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Need suggestions regarding my 231 turbo/engine


231LV

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Having posted a few times here, I have come to value the input from forum members. I'm currently experiencing a problem which, I suspect, is turbo related. Specifically, my critical altitude has dropped significantly. On a recent trip, I noted that I was running full throttle at 14k ft and producing 25 inches of mp. This is way down from my usual settings. I have noted over the last couple of years, a drop off in critical altitude (which used to be in the low 20's). It seems I am now relegated to not much higher than 15k ft. I am suspecting a turbo problem. I know it is still working as I feel the kick in the pants as I accelerate. I have a high time GB with a fixed waste gate and intercooler and asked my A/P mechanic to dial the waste gate in a bit just to see if I could recapture some of my lost altitude. It seems to have gotten worse. The waste gate (which is nothing but a threaded bolt) was in good shape and showed no evidence of breakdown. The plane is going in for annual in the next week or so but I am hoping some suggestions could save time and money in troubleshooting. Thanks, in advance

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1 hour ago, N231BN said:

Exhaust or induction leaks are typically the culprit if the turbo checks out. Perhaps a cracked intercooler?

On another note, the critical altitude with a fixed waste gate is supposed to be 14,500.

Thank for the suggestions and you are probably correct regarding critical altitude with the bolt but I have had the plane at 22k ft with four persons with the same bolt so something has changed and as we all know...watch the trend...

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  Critical altitude with "the bolt" (fixed waste gate) is usually between 13,800'-15,000' depending on the position of said bolt.  What this means is not that you can't go above 14,500', its that the engine can't maintain 100% power above 14,500'.  the 231 service ceiling is 24,000', so between 14,500' and 24,000' your Map should fall from ~29" to something that will only allow you to climb at 100'/min.

 

  Turbocharger turbine shaft looseness or an induction leak would be where I'd look.  @231LV, are you still getting 40" on takeoff roll and does the throttle seem to be pushed further in while doing so?

 

Ron

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Thank for the suggestions and you are probably correct regarding critical altitude with the bolt but I have had the plane at 22k ft with four persons with the same bolt so something has changed and as we all know...watch the trend...
There's no doubt something changed. Critical altitude is defined by the point the engine can no longer develop full power, the airplane still has a service ceiling of FL240.
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14 minutes ago, Marcopolo said:

  Critical altitude with "the bolt" (fixed waste gate) is usually between 13,800'-15,000' depending on the position of said bolt.  What this means is not that you can't go above 14,500', its that the engine can't maintain 100% power above 14,500'.  the 231 service ceiling is 24,000', so between 14,500' and 24,000' your Map should fall from ~29" to something that will only allow you to climb at 100'/min.

 

  Turbocharger turbine shaft looseness or an induction leak would be where I'd look.  @231LV, are you still getting 40" on takeoff roll and does the throttle seem to be pushed further in while doing so?

 

Ron

I have noticed that the throttle needs to be pushed in much further than ever before and yes, I am still getting mp in excess of 29 inches so the turbo is definitely working but I am suspecting a leak somewhere which is bleeding off some of the pressure that would otherwise go into the added charge in the engine....certainly, my mechanic will be inspecting the turbo for looseness, broken blades and other abnormalities. My use of the term critical altitude was not precise and I apologize to all for that since it has been correctly pointed out that my critical altitude is where it should be...what I meant to say was I can no longer climb as high as I once could before engine power peters out...

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@231LV,

 

  I was only pointing out the use of the term "critical altitude" for troubleshooting purposes so we were all on the same page.  It sounds like ~14k is now your service ceiling, which sucks.  If the throttle position difference on take-off is noticeable, as you say it is, then this would be a no-fly issue for me,  whether its an induction leak or a lose turbine shaft or whatever else, it could get much worse very quickly.  

 

  Please keep us informed on what's found and I hope it is as simple as a hose clamp or the over-boost valve not being fully seated.  You mentioned that you have an inter-cooler which adds a couple of extra hose connections to the system, more areas to check, good luck!

 

Ron

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At annual or when troubleshooting critical altitude issues I pressure check(~0.5psi)the intake system and exhaust system and spray with a solution of water a tiny bit of soap. Any intake and any reasonable exhaust leak will be a problem.  As mentioned above the intake hoses, pop off valve can leak and also the intake tube gaskets, upper deck lines, exhaust gaskets, slip joints(some leakage is normal), cracked exhaust, and turbo both sides.  Both Intake and exhaust leaks if large enough could show as a lose of critical altitude but exhaust leaks will be a blow torch at altitude and need to be fixed ASAP.  Also during the annual you would inspect the compressor blades and turbine blades and verify free rotation.  That should find your problem

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Got any JPI data?

losing some pressure to a single cylinder would be a funny non-descript feeling. But the data would be very clear what is happening.

