Manifold Pressure Fluctuation TSIO360-MB

[231MJ]

Need some ideas.  On the last few flights, about 30 minutes into the flight the manifold pressure starts to fluctuate by about 1-2"  of pressure.  It's really disconcerting...I've had it start in the climb and at cruse.  Changing the MP by a few inches (from climb to cruse) does not fix it.  Changing the RPM from climb to cruse does not fix it.  It does go away after a while.  Good thing is it's annual time and I'll go through it with the IA but was hoping I might get some ideas from the gang.  Where should we start?

Thanks,

August

[carusoam]

Start with what MP gauge are you using?

Is it the old mechanical gauge with the engineered weep hole behind it?

Or is the power actually drifting?

If this is the case, it is an aluminum tube that is prone to loose connections or possibly a problem around the weep hole.  The older Mooney's had a smaller line that was more prone to failure of the line because of vibration and movement...  My C's line broke at the calibrated weep hole...

It is impossible to set Power, ROP, without an accurate MP gauge...

Best regards,

-a-

 

Edited January 22, 2017 by carusoam

[milotron]

Does it bounce around or just drift? My vernier throttle cable is a little loose and will turn by itself changing manifold pressure on me. If I don't pay attention, it has moved that much in the past. There is a method to snug this up, but I haven't got around to it yet.

[231MJ]

Thanks for the quick response.

This is a 1979 K with an up-dated MB engine.  The MP gauge is the old mechanical version.  

The MP does bounce up and down in fairly rapid oscillation. The power surges and then drops and surges again.  That's what's so troubling.  

[carusoam]

So power is changing in surges... and the MP gauge is showing it as well...(?)

Things that generate power can be...

1) exhaust pressure delivered to the turbo.  But when that fails, it doesn't usually come back...

2) airflow through the Turbo. When was the last time the Turbo saw an OH? Again, more of a one way issue.

3) oil being delivered to the bearings.  Unless oil level in the Turbo is changing....

4) pressure controller for the Turbo?  Good place to look for variations that come and go...

5) proper lubrication of all parts related to the pressure Controller?

while generating this list, I recalled a discussion regarding the use of mouse milk on certain pressure Controller parts.  Might this be the issue?

Good luck finding the issue.

PP ideas, not even a Turbo owner...

Best regard,

-a-

Edited January 22, 2017 by carusoam

[kortopates]

So you are saying its not an indication issue but an engine issue?

Do you have an engine analyzer installed that can also provide MAP, RPM and FF?

 

 

[231MJ]

Thanks guys.  I don't have the modern sophisticated engine analyzer but I do know the MP changes by 1-2", the RPM changes slightly but I have not watched FF during the oscillations so not sure what it's doing.  The pressure controller is a good place to start.  Let's see what the IA says.

[gsxrpilot]

I'm afraid to fly my 252 without a good engine monitor. In fact I ripped out the EDM 700 and replaced it with an EDM 900 just to have all the info on the screen at the same time. But then I'm pretty new to these turbo conti's.

[chrisk]

I would start by reading the following.  http://www.avweb.com/news/maint/182847-1.html I love the diagram.

I'd pull the cowling and start with a good visual inspection before i flew the plane again. I'd carefully look at the induction system and the exhaust system for leaks.  
The exhaust is by far the most important, as leaking hot exhaust gas under pressure is a very serious issue.  Pay particular attention to the clamps holding the turbo to the exhaust, there was a discussion on those not long ago.   Induction tubes are also very thin.  Chafing can put a hole in them quite quickly. 

The interesting thing is the 30 minute duration into the flight.  I'd assume the oil is up to max temperature near the top of the climb, and well before 30 minutes.   This makes me think it is probably not the pressure controller or waste gate actuator.  Edit, after completely reading the article, I'd bet more on the waste gate.  Some days I am glad I have a really simple 231.....  but most days I really wish I had the MB engine.

 

Please do let us know what you find.

 

[Aron Peterson]

I have the SB engine on my 252 and I would say to check the fuel flow to see if it coincides with the manifold pressure surge.



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[WilliamR]

I've seen this exact same thing on an MB engine.  Try some mouse milk (get the kind where no mice were injured during the milking, ha!) on the wastegate arm (upper left, and a little inboard when looking at the turbo from the right side).  My experience has been that what's generally happening is a little bootstrapping due the arm sticking a little.  Of course, a good visual of induction and exhaust is always a good idea.

