricJ]

2 hours ago, Shadrach said:

I don't really care what the aircraft manufacturer says regarding this particular subject.  The engine has its own TCDS independent of the airframes applications.  Yes, the aircraft manufacturer can include revised data in their TCDS.  However, according to the Lycoming TCDS, the minimum grade for all 8.5:1 O360s was 100/130.

The airframe TCDS supercedes the engine TCDS, though, in order to account for installation dependencies, etc.   For example, operating temps are effected by cowl design, etc., so are dictated by the installation.   If the airframe TCDS says 91/96 (or whatever) is okay, then it's okay.   The certification process is supposed to verify the differences, so that the Limitations section of the POH/AFM is correct (which is why it is "FAA Approved").

[Shadrach]

1 hour ago, EricJ said:

The airframe TCDS supercedes the engine TCDS, though, in order to account for installation dependencies, etc.   For example, operating temps are effected by cowl design, etc., so are dictated by the installation.   If the airframe TCDS says 91/96 (or whatever) is okay, then it's okay.   The certification process is supposed to verify the differences, so that the Limitations section of the POH/AFM is correct (which is why it is "FAA Approved").

quite a bit of drift here. The discussion about what was not about what was legal to run in the engine.  The discussion centered around what the engine was designed to run on and why they’re fouling plugs at 100LL.  At no point did I question the legality of using the long since discontinued 91/96.

[EricJ]

1 hour ago, Shadrach said:

quite a bit of drift here. The discussion about what was not about what was legal to run in the engine.  The discussion centered around what the engine was designed to run on and why they’re fouling plugs at 100LL.  At no point did I question the legality of using the long since discontinued 91/96.

Perhaps I misunderstood, but you seemed to be using the Lycoming TCDS as an argument that it was designed to run on 100/130 or 100LL.   The early entries in the M20 TCDS indicate 91/96 and 100LL, and the 100LL would have had to have been added in a revision of the TCDS.   I suspect the Lycoming TCDS has been similarly revised over time, so it's probably not a good indicator of what the engines were "designed to run on", especially when the airframe TCDS show differently.   If one could find very early versions of the relevant Lycoming TCDS it might be more revealing of what fuels were expected for use nearer to the time of design.

 

[Shadrach]

20 minutes ago, EricJ said:

Perhaps I misunderstood, but you seemed to be using the Lycoming TCDS as an argument that it was designed to run on 100/130 or 100LL.   The early entries in the M20 TCDS indicate 91/96 and 100LL, and the 100LL would have had to have been added in a revision of the TCDS.   I suspect the Lycoming TCDS has been similarly revised over time, so it's probably not a good indicator of what the engines were "designed to run on", especially when the airframe TCDS show differently.   If one could find very early versions of the relevant Lycoming TCDS it might be more revealing of what fuels were expected for use nearer to the time of design.

 

I posted an image of the Lycoming TCDS showing a minimum grade of 100/130. None of my comments had anything to do with what was legal/approved to run in various applications. My comments centered on the odd trend for 100LL to foul plugs in an engine approved if not designed for running 100/130 which has a much higher lead content.

[EricJ]

1 hour ago, Shadrach said:

I posted an image of the Lycoming TCDS showing a minimum grade of 100/130. None of my comments had anything to do with what was legal/approved to run in various applications. My comments centered on the odd trend for 100LL to foul plugs in an engine approved if not designed for running 100/130 which has a much higher lead content.

My understanding is that Lycoming made revisions to the engines starting many decades ago, anticipating the same reduction or elimination of lead in the fuel that was happening with autos in the 1970s.  This included harder valve seats, etc.   Some of those revisions may have made a difference in lead tolerance.   I doubt the spark plug implementations have remained static, either, and it's likely that the fuel blends have changed over the years, too, even if they do still have a lot of lead content.   One or more of those changes may have contributed to various changes in behavior like increased plug fouling, etc.   I find it curious as well, but I don't doubt that something changed along the way.