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power loss on takeoff when cold M20K 231 Turbo


Aspen2013

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When taking off below 40 degrees F I have fuel flow increase to 30 gph and MP climbing past redline. Engine shudders when fuel flow is that high probably due to over rich situation. This is a turbo charged 231 with fixed waste gate and intercooler. Max MP is 37. Any ideas. I believe to be the fuel divider or fuel pump. Engine was properly warmed before take off. Does well after 2 to 3 cyles of this issue.

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I am not sure I understand why there is an issue since you have to manually keep from overboosting with less throttle. Its should not be all the way forward but whatever it takes to make 37". Gently keep advancing till you have near 37" without overboosting. If you are trying to do that, I suspect you are advancing it too quickly. Also make sure oil temp is over 100F and cyl CHTs are 250F or higher before going to full power.

Edit - BTW from your description when you say MAP went over redline I assume you are saying MAP went over 40" which is what is causing your excessive FF. How high did MAP and FF go? Did you look at your downloaded engine data yet? Although your max FF may simply need adjustment, it sounds more like engine is just overboosting from too much throttle - but I may not be understanding your description correctly. 

Edited by kortopates
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Getting the FF set-up properly can be importantant...

30gph is high even for an IO550 at SL at WOT...

We have recently had a report of a K losing power during the T/O run...

Finding that thread may require somebody with a stronger memory or search skills than mine...

Has the fuel system been maintained at all lately? @M20Doc has posted a few pics and procedures for this engine...

Best regards,

-a-

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Everything you are stating is correct. I always monitor MP and keep it below redline. (this aircraft has intercooler so max is 37" without is 40") The fuel flow is usually around 22 gph on climbout.  This usually is the norm no problems at all.  For some reason once winter starts to hit and I travel places and it is cold I have the problem. This is what happens. I do everything exactly the same as any other day however, shortly after lift off the MP pressure starts to climb out of control with fuel flow going to 30 gph. I have to be quick on reducing the throttle as the engine also starts stumbling. Once the throttle is reduce MP pressure may now be 25 so I increase it slowly and it is all going well until the whole cycle repeats itself.  I really try to keep the MP around 32" and continue a climb. Usually this happens 2-3 times before the issue goes away. The rest of the flight is back to normal. The take off temps seem to be below 40 degrees when this happens. The aircraft is hangared and an engine heater is used. The CHT's are always above 250 before taking off.  I believe something is happening with the fuel divider or pump.  Could it be the fuel divider has some mechanism inside it that sticks when it is cold? Perhaps going to max fuel flow causing MP pressure to go up until an over rich condition develops causing the engine roughness?  The fuel pump is new as of Mar 2017. Fuel divider unkown time in service. A lot of data was supplied by JPI to see what is happening.

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Fuel flow and MAP are related so when your map rises the fuel pump senses this and increases output.  Is it possible that you have an induction from a loose coupling which seals as the engine warms up in the climb?

I would pressure check the induction system and the exhaust system as a starting point.

Clarence

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11 hours ago, Aspen2013 said:

I really try to keep the MP around 32" and continue a climb. Usually this happens 2-3 times before the issue goes away.

A couple of questions to help in trouble shooting.

1.) Are you still climbing when the issue goes away?     

2.) How is fuel flow being determined?    Actual flow measured via a Shadlin, JPI, etc... or is this flow being derived by fuel pressure at the divider. 

If you had engine monitor data, Paul or Clarence would have already solved this.

Bill

 

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My K does something similar on every flight but it only happens while I'm in cruise and OAT doesn't seem to be a contributing factor. While in cruise (running LOP) my MAP will "runaway" and I have to make adjustments usually to keep TIT out of the red. It's not as abrupt as what happens to yours. My MAP seems to drift slowly at first but once it gets started it begins to move up fairly quickly. I have the Merlyn waste gate but no intercooler. We sent the waste gate for overhaul and it seemed to improve but I still have the issue. No induction leaks were found. I'm interested to find out what is causing your issue. Maybe it will give me an idea of where I should look next.

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My K does something similar on every flight but it only happens while I'm in cruise and OAT doesn't seem to be a contributing factor. While in cruise (running LOP) my MAP will "runaway" and I have to make adjustments usually to keep TIT out of the red. It's not as abrupt as what happens to yours. My MAP seems to drift slowly at first but once it gets started it begins to move up fairly quickly. I have the Merlyn waste gate but no intercooler. We sent the waste gate for overhaul and it seemed to improve but I still have the issue. No induction leaks were found. I'm interested to find out what is causing your issue. Maybe it will give me an idea of where I should look next.
What you are experiencing is normal for a fixed or differential wastegate(merlyn) turbocharged engine when operating LOP. It is referred to as bootstrapping. It is a completely different issue than what the OP is experiencing, at least the cause is different.

Any excessive bootstrapping when ROP is a cause for concern.
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2 hours ago, N231BN said:

What you are experiencing is normal for a fixed or differential wastegate(merlyn) turbocharged engine when operating LOP. It is referred to as bootstrapping. It is a completely different issue than what the OP is experiencing, at least the cause is different.

Any excessive bootstrapping when ROP is a cause for concern.

I appreciate your insight. Thanks.

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What you are experiencing is normal for a fixed or differential wastegate(merlyn) turbocharged engine when operating LOP. It is referred to as bootstrapping. It is a completely different issue than what the OP is experiencing, at least the cause is different.

 

Any excessive bootstrapping when ROP is a cause for concern.

Technically bootstrapping is when the turbo can no longer maintain the target Upper Deck Pressure at the current altitude and current RPM and MAP fluctuations begin to occur. It's easy to confirm by increasing RPM by another 100 rpm and the bootstrapping will cease till climbing higher.

