Wastegate, controller? Loosing manifold pressure M20K ‘87

[MooneyMark]

Unfortunately I’m in need of your ideas again. My 1987 M20K 252 with just over 1000 hours total time is grounded for over five weeks now. It had some work done on the turbo due to the oil leaking from the exhaust. Nothing was replaced overhauled or repaired, save a few clamps. She flew fine for a few hours but she sits in the warm hangar of the maintenanceshop again. Take-off with full power and 36” MAP but just in to the climb the MAP drops to about 26” at WOT. What has been done? The turbo has been looked at and checked out okay, the output of the engine is okay, but the waste gate doesn’t seem to close. The controller and wastegate were shipped to Main Turbo for evaluation, the controller was out of spec and overhauled, the wastegate itself checked out okay but was overhauled anyway.  Back on the engine, after some adjustments it seems to check out, but after a testflight yesterday we seem to be back at square one. I get full power at take-off but it drops off after rotation. Up in the air I tried different powersettings but did nog get more than 26”. That wastegate is not closing. I guess heat could have something to do with it? I tried another take-off after landing but had to reject it. I’ve read up on the subject with some of the great articles from Mike Busch (who doesn’t respond to e-mail BTW), six weeks ago I didn’t know what a controller was... do you guys have any thoughts?

[Guest]

Any loose clamps in the induction system?  Continental recommends leak checking the induction and exhaust systems with the pressure side of a clean vacuum cleaner.

Clarence

[Awful_Charlie]

Does the engine actually lose power when the MAP gauge shows the reduction? If not, I would suspect some fluid in the MP line that manages to block the line when in the nose up attitude. I'm not familiar with the Continental turbo controller setup, but if it was on my lycoming I'd be tempted to check all the controller/wastegate/feed/control/scavenge hoses for kinks/blockages or maybe purging for air

Edited March 11, 2018 by Awful_Charlie

[N231BN]

Do you notice a drop in oil pressure at the same time?

[jackn]

Just a thought, the overboost regulator, the big can on the engine’s right side may be defective, thereby opening at 26”. 

 

[jlunseth]

Pretty hard to diagnose over the Internet, but I have two thoughts, and I have to preface it by saying I am not a mechanic nor do I fly a 252 ( I have a 231), so take my comments for what they are worth.

It sounds to me as though you have a wastegate control failure, the question is whether it is the wastegate or the controller.  It sounds more like thecontroller to me.  It  sounds as though, when heat builds up after a period of operation, something is happening in the controller.  But just in case, I would have your mechanic perform a long full power maintenance run-up on the ground, long enough to create the heat build-up.  If the MP falls, then you know it is the heat build-up.  This would rule out that any altitude change on take-off is causing it.  I suppose its possible an ambient pressure change is causing something to happen in the controller, but not likely, so I would just do the run-up to rule it out.  If the MP does not fall during the run-up, then it is going to be some kind of pressure sensing issue.

After that, there are two possibilities in mind.  One, as I understand it the controller is hydraulically operated (pressurized engine oil, I think), so it could be something in the hydraulic system, a valve or control gate of some kind.  It could also be purely physical binding of the wastegate due to heat expansion.  But I don't think the second possibility is it.  Unless you are doing something with the MP, prop, or fuel controls at the point where this happens, if the gate itself is binding, one would think it would just stick where it is, i.e. closed or mostly closed, and you would have full power but would have difficulty reducing power.  So it sounds to me like it has to be something in the controller or the hydraulic system that causes hydraulic pressure to the wastegate to fall, in turn allowing the wastegate to open when the engine gets hot.   That's all I can think of at the moment. 

[carusoam]

MS ideas from things I have read, not actual experience.

Sounds like a waste gate getting stuck and not controlling...

The annual maintenance includes lubricating certain parts of the turbo control with something renamed mouse milk.  A high Temperature lubricant used on exhaust systems.

Check with your mechanic to see if this type of lubricant has been used during the annual.  Does it need to be used again with some parts cleaning?

It could be that oil has entered the exhaust system and turned into crusty carbon in some locations. This could be preventing movement of the waste gate...

Pure speculation on my part. Somebody posted the diagrams of a mooney wastegate control system around here somewhere... PP thoughts only, not a mechanic.

Best regards,

-a-

[kortopates]

An instantaneous drop to ambient air pressure suggest a huge induction leak. The fact that it comes and goes points to the overboost valve popping open prematurely. Check that since it can cause your symptoms.


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[N231BN]

It could be the turbocharger bearing as well.

[MooneyMark]

On ‎11‎-‎03‎-‎2018 at 12:46 PM, Awful_Charlie said:

Does the engine actually lose power when the MAP gauge shows the reduction? If not, I would suspect some fluid in the MP line that manages to block the line when in the nose up attitude. I'm not familiar with the Continental turbo controller setup, but if it was on my lycoming I'd be tempted to check all the controller/wastegate/feed/control/scavenge hoses for kinks/blockages or maybe purging for air

Yes it does, you don't get any 'kick' from the turbocharger, that usualy makes it's presence know around the 27". But I do guess the fault lies somewhere hidden in a hose or linkage. All the components themselves check out fine.

[MooneyMark]

On ‎11‎-‎03‎-‎2018 at 8:38 PM, N231BN said:

It could be the turbocharger bearing as well.

