Engine trouble M20C?

[Techsan02]

I have a question as a brand new Mooney pilot. I have lurked on the site for quite some time and learned some valuable information. Real quick, I currently fly a M20C with the Johnson Bar, and have all of about 10 hours in this airplane so I am still learning it. Unfortunately, a search of the forum didn't yield my answer.

Last night I took a short 39nm trip to another airport and back. On the way back during my descent (of all about 1500 ft.) I began to feel what I can only describe as a "pulsating" coming from the engine. It is not what I consider "roughness". All of my engine instruments were in the green and I was not losing RPM's. Visually everything looked perfect. I will thing happening at night made it even more worrisome. I made it back no problems and when I got on the ground did a quick run-up and no issues. It seemed like a loss of power the way it felt, but nothing showed that to be the case. RPM was around 2300 in the green and MP maybe around 18". This happened quickly mind you as I started the descent. As I got close to entering the pattern I applied full prop and the "pulsating" continued. 

I hope with this limited information maybe someone can point me in the right direction. I will probably have someone look at it, but thought I would see what possibly is going on. 

[isaacpr7]

I don't know if it's related to your issue but mine used to do the same thing when I lowered the MP for approaches. I replaced the spark plugs, shower of sparks, and overhauled the magnetos and the issue went away for good. Some of the items I fixed were because they were due or for another reason but one of those fixed the problem.

Sent from my SAMSUNG-SM-G930A using Tapatalk

[Hank]

I always descend at cruise power in my C, then back off the throttle to slow down for the pattern. It's not uncommon to get some burbling on final, especially when I go to idle for the last couple of hundred feet. I've always thought of it as the "blub blub blub" sound of lots of power waiting to be unleashed.

Unless yours is doing something else? I've never felt any pulsating, just the blubber and burble of the engine at or near idle power. Kind of like a hot rod, but with much less power. More speed, though! 

[N201MKTurbo]

Try playing with your mixture, it is ok to lean the mixture as long as you remember to richen it up if you need to go around.

[Hank]

P.S.--as I descend, I periodically reduce throttle and richenot mixture to maintain the cruise values of MPH and EGT. Otherwise, both will rise to undesirable values. 

[takair]

Are "C"s prone to carb ice?  What are the symptoms?  Do you have carb heat applied?

[Mcoyne34]

Every carb is prone to carb ice given the correct conditions. 

 

Symptoms: Reduced power and rough running engine and a drop in manifold pressure. Fixed pitch planes would show a drop in RPM  

 

I always run carb heat periodically during cruise and set it during pre landing checklist on downwind. I always turn carb heat off on short final just in case I need to go around. 

Edited July 2, 2016 by Mcoyne34

[Techsan02]

Thank you for the replies. I did have carb heat on starting at the beginning of my descent and mixture rich. I have never noticed this, and it was about every 30-45 seconds and short in durations. No vibration but more of a pulsating or surge. It was just eye opening because I hadn't noticed it yet in flight. 

Just had the right mag fixed due to the last guy who obviously did not know what he was doing. Possibly need mag overhaul or spark plugs. 

Edited July 2, 2016 by Techsan02

[ArtVandelay]

Did you download engine monitor data and look for any anomalies?

[DXB]

Could this be some kind of prop balance and/or resonance issue? It sounds like  an  rpm setting alone is not enough to get it- but perhaps a particular pitch/rpm/MP combination?  just thinking aloud- I am just a PP, and a green one at that...good luck!

[bonal]

Welcome techsan I was thinking if this might be prop governor related did you notice an oil pressure fluxuation as the engine was oscillating. I'm likely way off base but what you describe does not sound like an ignition or carburetor issue.

[Hank]

It could also have been engine auto roughness, those noises you only hear at night and/or over water.

[Andy95W]

Lean aggressively anytime you're below 65% power, especially taxi and descent.  Also try different rpm.  Mine doesn't like 2300 very much.  Depending on its mood usually 2350-2450 is smoother.

[Patto]

Congrats on your new purchase!  I am also a very new Mooney owner.  I purchased a 1974 M20C three weeks ago today.  I owned a Cessna 150 many years ago.  This is NOT a Cessna 150! 

When I ferried my M20 home from California, during my descent I noticed the engine seemed to be running rough.  Just every few seconds sounded like a cylinder missed or something.  I've noticed it now during several descents.  Carb heat does not resolve it.  Leaning helps but doesn't stop it completely.  While anything odd, especially with the engine, worries me there does not seem to actually be anything wrong.  

I don't know if that sounds similar to what you're experiencing.

[3914N]

Maybe similar to Patto, my 'G seems to be running a little rough, but I can't really figure out if it's in my head or not.  I'm down for annual at the end of the month, so I'm hoping that some plug cleaning and mag re-timing may help the issue (or at least get it out of my head).  It will be interesting to see what the compressions are as well.

One thought.  My engine does NOT like to be run full-rich with the carb heat on.  The result is pretty extreme roughness as the mixture is just way too rich.  I'd recommend playing with your mixture in the descent to see if that affects the problem.  Please keep us posted.

[Htwjr]

My C would run rough if I applied carb heat with the mixture full rich on descent and landing.  I asked about it early on as well.  Now I land with it leaned and have no problems.

[Techsan02]

Thanks for the continued replies. I did not have any fluctuations in oil pressure. But I did have mixture full rich with carb heat on. I also was not familiar of the night problems with auto engine roughness. I hope that's not common knowledge cause I can't say I've heard of it. It's good to know others have experienced it and it seems to be nothing major! Great responses!!

[carusoam]

Also...  Check your procedures for carb heat during landing.

It is often used with other carbed engines.  The side effect is increased richening of the mixture.

There is a discussion around here of people that use or don't use carb heat during landing.

A carb temp sensor is an important add on feature if you are getting an engine monitor.  Also good for a stand alone gauge if you don't get a monitor this year.

Best regards,

-a-

[Hector]

I'm one of those that do not use carb heat. Right or wrong in five years and close to 500 hours in my C I have experienced carb icing once and it was in cruise. I live in north Florida and it's plenty humid and there are times of the year when the conditions are perfect for carb icing, and yet, my plane does not seem to be very susceptible to carb icing at all. I have an engine monitor so I'll probably add a carb sensor at some point but it's just one of those things that has had little to no effect in my plane. On descent to landing my mixture stays leaned and it goes to rich only after I enter the pattern.