TSIO360LB MP drop when leaned

[Pierre07]

Good afternoon all,

Question here since my mechanic and I have no clue what’s going on with this. I fly a 1981 231 with the TSIO360LB engine. When I get to cruise altitude, I adjust the power to 31/2450 and after couple minutes when everything settle, I pull the mixture to 9.8GPH and keep throttle and RPM the same as it was. On the last couple flights, it seems like couple minutes after I pull the mixture, all of a sudden, the MP starts dropping quick, like all the way to 25-26, as soon as this happens, I push the mixture back in and it goes straight back to where it was. I let it settle again and repull the mixture to 9.8 and then all is good for the entire flights (3-4hrs). It doesn’t always happen and when it happens, it’s not always the same time after I pull the mixture. And it never happens while running ROP, or it has never happened yet…

Did that or something like that ever happened to anyone here, I need help as we have no clue what can be going on.

Thank you very much in advance!!!

[Fly Boomer]

10 minutes ago, Pierre07 said:

Good afternoon all,

Question here since my mechanic and I have no clue what’s going on with this. I fly a 1981 231 with the TSIO360LB engine. When I get to cruise altitude, I adjust the power to 31/2450 and after couple minutes when everything settle, I pull the mixture to 9.8GPH and keep throttle and RPM the same as it was. On the last couple flights, it seems like couple minutes after I pull the mixture, all of a sudden, the MP starts dropping quick, like all the way to 25-26, as soon as this happens, I push the mixture back in and it goes straight back to where it was. I let it settle again and repull the mixture to 9.8 and then all is good for the entire flights (3-4hrs). It doesn’t always happen and when it happens, it’s not always the same time after I pull the mixture. And it never happens while running ROP, or it has never happened yet…

Did that or something like that ever happened to anyone here, I need help as we have no clue what can be going on.

Thank you very much in advance!!!

Fixed wastegate?

[jlunseth]

This is just a guess. At 31” I think your fuel flow of 9.8 is too low. The engine may find a way to stay alive for a little while but begins to be starved for fuel. You don’t say what fuel flow you push the mixture back in to, whether it is full rich or something else, but you are enriching the mixture and thus curing the fuel starvation.

A few things. First, it is not at all surprising that if you set a specific manifold pressure, say your 31”, and then you pull the fuel flow back that far, that the MP reduces with it. Actually, I am surprised it takes a couple of minutes. In the 231 there are a couple of things going on. First, there is an interlink mechanism that reduces or increases the fuel flow if you reduce or increase the MP. It is trying to keep the air/fuel ratio about the same as before you changed the MP. If I recall correctly, this is described in the POH. In my experience it also works in the other direction, that is, if you set MP and then reduce or increase the fuel flow, the MP will be varied with the reduction or increase in the fuel flow. So if you set 31” and then reduce the fuel flow from, say, full rich as far as 9.8 you should see the MP reduce with it. 

Second, remember that your engine is powered by a turbocharger that collects the exhaust gases and uses them to power a compressor fan. The more power the engine puts out the more compressed induction air the turbo puts out and vice versa, if the engine puts out less power the turbo will put out less compressed induction air. As the power from the engine reduces in response to your changing the fuel flow, the turbo is going to slow down and the MP is going to drop. 

What puzzles me a little is that, as you describe it, it takes a few minutes for this to happen. I am guessing the engine is finding itself starving for fuel, does ok for a little bit with the turbo is slowing, but then finds itself without enough fuel to stay alive.

Because of the interlink, there is always some fiddling with both the fuel and the MP knobs to get them where you want them. This is because changing either one of them changes the other, so you can’t just set the MP at 31 and expect it to stay there if you then reduce the fuel flow. In other engines, for example the 252, engines that fully automatic wastegate controllers, you can set the MP at a value and then reduce the fuel flow quite a bit without affecting you MP setting, but that is not how it works in the 231.

[Pierre07]

5 hours ago, jlunseth said:

This is just a guess. At 31” I think your fuel flow of 9.8 is too low. The engine may find a way to stay alive for a little while but begins to be starved for fuel. You don’t say what fuel flow you push the mixture back in to, whether it is full rich or something else, but you are enriching the mixture and thus curing the fuel starvation.

