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Topic-icon Turbo induced engine surging

  • David Crass
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6 months 2 weeks ago #2114

It's taken a while, my A&P has been really busy, but the problem appears to be a leaking pressure relief valve. I fabricated a plate to blank it off and we did a ground run this afternoon, performed well! I discovered the leak on a second induction system inspection, I just missed it the first time around. The poppet is leaking badly on the back side, you can actually feel a breeze. We cleaned up the mating surfaces and checked it again and the leak was worse so I'll be sending it in for overhaul or exchange. I did soak the turbo center section with mouse milk over the weekend, but it spun freely before and after soaking. I pulled the propeller governor and took it into the prop shop, it checked out fine on the bench but the tech put me in touch with an A&P that's working with the same engine (new, 10 hours on the engine) in a turbo Saratoga that was surging as well. They discovered a leaking connection in the lines that provide pressure to the mags. The common denominator then would be any significant leaks in the induction system cause problems with the slope controller. I'll do another ground run after the overhauled pressure relief valve is installed and will give an update. Thanks to everyone that contributed to trouble shooting the problem!

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6 months 3 weeks ago #2110

I'm not familiar with the system you have on this aircraft but I flew a Cessna 340A for twenty years and maintained it as well. It appears you have done most of the things I would check concerning this problem but I might make a few suggestions. Does this installation have an alternate air source? If so you might check the installation and the sealing areas that prevent hot air from inside the engine cowling from getting into the normal intake. You stated there was a drop in performance after the engine warmed up.
One long shot that happened to me twenty years ago was a failure at the exhaust wye where the two exhaust pipes converge and are channeled to the turbo. there is a piece of metal that is welded inside to prevent the exhaust from creating turbulence when it converges. Mine broke loose and caused a restriction that pretty much reduced the flow that knocked the engine power down to that of a naturally aspirated version. Yours may not be that bad yet but just worth checking.
Good luck and keep us posted.

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6 months 3 weeks ago #2109

Hi David;
How about a status update?? Are all systems go??

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6 months 3 weeks ago #2106

David,
I do not know if there are restrictions in the oil lines to the turbo and wastegate.
There is a requirement to put a restrictor at the engine in the oil pressure line to slow the loss of engine oil if that line fails.
I suppose it makes sense to have on in all the engine oil lines but I believe that since the oil lines from the engine to the controller and from the controller to the wastegate are designed to provide sufficient flow to cool the turbine center bearing, so my guess is that there isn't one in those lines.
I just talked with Main Turbo and was assured that there are no restrictions in the oil lines of the turbo system. There is a check valve above the turbo that is designed to prevent oil from puddling in the center section (then leaking out past the seals into the compressor and turbine wheels) when the engine is off.

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6 months 3 weeks ago #2105

David,
Sounds like a good plan.
Please let me know how things turn out.
S

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  • David Crass
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6 months 3 weeks ago #2104

Steve,
My A&P/IA wanted me to check with you and ask if either of the oil lines on controller are supposed to be orifice fittings. Lycoming tech mentioned it to him and it's mentioned in the trouble shooting guide but the Lycoming tech couldn't confirm or give any guidance.
Thanks!
David

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