Engine misfire on climb and cruise

[PT20J]

Since you are getting some gunk in the sumps, it might not hurt to check the gascolator screen and the servo inlet filter screen.

[jlunseth]

I did this to myself once. I unwittingly took off with the key switched to just one mag. Had some misses, went back and landed, figured out what I did, dropped the passenger off so I could test fly, and the test flight was perfect, no problem. Which may tell you it could have been (1) pilot error, although the fact that it did the same thing on subsequent flights mitigates against that unless you are making the same mistake, (2) a flaw in the ignition switch, you do know there is an AD that requires periodic testing of the switch (that we all forget to comply with)?, or (3) one mag gone or going bad. On three, I have seen issues where a track develops across the cap that allows the electricity to go to the wrong place, and also corrosion in one or more sockets in the cap or in one or more spark plug harness ends that go in the sockets. 

[ArtVandelay]

Since you are getting some gunk in the sumps, it might not hurt to check the gascolator screen and the servo inlet filter screen.

How many screens are there, in order:
Fuel pickup, gascolator, servo inlet?

My J has an extra one on the outlet side of the electric fuel pump behind a panel that’s not removed unless you’re going to R/R the boost pump.

[PT20J]

33 minutes ago, ArtVandelay said:

How many screens are there, in order:
Fuel pickup, gascolator, servo inlet?

My J has an extra one on the outlet side of the electric fuel pump behind a panel that’s not removed unless you’re going to R/R the boost pump.

That's it, I think. The extra filter is only on the models with early Dukes boost pumps. SB M20-222B.

[Guest]

1 hour ago, ArtVandelay said:

How many screens are there, in order:
Fuel pickup, gascolator, servo inlet?

My J has an extra one on the outlet side of the electric fuel pump behind a panel that’s not removed unless you’re going to R/R the boost pump.

When that Airmaze filter was added by AD and SB, they neglected to mention servicing it ever.  It should be done on your Annual inspection.

[redbaron1982]

Hey, a quick update on this, I got a reply from Savvy (great first impression, they process my case in less than 6 hours!) and they say that there are misfires in Cyl #3, most evident at the end of the flight. Now that I know where to look it does seem that EGT of Cyl 3 is not correct. This is the last part of the flight, where according to Savvy there were a lot of misfires:

 

And here a previous flight, without misfires:

In the first one Cyl #3 is not tracking the other cylinder and seems to be more erratic, while in the second one, they all move more or less in sync.

I will get the Cyl #3 spark plugs checked.

 

[PT20J]

46 minutes ago, M20Doc said:

When that Airmaze filter was added by AD and SB, they neglected to mention servicing it ever.  It should be done on your Annual inspection.

Out of curiosity, I looked at SB M20-222B and it says "...and allow material to be removed from the system during inspection periods." Mooney seems to have left this off the annual/100 hour inspection checklist. But, from the wording of the service bulletin, I take it to imply 100/hr or annual inspections. 

I've never seen one. I assume that they can be opened and inspected since the purpose it to trap particles from a deteriorating Dukes boost pump. Presumably one would want to inspect it to see if the pump is shedding material and should be replaced or overhauled.

Skip

[Guest]

14 minutes ago, PT20J said:

Out of curiosity, I looked at SB M20-222B and it says "...and allow material to be removed from the system during inspection periods." Mooney seems to have left this off the annual/100 hour inspection checklist. But, from the wording of the service bulletin, I take it to imply 100/hr or annual inspections. 

I've never seen one. I assume that they can be opened and inspected since the purpose it to trap particles from a deteriorating Dukes boost pump. Presumably one would want to inspect it to see if the pump is shedding material and should be replaced or overhauled.

Skip

There are no instructions on disassembling or cleaning and no part numbers for O rings to reassemble it.  An obvious omission by Mooney and the FAA.

[redbaron1982]

BTW today I checked to see if I could see anything obviously wrong with a lead wire or anything else and although I didn't find anything I did find that the leads are touching sharp aluminum edges.

Is it ok to have this kind of things after a annual from Maxwell? For me is seems like it should have come up in the annual and be fixed.

