Engine surge / hiccup during flight?

[AlexLev]

Was at 6,000 cruising above the clouds with fields that were LIFR below when my engine hiccuped. Things just felt like they vibrated and it almost powered down (not fully, maybe a 300rpm loss if I had to quantify it, but I wasn't looking at RPM needle at that exact moment) and up super quick (all within a second). It happened so quick that I didn't notice any signs with CHTs or EGTs beforehand.

My passenger seemed to notice it too, so I don't think it was just me. Everything purred for the rest of the flight and I was just flying back from having my inboard fuel screws sealed on the right wing from maintenance (but I was on the left tank when it happened).

Any clues on what to investigate? I was on edge for the rest of the flight since with the 300OVC fields below me, my only plan would have been to assume best glide and aim toward a road on a map and hope to break out and land it. Not great odds. I have a carburated Mooney, engine just overhauled about 1year and 200hours ago. I imagine it could have been a little bit of water that may have been hiding in the tanks, at least that's what I'm telling myself.

 

Edited May 2, 2019 by AlexLev

[Guitarmaster]

I had this happen just the other day. It hiccuped fast enough it didn’t even show up on the engine monitor.

After it happened, I decided to do an in-flight mag check and found that one of the plugs was fouled. With the engine monitor watching it was very easy to pick out the bottom number six plug.
When I did this check, it would stop running on that cylinder then it would clear out and would run again.

After doing a clean and gap on the plug, no problem.


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[Oldguy]

39 minutes ago, Guitarmaster said:

After it happened, I decided to do an in-flight mag check and found that one of the plugs was fouled. With the engine monitor watching it was very easy to pick out the bottom number six plug.
When I did this check, it would stop running on that cylinder then it would clear out and would run again.

To the OP: If you have an engine monitor, I would suggest running the Savvyanalysis.com flight test profiles to get an overall stress test of your engine and then load it up to their site. Even the free service lets you look in detail at the results from the tests, and if you were to load some screen shots up here, I feel certain you would have more recommendations than you can imagine.

[DXB]

Plugs are a good place to start, but a single plug fouling shouldn’t be easily perceptible in terms engine operation unless ignition off the  other plug on the same cylinder is weak or the timing is off between the two mags. In flight, a single nonfunctional  plug may show up on the engine monitor as a slight decrease in CHT and a higher than usual EGT on that cylinder - at least it did for me, and a subsequent in flight mag check proved which plug it was.  Im not sure what your problem was, but I’d certainly investigate further.  A close look at the engine monitor recording before, during, and after the event seems warranted.  A fuel  pressure and fuel flow recording would also be of interest if available on the monitor.

[AlexLev]

Unfortunately, my engine monitor is an older one which does display all 4 EGTs and CHTs digitally, but no download functionality. I'll investigate the plug. Is there a fuel filter or something to look through? How accessible is it? I'm curious if in the process of the shop resealing the inboard screws -- some goop could have gotten into the tank?

Edited May 2, 2019 by AlexLev

[smwash02]

I'd check the usual items mentioned above, but it sounds like classic carburetor icing to me. Harder to feel the onset with a constant speed until it really flares up.

The conditions were good for it based on what you're describing and being at the altitude you were.

 

[AlexLev]

I turned carb heat on after the event for a bit. My carb temp gauge was in the yellow (close 0-5C) at the time of incident, OAT was about 45-50F, but I was above clouds in clear air at time of incident.

Edited May 2, 2019 by AlexLev

[TTaylor]

I would check the plugs, but I am +1 on the carb ice.  A chunk of ice ingested would have the effect you describe.  Sounds like you were in the correct temperature range to produce ice.

[Yetti]

My fuel injected did that on take off.   One of the plugs lost it's center electrode.   Start with plugs.

[DXB]

3 hours ago, smwash02 said:

I'd check the usual items mentioned above, but it sounds like classic carburetor icing to me. Harder to feel the onset with a constant speed until it really flares up.

The conditions were good for it based on what you're describing and being at the altitude you were.

 

Good point- hope it was that

[jaylw314]

3 hours ago, AlexLev said:

I turned carb heat on after the event for a bit. My carb temp gauge was in the yellow (close 0-5C) at the time of incident, OAT was about 45-50F, but I was above clouds in clear air at time of incident.

Remember carb icing is still possible without visible moisture outside.

[FloridaMan]

That always seems to happen when flying over unfavorable terrain or open water. My strategy for engine failure over a cloud deck would be to come through it with as much energy as possible to use to navigate to my landing site. 

[Hank]

47 minutes ago, FloridaMan said:

That always seems to happen when flying over unfavorable terrain or open water. 

My first experience with auto-rough was when Palm Beach vectored me over the Everglades at 4000msl on my way to FXE. Turned out to be Com2, set for FXE ATIS with the volume low, just starting to break squelch . . . . But it did worry me until I figured it out!

[FloridaMan]

19 minutes ago, Hank said:

My first experience with auto-rough was when Palm Beach vectored me over the Everglades at 4000msl on my way to FXE. Turned out to be Com2, set for FXE ATIS with the volume low, just starting to break squelch . . . . But it did worry me until I figured it out!

4000ft? They like to send me over the glades so low I can smell them. 

[Hank]

1 hour ago, FloridaMan said:

4000ft? They like to send me over the glades so low I can smell them. 

At some point they descended me to 2000msl and vectored me 8nm over the Atlantic before turning inbound on the ILS. Just don't remember where . . . .

[carusoam]

Drops in engine power....

Without an engine monitor data bank to go back to...

We get to review the three key things that produce a fire...

1) Fuel... any drops of water could cause this... sump the tanks, drain the fuel sep...

2) Air... anything blocking the air supply? Or living behind the air filter?

3) Ignition... spark plug check, magneto check...

4) Below the clouds has high RH... above the clouds usually has lower RH... without knowing the actual RH, the carb temp indicator is the way to go... the modern engine monitor would have the data to go back to...

Updating to a new/used different engine monitor has been approved...  

Best regards,

-a-

[RobertGary1]

I agree that it’s not a plug. I’ve had plugs die in flight and the only way you can tell is on the EDM. The drop in power isn’t enough to cause a 50rpm difference. Even if you lost an entire mag you’d only get a 50-100 rpm drop momentarily. 

More likely you sucked up a bit of ice that melted or perhaps a fuel interruption 

wouldnt hurt to do a wobble test either  

 

-Robert 

Edited May 12, 2019 by RobertGary1