Rough engine in flight

[Derrickearly]

Just finished leaning to peak at 7000 ft, and the engine started running rough. Similar to 3 of 4 cylinders firing. I reverted to full rich. Turned on the boost pump. Cycled left, right and back to both magnetos. No change. Just started to look for a place to make a precautionary landing, and the roughness cleared. I switched fuel tanks, and continued my flight without a recurrence. Any ideas?  I was thinking maybe a bit of water in the fuel. I drained both sumps. The right had a few drops of water, and the left was clear. I was flying on the left when the engine was rough. I also drained the sump in the cockpit during preflight using 5 seconds on both sides. Scratching my head. 

Edited November 5, 2022 by Derrickearly
Grammar

[Lionudakis]

I had a similar occurance KOSH bound over the summer about an hour into flight. only lasted a few seconds. The roughness went away quicker than my elevated pulse. I decided it was a small amount of water, despite the usual sumping. 

[ArtVandelay]

Engine monitor data?

This is an example of what losing a cylinder for a few moments looks like:

[Danb]

Here’s another illustration of dead cylinder, clogged injector.

It does get your attention especially at 500 ft.

[PT20J]

That’s exactly what happened to me on a trip. Happened again a few hours later on the same trip. Pulled the injectors when I got home and found one partially clogged. All good after cleaning them.

[ArtVandelay]

Mine was the flight home from an annual, it went away and didn’t return.

[Derrickearly]

2 hours ago, ArtVandelay said:

Engine monitor data?

This is an example of what losing a cylinder for a few moments looks like:

Thank you!  I didn’t think to look at the egt and cht readings. Now I know what to look for. 

[Derrickearly]

2 hours ago, Danb said:

Here’s another illustration of dead cylinder, clogged injector.

It does get your attention especially at 500 ft.

Thank you!  I didn’t think to look at the egt and cht readings. Now I know what to look for. 

[Derrickearly]

Sounds like I should discuss this with my mechanic. 

[A64Pilot]

I think you need to replace fuel cap O-rings, any amount of water is not a normal condition, you should never find water.

I’ve never seen water come from anywhere except a leaking fuel cap myself

[Hank]

1 hour ago, A64Pilot said:

I think you need to replace fuel cap O-rings, any amount of water is not a normal condition, you should never find water.

I’ve never seen water come from anywhere except a leaking fuel cap myself

Be sure to disassemble the cap and change the little o-ring around the center pin. You'll need a new, small cotter pin to put it back together. 

[PT20J]

The fuel lines do not feed from the bottom of the tanks. That’s why there is so much unusable fuel. It takes a lot of water in the tank to get to the engine and then it will likely just quit.

[ArtVandelay]

5 hours ago, PT20J said:

The fuel lines do not feed from the bottom of the tanks. That’s why there is so much unusable fuel. It takes a lot of water in the tank to get to the engine and then it will likely just quit.

Shouldn’t be any water if you’ve sampled your tanks during preflight.