Emergency Landing..Looking for some answers

[Alexdangelo]

Hi All...Had an interesting one this weekend. Was 4 hours into a 4.5 hour CC from S. Fla to near Charlotte NC. Flight and Wx were perfect the whole flight. I was in cruise at 9500, when all of a sudden I had a power loss, slight vibration and some very angry noises coming out of the motor. I was in the startle effect, as this came out of nowhere, for probably 10 seconds. I hit the boost bump, switched the tanks, checked throttle ,mixture and mags and all were as they should be. The issue continued and after about 30 seconds I decided I didn't know what was happening and I wasn't about to find out if the engine was in the mood to eat itself!!!  I pulled the power to idle and made an emergency landing to an airport about 10 miles away. The landing was uneventful and the engine never quit, so I was able to taxi out. 

 

After about 20 minutes, I went back to inspect for anything obvious, leaking oil,  metal on dipstick, odd smells or sounds and all was normal. I started it back up, ran it up and it was totally normal. As the AP on the local filed was gone for the day, I left the plane there. Spoke to him the next morning, he ran a compression check and all was in the high 70s, plugs looked brand new and ran up fine for him as well. 

Spoke to my local AP and this gentlemen in SC and the consensus was a stuck valve. 

 

I was able to get back to the plane to download the engine data from the flight. The first image shows that everything was normal, and then it gets messy. The other image is the exact moment of the "event". You can see that the EGT on Cly 1 drops off a cliff. I know the scale is not on this image, but the EGT1 dropped about 450 degrees in 5 seconds.

 

Does a "stuck valve" in flight represent like this, has anyone else experienced this and what is the fix. I am getting a few different opinions from the 2 APs, but curious what the Mooney brain trust here thinks...

 

Thanks All

 

 

 

 

 

 

 

[IvanP]

Could also be clogged injector or fuel servo/spider issue. While partially clogged injector would tend to rise EGT if running ROP, it will casue drop in EGT if you run LOP. Completely obstructed injector will cause the cylinder to go cold. Were you running ROP or LOP at the time of the incident?

[dkkim73]

I think stuck exhaust valve should increase EGT(??). Stick intake valve would starve combustion... But i don't think it happens often (?)

Hard obstruction of an injector might explain it. Partial obstruction would run lean, might give higher EGT but hopefully an AP will weigh in with what's most common. 

Clean plug might be false negative if crud burned off during your run up. 

Did he borescope it? 

 

[N201MKTurbo]

One EGT went down, but the rest went up. This indicates that one mag went offline. You said you checked the mags, did you cycle them? How did it run on the individual mags? Or was the rise caused by you switching mags?

It would help if we knew what kind of plane you have.

[hazek]

5 hours ago, N201MKTurbo said:

One EGT went down, but the rest went up. This indicates that one mag went offline.

This actually indicates plugged air bleed of the injector:

https://precisionairmotive.com/wp-content/uploads/2019/06/15-812_b.pdf

[N201MKTurbo]

1 minute ago, hazek said:

This actually indicates plugged air bleed of the injector:

https://precisionairmotive.com/wp-content/uploads/2019/06/15-812_b.pdf

Not three at the same time.

[hazek]

A plugged air bleed in this range allows the exit of the fuel restrictor to be exposed to manifold suction, which effectively increases the pressure differential across the restrictor and causes an increase in fuel flow through that nozzle. Since this nozzle is now, in effect, stealing fuel from the other nozzles (injector servo output flow will remain the same) this cylinder will run rich and the other cylinders will be correspondingly lean.

 

I read this as yes, three at the same time.

[hazek]

11 hours ago, Alexdangelo said:

You can see that the EGT on Cly 1 drops off a cliff

Important point is that it did not drop to 0. This means combustion was still ongoing however under a very rich mixture. I had a similar experience on takeoff last year. Revving sounds from the engine, temps all over the place, reducing power brought it back to manageable for an immediate uneventful landing. On inspection nothing was found, on ground run nothing was found and this was my engine data:

[PT20J]

I had this happen twice. It ran rough for a few seconds and then cleared up. Data looked like yours.  I believe it was a momentary partial restriction of a nozzle. It The last time it happened I noticed excessive fuel stains around the affected nozzle afterward which might indicate fuel was being forced out the air bleed hole instead of going into the manifold.

 

[Wingover]

Had the same and it was a blocked injector.  EGT will never drop to zero unless the outside temp is 0c or below.  I stuck valve in the closed position will increase EGT and since your compression is good, it can't be stuck in the open position.

If you are really worried about a valve than boroscop the cyl but I would clean the injector. 

[Bartman]

I had a mag die in flight once.  All EGT increased by over 100 across the board, and there was no roughness.  A stuck exhaust valve would allow combustion gases into the exhaust and increase EGT. That is not what you are describing and that's not what I see on the screenshot.  This appears to be a partially clogged injector to me.  I had that happen once right after I had my JPI installed and right over an airport.  I circled down, taxi to the shop, and asked them to clean the single injector.  After a test flight around the pattern, I completed the remainder of my 4-hour flight that afternoon.

Under IA supervision, I just cleaned all four injectors at the annual inspection using Hoppes #9 and a basic ultrasonic cleaner.  Using knowledge from previous threads on this website, I used a water bath in the ultrasonic cleaner and put the injector and the restrictor in separate baggies into the water.  I ran it a couple of times and used fresh Hoppes #9 each time.  I did them one injector at a time, and they were returned to the same cylinder.  

In 2020, all injectors were cleaned, and my EGTs all changed nearly simultaneously in transition to LOP.  That drifted over time until the GAMI spread reached 0.6 in 2024, and you could feel a slight vibration while in LOP.  Now I'm back to simultaneous EGT transition and zero vibration LOP.

[Andy95W]

3 hours ago, Bartman said:

.  A stuck exhaust valve would allow combustion gases into the exhaust and increase EGT.

Not true.  A stuck exhaust valve would result in no compression in that cylinder, and the fuel/air mixture would not ignite.  EGT would drop significantly. 

[hazek]

6 hours ago, Andy95W said:

EGT would drop significantly

Wouldn't the mixture ignite in the hot exhaust causing the EGT to rise dramatically?

[Andy95W]

1 hour ago, hazek said:

Wouldn't the mixture ignite in the hot exhaust causing the EGT to rise dramatically?

No.  The amount of fuel per cycle is actually very small, but when coupled with compression and a well-timed spark it burns very efficiently and produces power and heat.  Again, if there is no compression the small amount of fuel just isn’t sufficient to sustain combustion.  I suppose once it reached the point in the exhaust that the other cylinders’ exhausts met, it would probably burn there- but that point is well past the location where the EGT probe lives.

Additional proof: if you do a magneto check with a fouled plug, that cylinder’s EGT will drop to zero, even though fuel is passing through the cylinder.

[PT20J]

I fully understand (and generally agree with) the argument that much preventative maintenance unnecessarily risks maintenance-induced failure for little benefit. However, after experiencing two inflight events that appear to be due to partially clogged nozzles, I have resumed cleaning the nozzles during annual inspection. Avgas leaves behind a varnish as it evaporates and avgas does not have the detergents that are present in mogas. 

[hazek]

11 hours ago, Andy95W said:

Additional proof: if you do a magneto check with a fouled plug, that cylinder’s EGT will drop to zero, even though fuel is passing through the cylinder.

Very good point! Thanks.