Strange incident - partial engine failure, then a few days later engine seems fine

[hazek]

So last Friday I had a partial engine failure shortly after takeoff. I experienced slight revving of the engine and the TIT was above redline (1800°+) until I reduced power. I was correctly configured. I managed to land just fine and right afterward doing the runup cylinder nr 5 was cold on either both, R or L magneto.

The plane was looked over and no issues were found. They did a borescope of nr 5 and found some scratch marks but apparently nothing to be concerned about. The scratch marks are on the wall on one side and are small, an inch in length maybe. Other than that nothing else was found, they turned the engine on and a full power runup was just fine.

Anyone have any ideas?

Also what are the correct fuel flow and TIT during full power? I think FF increased since the last annual (2 flight hours ago) where the 34y old original boost pump was replaced with a new one. Also when the engine is shutdown, MAP under-reads 1.2 inHg  compared to ambient pressure.

Would be very grateful for any ideas.

Edited August 7 by hazek

[EricJ]

Clogged injector on #5?    Sometimes they clear themselves, so it'd be hard to say for certain.

 

[Fritz1]

FF on my engine is 29-30 gph on takeoff, think this is about right, MP is 35.5 to 36.5" depending on temperature, there is a table in the service manual showing max permissible MP over induction air temperature, the induction manifold has a treaded receiver for an IAT probe, then you can read IAT and monitor density controller, under normal circumstances you will not go below 35.5" and not above 37"

[FoxMike]

1800TIT on takeoff or in any other phase of flight indicates a problem.  Detonation a possibility or just too lean a mixture.  My TIT on Takeoff is not over 1400.  First thing is to think back and make sure you taxied into position for takeoff with a full rich mixture.  When I am taxiing I lean the mixture and before moving onto  the runwayI lean some more.  The idea is if I apply power without going full rich the engine will quit  before I do damage.  At full rich and takeoff power your TIT needs to e in the 1300-1400 range.  

[hazek]

When it happened I verified mixture was rich and it was. I even flipped on the boost pump even though at full power it was already running and I changed the fuel tank.

I am not 100% but I think fuel flow at full power increased after the annual inspection 2 flight hours ago when the boost pump was changed. Can this happen somehow in connection with changing the boost pump?

I'm completely lost what to do here. We're now looking at the manifold pressure gauge because it under-read the ambient pressure when the engine is shut down. But I can't help but have this feeling this is a red herring and something else is wrong.

[kortopates]

Do you have an engine monitor?

The only thing that can cause such a high TIT is lean mixture assuming it’s corroborated by high EGTs.


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[hazek]

Is it possible to have a lean mixture due to some fault or obstruction of the fuel system but the Hoskins FT-101A fuel flow metter showing a higher than usual fuel flow?

Edited August 8 by hazek

[kortopates]

Absolutely, see @EricJ post #2


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[hazek]

17 hours ago, Fritz1 said:

FF on my engine is 29-30 gph on takeoff,

According to the engine manual it should be 27.5gal/h. Confirmed to me by Lycoming tech support when I called today.

[kortopates]

27.5 is actually a bit low, 29-30 is much better. We have the same issue with Continentals where the manufacturer has the max fuel spec on fuel low side.

Regardless though this wouldn’t be your issue nor would MAP gauge; especially when it affected a single cylinder.

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[hazek]

The thing is before the boost pump was changed I thought it was 27.something gal/h. Unfortunately I can't remember precisely and have no record of it but this is what my memory says.

 

But how could a blockage lead to the FT-101A fuel flow meter show too high fuel flow?

[FoxMike]

One other thought I had is the possibility of contaminated fuel.  You might want to take a fuel sample and have it tested.  Talk to some other pilots and see if they have had any problems.  

[kortopates]

….
But how could a blockage lead to the FT-101A fuel flow meter show too high fuel flow?

An injector blockage would be a partial blockage to that one cylinder. It only takes a small fraction of the total fuel to that cylinder to make it very lean and push up the temps. A blockage large enough to stop combustion is unheard of but kill the one cylinder with its EGT going cold and TIT dropping from the other cylinders having a richer than normal mixture.
With any injector blockage, the fuel pump and servo are still delivering the full amount of fuel but to the other cylinder.


