Temporary Rough Engine At Cruise

[Hawth200]

Yesterday, while cruising at 6500', my carbureted O-360 started running very rough (like I had lost one cylinder) and I noticed that the single cylinder EGT indicator was indicating about 100 degrees higher than normal. The CHT was indicating normal. I figured that the mixture setting had become overly lean, so I began to enrichen the mixture.

 

The change in mixture made no difference in the rough running engine and strangely the EGT indicator did not react to the change in mixture. The fuel pressure was normal. I did not switch either magneto off, but decided to next apply carb heat to see what effect that would make. With carb heat applied, the engine began to stumble even worse and did not clear up. From that, I figured that I now must be running an overly rich mixture setting.

 

I began to lean the mixture back out ignoring the EGT indicator that was still reading about 100 degrees high. As I leaned the mixture the engine began to run smoothly again. I kept my eye on the EGT indicator. It continued to read 100 degrees high for a few minutes before settling back to normal. The engine operated normally for the rest of the flight (about 40 mins). While it felt like an eternity, the roughness probably didn't last more than 3 or 4 minutes.

 

I'm just trying to come up with a reasonable explanation for this. My first thought was that I may have experienced a sticky exhaust valve...  

 

I just thought I would mention it here to see if anyone had any possible explanations.

 

 

Thanks!

 

 

Seth

 

 

[flyboy]

Seth,

 

    Glad to know that you made it on the ground OK. How long did you run the carb heat?

[Hawth200]

I didn't run carb heat very long. Probably no more than 10-15 seconds. I noticed no change in MP

[1964-M20E]

Could have been a plug.  I had a similar incident whit my E noticed one of the EGTs was higher than normal.  Turned out to be something on the plug but it cleared itself and the return flight and run-up was without any problems.

[Hawth200]

I suppose that's a possibility. I just find it hard to believe that a plug could load up like that with a cruise power setting about 1.5 hours into the flight. All of my plug fouling experiences have been from idling on the ground. I guess it could happen though. In hind sight, I wish I would have done a mag check.  It sure was rough!

 

If it had continued much longer I would have landed ASAP

[Wakeup]

To follow up... Would you check the mags the same way you do on the ground before run up ? Thanks Troy

[Hawth200]

Troy,

 

Yes, I could have done an in flight mag check, much like you do during your typical run-up on the ground.

 

I did do a quick run-up when I got on the ground before shut down and everything checked normal.

[pinerunner]

I wonder that no one seems to be considering the possibility you might have had carburator ice.  Running rough and then even rougher upon application of carburator heat sounds like the classic description. If droplets of water were getting into the combustion process it might have slowed the combustion down so that there was still some burning going on when it went to exhaust, making the EGT go up. I'm winging it a bit here but why not check out more details on carburator ice?

[carusoam]

How do you feal about a four channel engine monitor?

You have clearly found an issue.

But, without data there is not much else to do but guess...

Seeing the EGT rise is telling something...

Was it a plug going away on that cylinder?

Could be a magneto going away on four cylinders?

With a decent engine monitor you could point to the cylinder that is being challenged.

Add an extra thermocouple to know if carb ice is the challenge...

My C experienced carb icing once in ten years. Low altitude, high moisture day under low clouds (possible, but low probability)

Sticking valves are a bit more serious. I had one stuck in the C, the shaft got bent. A stuck valve is a land Now kind of situation. The engine is fighting 3 vs. 1 while trying to fly... There may not be enough excess power to maintain altitude.

Seriously consider the monitor.

Good luck,

-a-

Hope this helps

[Mooneymite]

I wonder that no one seems to be considering the possibility you might have had carburator ice.  Running rough and then even rougher upon application of carburator heat sounds like the classic description. If droplets of water were getting into the combustion process it might have slowed the combustion down so that there was still some burning going on when it went to exhaust, making the EGT go up. I'm winging it a bit here but why not check out more details on carburator ice?

 

Absolutely!  Classic carb ice scenario.

 

From FAA Flying Tips - P-8740-24:

 

Pilot response to warning signs should be:

 

• Apply full carb heat immediately (may run rough initially for short time while ice melts)

All those folks who say they've never experienced carb ice with their O-360 need to add one word:  "Yet".

[flyboy]

I wonder that no one seems to be considering the possibility you might have had carburator ice.  Running rough and then even rougher upon application of carburator heat sounds like the classic description. If droplets of water were getting into the combustion process it might have slowed the combustion down so that there was still some burning going on when it went to exhaust, making the EGT go up. I'm winging it a bit here but why not check out more details on carburator ice?

That's what I was thinking when I asked how long he ran the carb heat. That would explain the rougher running with carb heat but I would have stayed with the carb heat for at least one or two minutes. I have only had carb ice in my mooney once that I know of, it was in heavy rain and while IMC. Carb heat made it run worse until the ice melted away. I did notice a slight loss of manifold pressure prior to the rough running.