Needing more throttle to obtain the same MP doesn't sound very comforting.  As in something has changed, and may not be stable.  It could change for the worse.

Do you have any Gami spread data to share?

Most unknown changes are not good.

Please share some data if you can.

On TC'd engines,

  • always check the exhaust system for exhaust leaks.  Worn and thinned exhaust tubes.
  • air intake system for air leaks. Loose hoses, intake seals.
  • Turbo oil system for carbon build up. Carbon build up from excess heat baking oil.
  • turbo vanes for whole vanes, not worn nubs.  Blade erosion from high TITs.

PP thoughts only, not even a turbo pilot...

Best regards,

-a-

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Thanks all for the thoughts and suggestions. I really appreciate them. I will be taking the plane in next week for annual. The shop is a quick 20 minute flight and since I just completed a 7 hour round trip flight, I am comfortable flying the plane. All engine analyzer data was normal...cylinder temps were in low 300's across the board, EGT also in mid 1500's...normal, oil pressure and temp normal...in short, the engine was working just fine....it simply ran out of power much lower than it used to. I'm betting that a pop off valve is opening at higher power settings or there is a pressure leak in one of the lines. I had my mechanic look at the turbo a couple of months ago because this has been going on for awhile now and it looked fine. I will keep everyone posted on the findings...

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OK....so I dropped the plane at the shop this am after a completely uneventful flight (everything looked fine on the analyzer)....first thing my mechanic found was a failed #1 jug....10 psi.....well, that would account for a low power problem....still waiting to hear what else he has found....

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Quick and decisive....

At least the mystery is out of the way...

I'm still guessing at more details... I expect that you may find an exhaust valve showing some problems...not being able to seal up properly...

Does your mechanic have a dental camera to send down the spark plug hole?

Or doing the compression test you hear air escaping through the exhaust pipe...

Best regards,

-a- 

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19 hours ago, 231LV said:

OK....so I dropped the plane at the shop this am after a completely uneventful flight (everything looked fine on the analyzer)....first thing my mechanic found was a failed #1 jug....10 psi.....well, that would account for a low power problem....still waiting to hear what else he has found....

One of the things many of us do, often as pre-flight check, is to turn the prop backwards through 2 complete revolutions. You should feel 6 compression strokes of similar resistance every 120 degrees of rotation. But in this case one of them would have had no resistance or a soft spot gap of about 240 degrees between more obvious compression strokes to alert you of the situation.  

Edited by kortopates
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1 hour ago, kortopates said:

One of the things many of us do, often as pre-flight check, is to turn the prop backwards through 2 complete revolutions. You should feel 6 compression strokes of similar resistance every 120 degrees of rotation. But in this case one of them would have had no resistance or a soft spot gap of about 240 degrees between more obvious compression strokes to alert you of the situation.  

Hi Kortopates,

Is a leaking exhaust valve a problem that Savvy analysis would be able to find?  I know from experance that a run up or in flight you may not notice low compression or a leaking exhaust valve. 

Jim F

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To bring an end to the adventure....only #1 was bad...the other 5 posted compressions of about 75 psi each. The oil cooler is cracked (accounting for more oil than usual on the belly) and my O2 bottle is timed out...filter was cut open and clean...otherwise, my mechanic says the engine looks pretty good.....I'm not going to replace the engine.....yet.....

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On 9/27/2017 at 12:53 PM, Jim F said:

Hi Kortopates,

Is a leaking exhaust valve a problem that Savvy analysis would be able to find?  I know from experance that a run up or in flight you may not notice low compression or a leaking exhaust valve. 

Jim F

Hi Jim,

Not really a leaky exhaust valve per se  but a burnt valve. Although once a valve is burnt, if its not leaking yet it will be very soon. Our FEVA software detects many burnt exhaust valve as it sticks while rotating, momentarily heating up, then cooling back down as rotation resumes. It creates a symmetrical signature that our software detects and alerts us. Unfortunately its not perfect, not all burnt exhaust valves exhibit the pattern. But we've also been able to save a number of exhaust valves with our maintenance clients that lap the valve in place when caught early enough to clean it up and stop the sticking. But even if we don't detect it early enough to save, its still much better detecting it before the cylinder swallows part of an exhaust valve!  Incidentally, I am not referring to "sticking"  as in sticking in the closed position as seen in a cold engine at startup (e.g., morning sickness) but sticking as the valve rotates as it open and closes as it is designed to do. 

Hope that answers your question.

Paul

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