 

Even without looking at his data, I am pretty sure what is causing [mention=15449]ziggysanchez[/mention] issue is running too deaply LOP for either the ignition system or mixture distribution. This typically leads to some misfire in the leaner cyl, which raises EGT and TIT and sets off a positive Feedback loop with the turbo spinning faster from the hotter exhaust, raising MAP and increasing FF as a result which reinforces higher MAP till the pilot fixed it. But yes, without a real controller, the pilot will need to fix it with adjustments to the controls. Diagnostic data would be required to tell if mixture distribution or the ignition system is driving it. But it could also be that the engine is being operated deeper LOP than necessary for the % power.

 

 

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Technically bootstrapping is when the turbo can no longer maintain the target Upper Deck Pressure at the current altitude and current RPM and MAP fluctuations begin to occur. It's easy to confirm by increasing RPM by another 100 rpm and the bootstrapping will cease till climbing higher.
 
Even without looking at his data, I am pretty sure what is causing [mention=15449]ziggysanchez[/mention] issue is running too deaply LOP for either the ignition system or mixture distribution. This typically leads to some misfire in the leaner cyl, which raises EGT and TIT and sets off a positive Feedback loop with the turbo spinning faster from the hotter exhaust, raising MAP and increasing FF as a result which reinforces higher MAP till the pilot fixed it. But yes, without a real controller, the pilot will need to fix it with adjustments to the controls. Diagnostic data would be required to tell if mixture distribution or the ignition system is driving it. But it could also be that the engine is being operated deeper LOP than necessary for the % power.
 
 
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I may have used the wrong term but a fixed wastegate engine, when run LOP, behaves very similar to a variable-absolute pressure wastegate engine when above critical altitude. Once you are LOP, any change in MP(or mass airflow) results in a change in FF and vice versa.

My 231 behaves the same as ziggysanchez's, I believe the cause is the mixture control slowly increases due to vibration and after I set my LOP cruise power, any increase in FF creates a chain reaction which results in the engine running about 85% power at near peak TIT if you let it get there.

It has behaved this way ever since I replaced the fuel pump, I think the old pump had a stiff diaphragm in the Android which made it less sensitive to changes in UDP.
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I may have used the wrong term but a fixed wastegate engine, when run LOP, behaves very similar to a variable-absolute pressure wastegate engine when above critical altitude. Once you are LOP, any change in MP(or mass airflow) results in a change in FF and vice versa.

My 231 behaves the same as ziggysanchez's, I believe the cause is the mixture control slowly increases due to vibration and after I set my LOP cruise power, any increase in FF creates a chain reaction which results in the engine running about 85% power at near peak TIT if you let it get there.

It has behaved this way ever since I replaced the fuel pump, I think the old pump had a stiff diaphragm in the Android which made it less sensitive to changes in UDP.

I certainly agree with you there that any increase in air or fuel causes this positive feedback loop to reinforce it. But make sure it isn't being triggered by some misfire for the reasons I mentioned. I see it a lot and deeper you go LOP, the more sensitive you are to this since power is beginning to drop off quickly. If I recall correctly, you're a client of ours so don't hesitate to send create to send an analysis request and I'd be happy to help you look at it. But include it with some Savvy test profile data so we can check both mixture and ignition. What your describing seems a bit severe for changes I would consider are pretty normal for a manual wastegate. Anyway don't hesitate to send in some data.
There was some changes to the latest fuel pump configuration if you got your part no on it updated as well to the latest configuration. They added a galley that now allows fuel to pass through at ICO, unlike prior configurations, affecting the previous recommend method of circulating hot fuel with the pump at ICO for hot starts - now you have to be careful not to flood the engine using that technique.


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  • 3 weeks later...

I'm not a 231 owner, but flew with a friend today in a 231 with a new engine and intercooler (don't know about the wastegate) and the owner was trying to not go over 36" on takeoff.  I was amazed to see at least three finger widths of throttle remaining at 36" and over the course of 6 full stops and takeoffs noticed at least a couple momentary over boosts to 43" and one just past 45".  Two questions.  With that much throttle remaining, is the throttle out of rig and can the waste gate be adjusted to max at 40 or so? Thanks.

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I don't know the finer details of the aircraft turbo systems, though I understand the supercharging cycle well.  Is the wastegate actuator hydraulic, using pressurized engine oil?  Or are they purely some simple spring and diaphragm mechanism?  

I would be happy with a link that describes the function of the Continental Turbo engine controls with Merlyn wastegate.

Just the thoughts of a normally aspirated pilot, not an A&P :-) 

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1 hour ago, Cayman44 said:

I'm not a 231 owner, but flew with a friend today in a 231 with a new engine and intercooler (don't know about the wastegate) and the owner was trying to not go over 36" on takeoff.  I was amazed to see at least three finger widths of throttle remaining at 36" and over the course of 6 full stops and takeoffs noticed at least a couple momentary over boosts to 43" and one just past 45".  Two questions.  With that much throttle remaining, is the throttle out of rig and can the waste gate be adjusted to max at 40 or so? Thanks.

Lots of throttle remaining is normal for that airplane. Sounds like he needs to add throttle MUCH more slowly if he blew past his intended target  by 10".

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12 hours ago, Cayman44 said:

Two questions.  With that much throttle remaining, is the throttle out of rig and can the waste gate be adjusted to max at 40 or so?

  If the engine idles at ~650-750rpm then the throttle is not out of rig.  The 231 has a fixed/very little adjustment available waste gate, without the Merlyn the adjustment can only be made on the ground and adjusted to the wide open position I can still get 45" at Sea Level, but my critical altitude is lowered considerably.  I usually roll in to 32"-33" to start take-off roll and that puts me at about 37"-38" at take-off speed.  I do not have an inter-cooler so my max continuous manifold pressure is 40".

 

Ron

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