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IO-360 engine stumble


HRM

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My money is on a fuel supply problem.  Sort of like using a hose that is too small.  At low demand the small hose works just fine but when you try to push a lot of water through, it restricts the flow to less than you need.

My guess is that at low power settings, that is, low MP, there is adequate fuel flow for the amount of air going to the engine and it works fine.  But when you push the power up, the number of air molecules getting to the cylinder drastically increases but the fuel flow is restricted.  It may increase some but not enough.  The mixture gets so lean that it can't burn and the cylinder dies.  Note that when your MP is at the highest, the fuel flow is only about 15 gph when it should be up around 18 or so.  Each cylinder should be using about 4.5 gph.  If your total is 15, that means #4 may only be getting 1.5 gph at full throttle.

If it was a mag timing issue it should affect all cylinders.

If it was anything prior to the distributor then it would also affect all of them.

I'd look at something inside the distributor blocking the flow, or the fuel line between the distributor and the injector, or the injector itself.  If you move injectors around and the problem persists with #4 then it's not the injector.

I would also second the suggestion to talk to Savvy.

Good luck.

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great data sharing, H!


1) Fuel supply is important... and a blocked injector may be what is happening... on #4.

2) The fuel / air ratio seems pretty wonky on the most effected cylinder... it starts pretty lean, then it goes too dry to fire...

3) #2 seems a touch drier, but not standing out in a big way at all...

4) was there a run-up in that data set anywhere?  

5) To best share run-up data it helps to hold the key for about 15-20 seconds in each mag position...

6) Usually a run-up leaves two distinct EGT peaks.... this is where mag health really shows up... the extra time is required because the data collection speed is 1-2 seconds at best... check your settings it might be set on 6 seconds...

7) If there were plug issues... the run-up really displays the plug health...

8) I think you have enough data to ask your mechanic if pulling and cleaning the fuel injectors is a good idea...

9) Really get a good look at the intake line with the precise flight line attached... if it has fallen off allowing that much air to get in that would be the aha moment....

10) a Good Dynon portable, and that precise flight device can go on the shelf in the home library.... :)
 

PP thoughts only, not a mechanic...

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At 16:35 MAP goes to 25.2 , FF stays around 6.4 and EGT 4 takes a nosedive.  Same thing at 18:28.  MAP 29.5 and FF seems low at 11.6.  Fuel pressure looks good enough and stayed above 22.    I believe fuel pressure is measured at the servo so I don't suspect  blocked fuel filters since the pressure stays up at full throttle.  This is easier to see using the live data than it is down below (time scales are not lined up exactly in the image below). 

Is this an RSA servo problem and #4 is the first cylinder to lean out and quit firing?  I'm scratching my head.  Hopefully someone can help solve the mystery. Sorry you are having problems but glad it didn't happen in-flight.

Merry Christmas HRM and MooneySpace!!

Capture2.thumb.JPG.cbe2c2af238c0d23993f98a46253feee.JPG

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Now that I have slept and thought about this following everyones comments, I am betting the bad boy here is #4.

Since only one cyl is wonky, this somewhat rules out the distributed subsystems (RSA, mags, manifolds, etc.).

Since this occurs only at TO power, if it happened in the air presumably there would be enough power for a lame wing landing. It is sort of a cool feature of the issue.

So now, as a very wise old A&P/IA told me once, back to fuel, air and spark at #4. I frankly think spark is fine.

Time to check the injector and for an induction leak, Merry Christmas all!

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25 minutes ago, HRM said:

Now that I have slept and thought about this following everyones comments, I am betting the bad boy here is #4.

Since only one cyl is wonky, this somewhat rules out the distributed subsystems (RSA, mags, manifolds, etc.).

Since this occurs only at TO power, if it happened in the air presumably there would be enough power for a lame wing landing. It is sort of a cool feature of the issue.

So now, as a very wise old A&P/IA told me once, back to fuel, air and spark at #4. I frankly think spark is fine.

Time to check the injector and for an induction leak, Merry Christmas all!

I think you are heading in the right direction with your thinking. An engine analyzer helps identify the problem area but doesn't always provide the direct cause. A good mechanic should be able to pinpoint the exact cause. I replaced a cylinder in September. My early warning sign was increased oil consumption. The engine monitor data looked fine. On the last flight before I flew in for maintenance, I did notice an anemic climb but otherwise my air speed was fine and I didn't see any other indicators on the engine analyzer. Turns out I had low compression on one cylinder caused by leaks at the rings and the exhaust valve. 