A few things. First, it is not at all surprising that if you set a specific manifold pressure, say your 31”, and then you pull the fuel flow back that far, that the MP reduces with it. Actually, I am surprised it takes a couple of minutes. In the 231 there are a couple of things going on. First, there is an interlink mechanism that reduces or increases the fuel flow if you reduce or increase the MP. It is trying to keep the air/fuel ratio about the same as before you changed the MP. If I recall correctly, this is described in the POH. In my experience it also works in the other direction, that is, if you set MP and then reduce or increase the fuel flow, the MP will be varied with the reduction or increase in the fuel flow. So if you set 31” and then reduce the fuel flow from, say, full rich as far as 9.8 you should see the MP reduce with it. 

Second, remember that your engine is powered by a turbocharger that collects the exhaust gases and uses them to power a compressor fan. The more power the engine puts out the more compressed induction air the turbo puts out and vice versa, if the engine puts out less power the turbo will put out less compressed induction air. As the power from the engine reduces in response to your changing the fuel flow, the turbo is going to slow down and the MP is going to drop. 

What puzzles me a little is that, as you describe it, it takes a few minutes for this to happen. I am guessing the engine is finding itself starving for fuel, does ok for a little bit with the turbo is slowing, but then finds itself without enough fuel to stay alive.

Because of the interlink, there is always some fiddling with both the fuel and the MP knobs to get them where you want them. This is because changing either one of them changes the other, so you can’t just set the MP at 31 and expect it to stay there if you then reduce the fuel flow. In other engines, for example the 252, engines that fully automatic wastegate controllers, you can set the MP at a value and then reduce the fuel flow quite a bit without affecting you MP setting, but that is not how it works in the 231.

Thanks Jlunseth

One thing I forgot to mention, when I drop the fuel flow to 9.8, I also adjust the Throttle at the same time to keep it at 31.

And when I push the mixture back in, I do it to full rich so about 14gph if I remember correctly.

The reason why I do 31/2450 and 9.8 is that it gives me 64% power and I can keep the CHT at around 370.

thanks!!

[Pierre07]

6 hours ago, Fly Boomer said:

Fixed wastegate?

No, I have the Merlyn Wastegate

thanks!!

[Z W]

That's a bit of an odd power setting to get to 65%.  The POH charts suggest you should be at 2350 RPM and 29.1" MP, 9.9 GPH (below). 

Personally, to get that flow, I find the engine is happier at 2500 RPM, 26" MP, and leaned to just under 10 GPH. Crack the cowl flaps as required to stay under 380 CHT which is very easy at the 65% setting.  You'll get about 130 KIAS at that setting, and cruse 145-170 KTAS or so, depending on altitude.

I've tried close to your setting as a recommended LOP cruise power setting.  It's generally suggested online as 2500 RPM, 32" MP, and lean to 10-11 GPH (about a gallon higher than you're using).  Never seen MP drop, but my engine has a noticeable intermittent stumble or burble you can feel in your feet, so I don't fly like that, even though the temperatures are good.

I think you're just running too lean for your power setting, resulting in loss of turbo pressure.  How many degrees lean of peak TIT are you when the power cuts out?

[hubcap]

According to the Continental Operators Manual for the TSIO-360-LB engine, the Maximum recommended RPM in cruise is 2450

[kortopates]

i am sure it’s too lean. 9.8 gph is indeed 64% power but probably with too much air. When you set up next time, keeping FF constant reduce MAP till your richest cyl peaks, then add the MAP slowly to determine just how LOP that richest cyl is. If it’s more than 15-25F LOP, cut back on the FF a bit to about 60% power, and lean to about 15F LOP and see how your temps are. If TIT is greater than 1600F you can lean a little more but might need to reduce FF a bit more.
A lower RPM will also help the engine to run deeper LOP.


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[Pierre07]

Thank you very much everyone, next time I fly I will try and see what it does and keep you posted.