Suggestions on how I can fix it?

 

[A64Pilot]

Replace the grommet to fix the sharp edges, it’s very easy simply get the right size and cut it and install it, to install without cutting is labor intensive and not in my opinion worth doing.

People miss things, a “perfect” Annual most of us couldn’t afford.

According to Lycoming intermittent missing in flight could be a sticking valve, not all sticking valves manifest as morning sickness.

However with recently overhauled mags, I’d suspect them. Starting with a point gap check is in my opinion a likely problem and very easy to inspect and eliminate.

I like to start with the inexpensive, easy problems and eliminate them first. But once you eliminate the ignition system as a possibility if that doesn’t fix it, I think I’d look at the valves in that one cylinder, most likely the exh valve of course.

[JayMatt]

18 hours ago, Shadrach said:

Some pilots like to make complex aircraft operations more complex than needed.

Agreed. Sometimes we forget an engine is an engine is an engine. It's not rocket science

[Shadrach]

22 hours ago, N201MKTurbo said:

When the point gap is next to nothing, it will work when the engine is cold. As it heats up the gap goes to nothing and one of the mags stops firing. The engine doesn't quit, but you can feel it. it will usually go on and off every few seconds kind of a thing. It feels like a misfire. You can see all your EGTs rise when it stops firing.

Agree that you can feel a mag drop off line as I have experienced it a few times.  However, none of mine have felt like a "misfire". More a just perceptible rpm drop until the governor responds.  Last time it happened neither pax nor copilot picked it up.  I felt it and my suspicions were confirmed by an across the board increase in EGTs. I was LOP in cruise at the time. I suspect the symptoms would be diminished in full rich climb. Also, if the effective gap goes to 0 because of heat, wouldn't that cause the mag to drop off completely rather than intermittently?   I am not doubting your theory or experience. I am just trying to get my head around the scenario and symptoms.

[Shadrach]

21 hours ago, jlunseth said:

I did this to myself once. I unwittingly took off with the key switched to just one mag. Had some misses, went back and landed, figured out what I did, dropped the passenger off so I could test fly, and the test flight was perfect, no problem. Which may tell you it could have been (1) pilot error, although the fact that it did the same thing on subsequent flights mitigates against that unless you are making the same mistake, (2) a flaw in the ignition switch, you do know there is an AD that requires periodic testing of the switch (that we all forget to comply with)?, or (3) one mag gone or going bad. On three, I have seen issues where a track develops across the cap that allows the electricity to go to the wrong place, and also corrosion in one or more sockets in the cap or in one or more spark plug harness ends that go in the sockets. 

I had a similar experience when my ignition switch rotated clockwise in the panel.  The switch indexes (unbeknownst to me) no longer matched the labels in such a way the the "both" was actually "left".  Full rich climb performance was diminished, but the engine ran as smooth as ever. Why would your engine miss on a single mag? It's not supposed to.

[Shadrach]

16 hours ago, redbaron1982 said:

BTW today I checked to see if I could see anything obviously wrong with a lead wire or anything else and although I didn't find anything I did find that the leads are touching sharp aluminum edges.

Is it ok to have this kind of things after a annual from Maxwell? For me is seems like it should have come up in the annual and be fixed.

Suggestions on how I can fix it?

 

While that is not pretty, someone placed that blob of RTV there to prevent chafing.  Can the group confirm that this is how all J models are routed? Are all of the top leads routed through a single grommet?   My F has "2 wire" plates  (shown below) that secure the leads where they pass through the rear baffle wall. They are obnoxiously expensive (>$60 Each)

[redbaron1982]

I want to take advantage of this to give a quick PIREP on SavvyAviation, I think most of you guys are already familiar with it, but anyway. Great service, great value. For me is a no brainier to have their analysis service. The cost/benefit is huge.

The value of your engine, aircraft and even more your life way outweighs the yearly cost of Savvy.