Merry Christmas and hope your problem gets resolved quickly.

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An interesting way for a cylinder to be working one minute, and not the next....

Valve not closing properly, or rings not seating...

A compression test and dental camera inspection would be interesting...

Rings don’t usually come and go.... they go... and don’t usually come back...

A valve not working, not rotating, ‘sticking’....

 

may be leaking enough to not have the compression needed for ignition...

 

Use caution,  when fuel doesn’t burn in the cylinder as expected.... excess fuel may be going towards the muffler where it may ignite and break something inside the muffler...

 

So...

  • air fuel ratio... seems to be a high probability....
  • air leaks into the intake line, usually become a smaller percentage as MP increases...
  • Sticky valve... something to look into if nothing else proves out...

 

PP thoughts only, not a mechanic...

Best regards,

-a-

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15 hours ago, carusoam said:

6) Usually a run-up leaves two distinct EGT peaks.... this is where mag health really shows up... the extra time is required because the data collection speed is 1-2 seconds at best... check your settings it might be set on 6 seconds...

I always run 1 second intervals. Memory bits are too cheap not to and the MVP-50 has a fairly huge flight data storage capability.

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18 hours ago, carusoam said:

Rings don’t usually come and go.... they go... and don’t usually come back...

There was discussion about freeing up stuck rings with various, not necessarily aviation specific, methods.  The one I remember reading about is using Mobil 1 automobile oil in the last hour or two before oil change to fix rings stuck due to flying too high for too long in a normally aspirated engine.

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19 hours ago, N201MKTurbo said:

You might have a broken valve spring. There are two on each valve. If one is broken there might not be enough tension to close it at high RPM. The valves have inertia and it takes more spring pressure to close them the faster they go.

I like that thought.  Probably easier to check than the fuel distributor too.

If a spring on the intake valve is broken it would allow the valve to stay open during part of the compression stroke so compression would suffer and so would power.

If a spring on the exhaust valve broke, the valve would stay open for a short time after the exhaust stroke and into the intake stroke.  That would reduce the partial vacuum created and reduce the amount of fuel/air mixture pulled into the cylinder.  That too would cause a reduced power output.

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1 hour ago, Yetti said:

baby jar test, clean injectors by soaking in Hoppes #9.   clean and rotate plugs while you are at it.  Report back.

Next step is to clean #4 in MEK and make sure the SVS is not leaking into the pipe.

This will take minimal cowling removal and be the simplest in terms of actual work. 

If this doesn't do it, the baby jar test will be next. Problem with it is that you really need two people to do it right. I let my A&P/IA off for X-mas :P

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7 hours ago, HRM said:

Next step is to clean #4 in MEK and make sure the SVS is not leaking into the pipe.

This will take minimal cowling removal and be the simplest in terms of actual work. 

If this doesn't do it, the baby jar test will be next. Problem with it is that you really need two people to do it right. I let my A&P/IA off for X-mas :P

Not really.  the baby jars sit up there pretty nice.   Just crank till the one you can see is half full.  Pulling the plugs first will help, if you were going to pull them anyways.

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10 minutes ago, Yetti said:

Not really.  the baby jars sit up there pretty nice.   Just crank till the one you can see is half full.  Pulling the plugs first will help, if you were going to pull them anyways.

Why crank with the plugs removed?  With the nozzles on the end of the lines and inserted into the jars, open the throttle and mixture then turn on the boost pump.

Clarence

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4 minutes ago, M20Doc said:

Why crank with the plugs removed?  With the nozzles on the end of the lines and inserted into the jars, open the throttle and mixture then turn on the boost pump.

Clarence

Which will work also.  Mechanical vs. electrical pump

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On 12/25/2019 at 10:13 AM, Yetti said:

Report back.

Yes, Sir.

Sorry, but I elected not to mess with the plugs. My concentrations were with #4 (see data plots) in regards to fuel and air, not spark.