Let's hope that's my problem, and other than my ego nothing will get affected haha

Thanks again!!!

[Z W]

20 hours ago, hubcap said:

According to the Continental Operators Manual for the TSIO-360-LB engine, the Maximum recommended RPM in cruise is 2450

That's interesting.  The POH I have, which was written for a TSIO-360-GB(4), does not contain that information, as best I can tell.  All it has are these "Cruise Power Schedules" that seem to imply you can cruise at any RPM from 2200 to 2700.

 

 

[Z W]

You're right though, here it is in the Continental Installation and Operation manual for the TSIO-360-LB:

 

Edited September 6, 2023 by Z W

[A64Pilot]

I don’t think many aren’t seeing what I think the issue is.

The issue as I understand it is that when this occurs, he enrichens it then re-leans to the same fuel flow and then MP doesn’t drop. So why did it the first time, but doing exactly the same thing it doesn’t the second time?

The “issue” should repeat the same every time, but he’s got something intermittent apparently

On 9/4/2023 at 10:03 PM, Pierre07 said:

I let it settle again and repull the mixture to 9.8 and then all is good for the entire flights (3-4hrs).

 

[A64Pilot]

5 hours ago, Z W said:

You're right though, here it is in the Continental Installation and Operation manual for the TSIO-360-LB:

 

I don’t have this engine and have never operated one.

I’ll point out though when you change one condition, not operating ROP for example, it may invalidate the other conditions.

It’s likely that the 160 HP is the limiting factor and if RPM and MP are the same, LOP usually produces less HP.

[kortopates]

A lot of good information is in the TCM Maintenance and Operations manual that’s not in the POH - from power settings to starting methods. Recommended for every owner.

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[Pierre07]

5 hours ago, A64Pilot said:

I don’t think many aren’t seeing what I think the issue is.

The issue as I understand it is that when this occurs, he enrichens it then re-leans to the same fuel flow and then MP doesn’t drop. So why did it the first time, but doing exactly the same thing it doesn’t the second time?

The “issue” should repeat the same every time, but he’s got something intermittent apparently

 

Thanks a lot A64Pilot, yes it’s exactly my problem, if it always did it, I would have known and tried something else but the fact that it always do it the first time when it does and it’s never right after I lean it.

And I have never been able to do it after leaning it the second time with the same exact specs blows my mind.

This kinda tells me it’s not a air/fuel ratio problem otherwise it would do it everysingle time once I bring it to 9.8GPH.

I’m still going to change the MP and RPM next time to be in a better place but would really like to know if it’s another problem.

Thanks!!

[A64Pilot]

Frankly it’s over my head anything I could come up with like a sticking fuel servo would actually be just a guess.

I think however you need to treat this seriously and find an engine expert, because she’s talking to you, letting you know something is on its way out, that’s my belief anyway. Many thing seem to give off warning signs before they fail.

Maybe this post will bump this to the top and someone can at least give you info on who to take it to.

[Pierre07]

Good afternoon all,

update on my problem, we OH'd the fuel pump couple months ago, problem is still happening.

I tried 3-4 different power settings to see if it was that, and still happening as soon as I run it LOP (about 10-20deg LOP), but again only the first time I lean it, then good for the rest of the flight after I re set it to the same exact settings the second time.

Still always no problem if I run it ROP.

Do anyone know someone who deals with TSIO-360 all the time that may have an idea what to do with that.

Whatever it is, it needs to be fixed, but nobody know where to start and I don't want to just change parts and hope it's the right one...

Thank you very much again!!!

[kortopates]

You could upload some of your EDM-900 data with the issue to SavvyAviation after you re-set the sampling rate to every 1 sec from the default of every 6 sec and I can take a look. Open a free account on Savvy and better yet fly the Savvy Test profile here: Savvy-Flight-Test-Profile-Expanded.pdf (savvyaviation.com) 

But my guess is that your exceeding the engine's limits on how lean it can go smoothly due to either mixture distribution or ignition.  Does it have gami injectors that have been tuned to ensure a distribution of <= 0.5 GPH?