When the waste gate is closed manually, the engine makes full power. The turbo itself is not at fault. There is something wrong between controller and wastegate, I guess...

[MooneyMark]

On ‎11‎-‎03‎-‎2018 at 1:37 PM, N231BN said:

Do you notice a drop in oil pressure at the same time?

Can't say that I did. I did a trial run yesterday and now the wastegate remained open, so I had to reject the take-off. I was suspecting that may be with a colder engine/engine-oil I might get the same results as I did Saturday (36" take-off and then a reduction to 25/26" WOT), but the wastegate remains open all the time now.

[MooneyMark]

On ‎11‎-‎03‎-‎2018 at 4:50 PM, jackn said:

Just a thought, the overboost regulator, the big can on the engine’s right side may be defective, thereby opening at 26”. 

 

I guess with the overboost regulator you mean the wastegate? If not, please tell me more.

[MooneyMark]

On ‎11‎-‎03‎-‎2018 at 8:06 PM, carusoam said:

MS ideas from things I have read, not actual experience.

Sounds like a waste gate getting stuck and not controlling...

The annual maintenance includes lubricating certain parts of the turbo control with something renamed mouse milk.  A high Temperature lubricant used on exhaust systems.

Check with your mechanic to see if this type of lubricant has been used during the annual.  Does it need to be used again with some parts cleaning?

It could be that oil has entered the exhaust system and turned into crusty carbon in some locations. This could be preventing movement of the waste gate...

Pure speculation on my part. Somebody posted the diagrams of a mooney wastegate control system around here somewhere... PP thoughts only, not a mechanic.

Best regards,

-a-

Thanks again for you input, the wastegate moves freely and without any problems. It has been overhauled along with the controller by Main Turbo, the controller was sent back even, and replaced with another item. Great service from Main Turbo! My mechanic wil be on the telephone with Gary (Main) today, I hope he can shed some light on the matter.

I've been doing some of my IR training now on a C172 now and that just isn't 'it'.

[jackn]

47 minutes ago, MooneyMark said:

I guess with the overboost regulator you mean the wastegate? If not, please tell me more.

No. The overboost (valve/ regulator) is the can on the top of the engine on the right. It is attached to the induction system. On your engine it will open at 37". This could explain why you initially got full power, but it opened and failed to reseat. It's possible that once you shut down and let it sit, the valve reseated, but it is clearly still faulty.

 

[MooneyMark]

13 minutes ago, jackn said:

No. The overboost (valve/ regulator) is the can on the top of the engine on the right. It is attached to the induction system. On your engine it will open at 37". This could explain why you initially got full power, but it opened and failed to reseat. It's possible that once you shut down and let it sit, the valve reseated, but it is clearly still faulty.

 

Thanks Jack, I'll check in to that!

[exM20K]

your shop should have or should be able to make a cover to replace the overboost valve.  Fly with it removed, and see if it is the malfunctioning piece.  The symptoms sound like it is, and it's a lot cheaper than removing and shipping out wastegate/controller.

[MooneyMark]

6 minutes ago, exM20K said:

...and it's a lot cheaper than removing and shipping out wastegate/controller.

Well, that ship has sailed... It has already become very costly.  I've asked my shop to check the O/B valve out. But is there an overboost valve on a automatic wastegate system? Guarding against overboost, Isn't this the work of the wastegate?

[exM20K]

6 minutes ago, MooneyMark said:

Well, that ship has sailed... It has already become very costly.  I've asked my shop to check the O/B valve out. But is there an overboost valve on a automatic wastegate system? Guarding against overboost, Isn't this the work of the wastegate?

yes.  it's commonly called a "pop-off" valve.  it's a cylindrical piece about 3" x1" towards the end of the induction system.  It's there as an emergency measure on most every turbo'd engine.

[MooneyMark]

Thanks!

[ziggysanchez]

An overhaul of those components does not guarantee that they were repaired properly. I had a problem with my 231 where the MP would drift. It would increase slowly at first and then pretty quickly as MP increased. My wastegate was sent off for overhaul and came back with the same issue. When I spoke to Merlyn they acknowledged that when they bench tested it there was a pin hole leak in the bellows but it was within spec so they didn't replace it during the overhaul. I sent it back again for repair and the second time it came back fixed. I would question what was replaced at overhaul.

[MooneyMark]

3 hours ago, exM20K said:

yes.  it's commonly called a "pop-off" valve.  it's a cylindrical piece about 3" x1" towards the end of the induction system.  It's there as an emergency measure on most every turbo'd engine.

He has added it to his list of possible causes. But he said they hardly break... 

[kortopates]

He has added it to his list of possible causes. But he said they hardly break... 

All true, but they do fail and I see that’s what@jackn and I tried to suggest back in post 5& 8.
Symptoms really point to it and it’s easy enough to test.


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[MooneyMark]

If it can break, it will at some point! I’ll keep you posted, thank you all for your input

[Cardinal767]

The waste gate is spring loaded open and has to have oil pressure to close it. The controller releases that oil pressure when it needs the gate to open. Cap the line going from the waste gate to the controller and the waste gate should close. A pressure gauge instead a cap on the line can tell you if there is oil pressure down stream of the waste gate and upstream of the controller.