Edited March 23, 2023 by redbaron1982

[Shadrach]

21 minutes ago, redbaron1982 said:

I want to take advantage of this to give a quick PIREP on SavvyAviation, I think most of you guys are already familiar with it, but anyway. Great service, great value. For me is a no brainier to have their analysis service. The cost/benefit is huge.

The value of your engine, aircraft and even more your life way out weights the yearly cost of Savvy.

Good to know Savvy has identified the misfire. Have they offered theories as to a potential cause?

[redbaron1982]

20 minutes ago, Shadrach said:

Good to know Savvy has identified the misfire. Have they offered theories as to a potential cause?

Spark plugs, I'll have those checked next Monday.

[N201MKTurbo]

2 hours ago, Shadrach said:

Agree that you can feel a mag drop off line as I have experienced it a few times.  However, none of mine have felt like a "misfire". More a just perceptible rpm drop until the governor responds.  Last time it happened neither pax nor copilot picked it up.  I felt it and my suspicions were confirmed by an across the board increase in EGTs. I was LOP in cruise at the time. I suspect the symptoms would be diminished in full rich climb. Also, if the effective gap goes to 0 because of heat, wouldn't that cause the mag to drop off completely rather than intermittently?   I am not doubting your theory or experience. I am just trying to get my head around the scenario and symptoms.

But it is a misfire on 1/2 the ignition system. Granted, it isn’t like the whole cylinder not firing.

[jlunseth]

2 hours ago, Shadrach said:

I had a similar experience when my ignition switch rotated clockwise in the panel.  The switch indexes (unbeknownst to me) no longer matched the labels in such a way the the "both" was actually "left".  Full rich climb performance was diminished, but the engine ran as smooth as ever. Why would your engine miss on a single mag? It's not supposed to.

It was awhile ago Ross and since then the mags have both been rebuilt and the plugs and harness have been replaced, so I can't tell you exactly why. But remember, mine is a turbocharged engine. On takeoff, full rich is very rich and probably I was getting weak ignition of a very wet mix. It was a sporadic miss as I recall, but enough to make me want to find out what was wrong so that is what I did. Once I figured out it was the pilot the problem was solved.

[Shadrach]

1 hour ago, N201MKTurbo said:

But it is a misfire on 1/2 the ignition system. Granted, it isn’t like the whole cylinder not firing.

Yes, just like a mag packing it in. Which in my experience causes a very small, almost imperceptible rpm drop for fraction of a second as the governor reacts to the power loss.

[Yetti]

Always start with the simple stuff first.   Pull the plugs they tell a story.   Too rich, Too Lean, Fouled.  Then you can create a plan from there.

[Shadrach]

19 hours ago, jlunseth said:

It was awhile ago Ross and since then the mags have both been rebuilt and the plugs and harness have been replaced, so I can't tell you exactly why. But remember, mine is a turbocharged engine. On takeoff, full rich is very rich and probably I was getting weak ignition of a very wet mix. It was a sporadic miss as I recall, but enough to make me want to find out what was wrong so that is what I did. Once I figured out it was the pilot the problem was solved.

Though it is not supposed to, it is certainly conceivable that the combination of max RPM/piston speed coupled with full rich, single point of ignition (minimum combustion speed) could precipitate a rough running engine.  With much of energy from combustion lagging behind the piston's power stroke and going out the exhaust.  A little leaning would likely bring things back to a sufficiently harmonious state.  My NA IO360 loses a noticeable amount of power when full rich, max RPM on a single mag.  It does not run rough, but EGTs increase significantly. I can get back much of the lost power by leaning a little bit. 

It would not be a bad idea for folks to experiment with single mag operations at altitude so they are more prepared to diagnose and understand how ignition issues can affect combustion.  One of my partners RTB'd and scrubbed a trip because he could not lean the engine upon reaching cruise altitude. It would go rough before peaking on the leanest (#3) or richest (#2) cylinder in spite of a perfect ground run up. He landed, called and told me he had canceled due to mag failure.  It was simply a $hitty Champion spark plug on cyl #1 that was failing under load and going of line at about 2200rpm.  Had he understood what was happening, he'd have only been delayed an hour.