William

 

 

[231MJ]

Chris, Aron, William:

Thanks much for the input.  Chris, the article from AVweb is excellent.  I got the cowl off last weekend for the up-coming annual.  I checked the induction and exhaust system and nothing obvious but my IA is really good at seeing things that I don't.  The issue logically seems to be between the pressure controller and the wastegate actuator so the mousemilk on the wastegate arm is going to happen.  

I'll keep you posted on actions and outcome.

 

August

[jlunseth]

16 hours ago, WilliamR said:

I've seen this exact same thing on an MB engine.  Try some mouse milk (get the kind where no mice were injured during the milking, ha!) on the wastegate arm (upper left, and a little inboard when looking at the turbo from the right side).  My experience has been that what's generally happening is a little bootstrapping due the arm sticking a little.  Of course, a good visual of induction and exhaust is always a good idea.

William

 

 

+1. I don't know if the mouse milk is the answer, but the wastegate is, or more precisely, the wastegate controller.  There are several things that could happen to your wastegate, but from the sounds of your symptoms that is where the problem lies.

[231MJ]

Just finished a long(er) annual and wanted to report what we found regarding the fluctuating manifold pressure.

First - thanks for all the input - this community is really great and much appreciated.  

In addition to the ideas from you guys, I found this article from RAM very helpful (http://www.ramaircraft.com/Customer-Service/Troubleshooting.htm).  I first went to the wastegate, which moved very easily but I doused it with mousemilk anyway.  Then I used air pressure to test the waste gate actuator (a cylinder pressure gauge worked nicely for this).  The wastegate started to close at 15 psi and was fully closed by 38 psi.  It operated very smoothly with changes in air pressure.  The problem was elsewhere.    

We (the IA and me) then did a careful inspection of the induction system and we found the potential source of the leak - a clamp on one of the hoses from the intercooler to the induction manifold was slightly askew, and I mean slightly,  but apparently enough to allow a leak.  I was skeptical that this was the actual source of the problem but I have flow three times now and no more manifold pressure fluctuation in the climb our at cruise.  I have only gone to 9,000 feet so I'm not entirely sure the problem is resolved but the initial results are positive.  

Lesson here - check the easy stuff first (although testing the wastegate actuator was fairly easy).  If the conventional wisdom says the most common issue is a leaking induction system - check that thoroughly (like everyone advised).  Don't assume it's the most expensive/complex component, like the pressure controller.  

 

 

[carusoam]

Great follow-up, AOC.

Nothing scarier than a loss of MP over tall mountains.  Getting the engine to restart without pressure from the Turbo may require less altitude than you have available....

PPP thoughts only, not a CFI...

Best regards,

-a-

[Guest]

11 hours ago, aochabauer said:

Just finished a long(er) annual and wanted to report what we found regarding the fluctuating manifold pressure.

First - thanks for all the input - this community is really great and much appreciated.  

In addition to the ideas from you guys, I found this article from RAM very helpful (http://www.ramaircraft.com/Customer-Service/Troubleshooting.htm).  I first went to the wastegate, which moved very easily but I doused it with mousemilk anyway.  Then I used air pressure to test the waste gate actuator (a cylinder pressure gauge worked nicely for this).  The wastegate started to close at 15 psi and was fully closed by 38 psi.  It operated very smoothly with changes in air pressure.  The problem was elsewhere.    

We (the IA and me) then did a careful inspection of the induction system and we found the potential source of the leak - a clamp on one of the hoses from the intercooler to the induction manifold was slightly askew, and I mean slightly,  but apparently enough to allow a leak.  I was skeptical that this was the actual source of the problem but I have flow three times now and no more manifold pressure fluctuation in the climb our at cruise.  I have only gone to 9,000 feet so I'm not entirely sure the problem is resolved but the initial results are positive.  

Lesson here - check the easy stuff first (although testing the wastegate actuator was fairly easy).  If the conventional wisdom says the most common issue is a leaking induction system - check that thoroughly (like everyone advised).  Don't assume it's the most expensive/complex component, like the pressure controller.  

 

 

The old continental training manuals suggest pressure checking the induction and exhaust systems every annual or 100 hours as well as flushing the waste gate controller.

Clarence