[Hank]

Sounds like carb ice to me, too. Do you have a carb temp gage? I find mine to be very useful. No carb ice yet, but I've had the carb temp in the orange stripe when in-and-out of the clouds, and I pulled enough carb heat to be >5C above the stripe.

Melting carb ice will make the engine stumble even worse as it melts. Did you notice a drop in manifold pressure? That's another sign of carb ice.

[Hawth200]

The relative humidity wasn't all that high, but the carb temp was in the caution range. I probably should have kept with the carb heat a bit longer, but the EGT through me for a loop. I wouldn't expect high EGT to be a symptom of carb ice.

 

An engine analyzer is definitely on my wish list... I would have loved to been able to see what all the cylinders were doing.

 

 

Thanks for all the comments, I love this forum!

[Hawth200]

I did not notice a drop in MP.

[N201MKTurbo]

A fowled plug on cylinder three would cause the problem you describe. When one plug stops firing the EGT will rise. When you leaned it out the plug started firing again. When you did your ground run up it was working ok, you said it smoothed back out. Next time check your mags in flight. It is the first thing you should do. If it runs smooth on one mag then run on that mag and periodically check the other side by going to both to see if it has cleared itself. It doesn't do your engine any good to run on both when L or R is smoother.

I have talked to other mechanics who are amazed that pilots will fly for hours on both instead of turning off the bad mag. That is what the key is for....

[Hawth200]

Yeah, the ignition switch would have been the thing that I tried next. Next time, if I encounter it again, I will definitely handle it differently. 

[Hawth200]

I didn't mention it, but I was also flying through some pretty moderate turbulence at the time, some of the worst i have ever encountered... So I had my hands full, it sure makes it difficult to sort through issues when you're being thrown around. But, as pilots that's what we are trained to do...

 

I was flying from Greensboro, NC back home to Ohio. I knew it wasn't going to be a pleasant flight over the mountains because of the winds yesterday afternoon, but I didn't think it would be that bad.  

[flyboy]

You made it back down without damaging anything or anybody. The airplane can be used again.   Well done. It can be difficult to think about turning mags off or keeping that carb heat on that seems to make things worse. Having passenger(s) aboard greatly compounds the problem. You have now had some time to think about the event and to be better prepared if it should happen again. That's what I call a successful flight.

[Hank]

I've made the flight over Greensboro many times, but I'm barely in Ohio at HTW. Where are you based, Hawth?

[Hawth200]

Hank, 

 

I'm based out of KHOC, Hillsboro. Not all that far from you. Actually, this event happened just south of Huntington, WV. That's where I would have landed if I would have needed to.

[Hank]

Hillsboro was supposed to have been on my student long XC, but I changed to Flemington, KY to avoid having to replan everything if the MOA was hot that day. I have a friend in Columbus who gets lost every time she drives to Hillsboro . . .

 

I'm busy moving south, but there's a cookout at HTW on the 17th. I am going to try to be there--come on down! [with apologies to Bob Barker] I need to post the flyer here in an appropriate spot.

 

P.S.--we're the little strip across the river from HTS, but we've been known to shoot an approach into HTS then come over Special VFR, it's literally 4 nm to the NE. Child's play when approaching 30, the normal runway there. Like you, I have the factory single-point everything, plus an obviously later "optional carb temp gage" calibrated in Celsius; it makes a good match for my OAT in Fahrenheit.

[Wakeup]

Newbie wanting clarification after a few tequila shots... I have never heard of running the engine on one mag if running rough. I would have thought it would need both for the engine to run at peak performance. Thanks Troy

[Hank]

Nah, that's why there are two mags. One can fail, and the engine will keep running. Each mag powers one spark plug in each cylinder, so cutting one mag off will slightly increase the burn time, which will slightly decrease power. But if it's smooth, take what you get, go home and get it repaired.

[carusoam]

From my C152 experience...

Goofy thought process of a young pilot....

(1) rough run-up at a really remote airport.

(2) depart with rough running plane to nearby airport with the hope of finding mechanical assistance. It gets dark.

(3) stay the night at local hotel. Plan the next steps.

(4) following day, rough mag has turned into a dead mag..

(5) hell, it has two mags...

(6) training says, that's why we have two mags...so it must be OK to do this.???

Looking back on that experience...

Power may be greatly reduced on a single mag. Especially if fuel is still burning after the exhaust valve....(showing up on the EGT is a hint)

On a single mag, Max altitude was less than 2,000'. Normally 12,000’...

Climbing to 2k' took a really long time.

Take-off distance was equally impaired.

It was a school plane that had undergone recent maintenance.

It didn't have a JPI either.

What killed the first mag was unknown. I stopped to see if it had departed without me...

Without knowing why the first one is misbehaving...

Why would the second one be any better?

Fortunately our Mooneys aren't school planes. But...

Thanks for letting me share.

Best regards,

-a-

.

[M204ever]

There should be a drop in MP with carb heat applied, except for the carb heat was already unintentionally on (bad sealing in carb heat system).

This circumstance may lead to higher EGT as well.