Fuel contamination in the form of water would cause a drop in EGT and TIT, not an increase. As well as a rough engine.
If there was a large amount of water in the fuel it would kill the engine before you got off the runway.


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[FoxMike]

I was thinking a small amount of jet fuel or low octane gasoline. 

[hazek]

I refueled before taking a 35min flight to the airfield where the incident happened. Then the plane sat outside for 1.5h in 23°C sunny weather. Fuel contamination with water or other fuel is extremely unlikely, especially from that fueling station and given the course of events.

Coming back to the fuel flow. Can it be something reading erroneously too high while it's actually lower than normal?

[kortopates]

12 hours ago, hazek said:

I refueled before taking a 35min flight to the airfield where the incident happened. Then the plane sat outside for 1.5h in 23°C sunny weather. Fuel contamination with water or other fuel is extremely unlikely, especially from that fueling station and given the course of events.

Coming back to the fuel flow. Can it be something reading erroneously too high while it's actually lower than normal?

You need to provide more details to get helpful advice. So far all we've heard is the TIT got over redline and above 1800F, and that Cyl 5 went cold after the event when you did a mag check. But as far as the event you've only shared the high TIT and "slight revving" (don't know what that means).

Besides the TIT being high, was the only high EGT issue with  the Cyl 5? Do you know if the event was limited to just the one cyl, #5? This is what I assumed since you borescope check focused on #5. Do you know what your EGTs and CHTs where during the event? Do you have an engine monitor you can download data from?  What have they checked besides borescope the #5?

I assume this is a very new to you aircraft and perhaps your first experience with a fuel injected engine.

12 hours ago, hazek said:

Can it be something reading erroneously too high while it's actually lower than normal?

Such a broad statement is not answerable.

[Fritz1]

I concur, there may be several issues at play, Rheinland Airservice is a MSC, Aeromecchanica in Switzerland does a fair amount of Mooney work, then there is Mastenbroek in the Netherlands and a new one, MAS in Leutkirch Germany. One of these shops will be able to help. This may be frustrating to the OP right now, but getting to know a new airplane and fixing all the squaks just takes time, persistence will eventually prevail

[Fly Boomer]

1 minute ago, Fritz1 said:

getting to know a new airplane and fixing all the squaks just takes time, persistence

And lots of money. 

[hazek]

So I finally managed to get the EDM data and here's what we can see:

 

Goes to show how shit human memory is. It was actually nr 4 EGT that went above 1800, TIT went nearly to 1700, and nr 2 EGT was erratic and dropped. Also Nr 4 CHT acted unusual as well as nr 2 CHT. Anyone has any ideas? So far borescope of all cylinders hasn't revealed anything.

[hazek]

A test of the fuel injectors revealed nothing, they all delivered about the same amount of fuel into jars in the same span of time. Stiff rubber air manifold hoses connected to the nozzles were found and replaced. One of them had a slight crack.

[Rick Junkin]

3 hours ago, hazek said:

One of them had a slight crack.

Do you know what cylinder the cracked one was on? Could help explain the #4 and #2 behavior.

[hazek]

Unfortunately no, I don't. But they now replaced all of them. I'm really starting to believe everything is fine and I just had a blocked injector until the fuel pressure was high that resolved itself once the fuel pressure was lowered. Nothing at all was found wrong with the engine.

[Shadrach]

On 8/8/2024 at 3:03 PM, hazek said:

According to the engine manual it should be 27.5gal/h. Confirmed to me by Lycoming tech support when I called today.

That number is a minimum and is likely suboptimal for cooling.

[hazek]

12 hours ago, Shadrach said:

That number is a minimum and is likely suboptimal for cooling.

I do admit I'm exactly sure what the graph that number is from represents, especially not because it has "Lean limit" written in the middle.

It's from here:

[hazek]

But anyway fuel flow number is now a moot point. I have the EDM data and can see the EGTs and TIT that we had before the Weldon boost pump was replaced so I have a baseline for how rich or lean the engine should be running when at take off power set. We're set to fly again in a few days and so those will be my numbers that I want to see to know if fuel is flowing correctly.