Engine suddenly running very rough

[JackinMichigan]

Had me a bit of a scare today.

Took my RV-10 up for the first time after it's annual inspection. I was about to turn on the downwind leg of the pattern when suddenly the engine started running very rough. My first thought was that something was off balance as the whole plane began shaking (not severely, but enough to have my undivided attention).

I immediately throttled down, turned around as fast as I could, and landed on the opposide end of the runway I had just taken off from. Once safely on the ground I throttled up as fast as I could with the brakes on (about 2400rpm) and the engine was running as smooth as could be. No sign of that shaking.

I called an A&P friend and he said there was likely condensation in the tanks and the engine had sucked up a bit of water. I had borrowed a heated hangar to do my annual and the temp outside was about 25F, and the tanks were about half-full.

This seemed like a completely plausable explaination, so before I tear the cowl off I'd like to know if anyone else has other things (or other theories) I can inspect before I take her up again.

[crabandy]

Stuck exhaust valve?
Do you have EFIS engine data that you can reference?

[JackinMichigan]

Originally Posted by crabandy

Stuck exhaust valve?
Do you have EFIS engine data that you can reference?

Well, yes, but I didn't pay attention to it. From start to finish the whole episode lasted about 10 seconds.

[lr172]

Originally Posted by crabandy

Stuck exhaust valve?
Do you have EFIS engine data that you can reference?

Not very likely on an engine with around 75 hours. Op sig says he did 50 hour oil change in august of last year.

Larry

[lr172]

water is certainly possible. Is this a carb or FI. In 650 hours on my 6, I have never had a noticeable amount of water in my tanks and I am in similar weather patterns. I almost never top off the tanks before putting the plane in the hanger also. Further, cold air doesn't hold much moisture, so water from condensation would be much more likely or more severe in the summer. We haven't seen north of 40 in several weeks. If the air can't hold a lot of moisture, it can't come out in condensation.

It does sound like a fuel thing though. If you have efis logs, go back and look at your EGTs during the event and post the results. It can sometimes help narrow thinkgs down some. We want to know if it was system wide or limited to one or several cylinders. When it feels like the engine is shaking apart, that points to one or two cylinders going cold. Water in the fuel would behave like typical choking and sputtering, like when running a fuel tank dry; no serious shaking.

Assuming FI, If one EGT dropped to 0 during the event, pull the restrictor from the injector in that cylinder and look for debris and clean it out. A large chunk can fall into the hole, blocking fuel and then bounce around, leaving the hole open again, especially if you went to idle after the problem.

Larry

[BobTurner]

Did you sump the tanks prior to takeoff?

[F1R]

Annual inspection ... maybe have a look at your spark plug to wire end connections.

High probability of a human hands induced problem.
Check the B nuts or any joint in the fuel system that was inspected or worked on.

[Tim Lewis]

Originally Posted by JackinMichigan

Well, yes, but I didn't pay attention to it. From start to finish the whole episode lasted about 10 seconds.

Recommend downloading your engine data from the flight in question, upload to Savvy Analysis (free). Take a look at fuel flow, fuel pressure, EGTs, and CHTs at the time of the event. That way you can see if one cylinder was impacted, or all cylinders impacted.

[JackinMichigan]

Originally Posted by BobTurner

Did you sump the tanks prior to takeoff?

Yes, as part of my preflight. I usually only pull about a tablespoon of fuel from each wing and check for water. Didn't see any.

[Carl Froehlich]

I wonder if you have the ?bad vintage? of Champion spark plugs? I had six of twelve plugs fail in the first 300 hours - all high internal resistance.

Pull the plugs and verify center electrode is between 1000 and 4000 ohms. The six bad ones I had (new engine from Lycoming) were all in the 12,000 - 14,000 range.

High resistance plugs not only run bad, but they are very hard on your magnetos (or EI coils).

While your at it, check the spark plug lead resistance.

I replaced all the Champion plugs with Tempest - problem gone and while I no longer fly with aircraft plugs, I only recommend Tempest for those who do.

Do you have an EMS system that collects data? If so, reviewing EGT variations durning the rough engine period may tell a story.

Carl