We found the injector to be 'loose' in the sense that the ferule covering the filter screen was not secured by the fuel line connection. I took the injector home and let it bathe in acetone overnight. A check this morning show it to be clear of obstructions and I frankly think, since #4 was firing fine under low power demand, that there may have been an induction leak at the injector. Frankly, I am just guessing at this point.

I have my suspicions as to why this happened (two annuals ago!), but that is old news. I did not participate in that annual nor did my current A&P/IA.

So, the injector will go back on, although I plan to do the 'spray test' before installing it in the cylinder--correctly I might add. If this does not solve the issue then I will look to a possible induction leak, but I am feeling confident that 'this is it'.

It has been an education.

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15 minutes ago, HRM said:

Yes, Sir.

Sorry, but I elected not to mess with the plugs. My concentrations were with #4 (see data plots) in regards to fuel and air, not spark.

We found the injector to be 'loose' in the sense that the ferule covering the filter screen was not secured by the fuel line connection. I took the injector home and let it bathe in acetone overnight. A check this morning show it to be clear of obstructions and I frankly think, since #4 was firing fine under low power demand, that there may have been an induction leak at the injector. Frankly, I am just guessing at this point.

I have my suspicions as to why this happened (two annuals ago!), but that is old news. I did not participate in that annual nor did my current A&P/IA.

So, the injector will go back on, although I plan to do the 'spray test' before installing it in the cylinder--correctly I might add. If this does not solve the issue then I will look to a possible induction leak, but I am feeling confident that 'this is it'.

It has been an education.

I don't think you understand the value of reading the story a spark plug will tell. It will tell you if you are running lean or rich, or have an oil leak.   Like if plug in the other cylinders look normal and the spark Plug on #4 show lean, then you would not be guessing it was a clogged injector, you would actually know.

 

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21 hours ago, Yetti said:

The reason for using Hoppes #9 on injectors is because sometimes lead in the fuel is what clogs injectors.   Hoppes #9 is used for cleaning lead out of gun barrels.   See how that works.

I might suggest that you not leave it in Hoppes more than 15 minutes or so.  It will also clean the brass out of the injector.

 

Mark

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1 hour ago, markgrue said:

I might suggest that you not leave it in Hoppes more than 15 minutes or so.  It will also clean the brass out of the injector.

 

Mark

If this is true Mark, GAMI should caution people about using it on GAMInjectors.

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1 hour ago, markgrue said:

I might suggest that you not leave it in Hoppes more than 15 minutes or so.  It will also clean the brass out of the injector.

 

Mark

This is why I love MS!

I left that injector in acetone overnight. It emerged refreshed and renewed.

The folks at the local, somewhat redneck, Ace Hardware, knew nothing of Hobbes #9. I decided to stay the CB route, of which I am a charter member, and go with the el cheapo C3H6O.

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2 hours ago, markgrue said:

I might suggest that you not leave it in Hoppes more than 15 minutes or so.  It will also clean the brass out of the injector.

 

Mark

I’ve seen this before as well, if left too long brass particles appears in the Hopps.

Lycoming SL1275C details cleaning and reinstalling fuel nozzles.

https://www.lycoming.com/sites/default/files/Cleaning Fuel Injector Nozzles.pdf

Clarence

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FIXED!

So, for those of you following this and those who offered opinions as to what was wrong, here we go.

The consensus (including that of my A&P/IA) was that it was either an induction or injector issue on #4. After pulling all the cowling as well as the doghouse, I pulled the #4 injector and gave it the acetone spa treatment. I did notice that there were black particles floating in the  (CH3)2CO the next morning. I replaced the injector (don't worry, this is all under supervision while I work on my A&P merit badge) after getting a very positive baby bottle check (full throttle/MP squirting into a jar using the boost pump). I buttoned up the top and then I checked the intake pipe on #4 and was able to do the ‘click seat’ on it, which means that it had possibly loosened and was the source of the issue. Then I found the bolts on #2 ‘less than tight’ (can’t say they were loose). I read somewhere that those bolts can loosen over time. 

Having hit both the potential problem points, I put the lower cowls back on and proceeded to the full-power test. This was soooo satisfying as she went up to FP just like she should--no stumble!

All that is left is the flight test, and frankly, I think she's back. Oh, the data dump from the static test showed a 0.2 GAMI spread. Those two cylinders are dancing cheek-to-cheek now and 1 & 3 are keeping up with them.

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