C340a MP lost at Alttitude – Waste Gate or WG Controller?

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  • #84169

    Need some help troubleshooting an issue and finding a good shop to use in the charlotte or surround area. This has been happening off and on for the past few months and it’s got to get fixed. I keep being told the problem should be solved and it never is.

    The scenario:
    I’m flying at FL190. MP is set to 31.5″ RPM 2300 per my RAM specs burning 20gl/side. Instantly the MP drops to 15″ on my left engine which my first concern (other than flying the plane of course) was the engine and turbo shock cooling. The MP then jumped up and down between 32″ and 15″ back and forth for about a minute before it finally stabilized down at 15″. You can imagine the ride conditions while the prop governor was trying to keep up with the massive changes in power on the left side. I began my decent since the pressurization system was freaking out due to the engine changes. The manifold climbed slowly back up as expected during the decent.

    Once on the ground at my destination, I had the cylinders checked for compression and all made it through just fine. Tough engine.

    What’s been done leading up to this point (before the flight):
    I’ve been seeing this issue creep up over the last few months. Each time having the systems checked by my mechanic. I’m told there is carbon building up in the waste gate controller and that the waste gate is sticking. The most recent work was this: they drained all the oil out of the engine, flushed the engine with fuel to try and clean out any carbon left over from some blowback in a few cylinders we had new rings put in months ago. They back flushed the waste gate controller so that it would seat correctly and they lubed the waste gate with mouse milk (this has now been done several times).

    My questions:
    1. Is the culprit in your opinion the waste gate or the waste gate controller or both?
    2. Is there another underlying problem that is causing the issue that we need to be looking for (or is the system just old and needs to be replaced)?
    3. Who in the charlotte, Greensboro, or Atlanta area do you recommend to have the plane taken to from now on?

    Thanks for your help with this issue!

    #98568

    What’s the fuel flow doing during all of this? How are the magnetos? Might be worth checking those as well.

    #98569

    Since you don’t have a mechanic that you are working with currently, I suggest calling Gary Main or one of his technicians at Main Turbo ( 1-888-847-8008 or mainturbo.com). They provide excellent support, including troubleshooting, as well as reasonably priced overhauls.

    Geoff

    #98571
    quote TDUPUIS:

    What’s the fuel flow doing during all of this? How are the magnetos? Might be worth checking those as well.

    Original fuel flow was right at 20/gal then as the power came back, I had to lean the mixture because as a result of the high altitude and low manifold the engine began to run rough due to the mixture being to rich. I don’t remember exactly what is was, but after leaning, it was close to half. About 12-14gal. The mags are all good. Thanks for the reply.

    #98572
    quote COCHRANE:

    Since you don’t have a mechanic that you are working with currently, I suggest calling Gary Main or one of his technicians at Main Turbo ( 1-888-847-8008 or mainturbo.com). They provide excellent support, including troubleshooting, as well as reasonably priced overhauls.

    Geoff

    Thanks Geoff. I’ll give them a call.

    #98573

    I don’t know how it works in the 340, but I had a similar issue in my T210. I was flying happily along and the MP dropped like there was no turbo at all.

    Long story short, it turned out to be the APC (absolute pressure controller – in the 210 this is what regulates the wastegate position). We replaced the APC and all was well.

    While it could be the turbo or wategate itself, the rapid changes doesn’t seem like a wastegate problem, but rather a turbo controller issue.

    There’s an easy way to test this which will force the wastegate closed (you cap one of the wategate oil control lines, but I don’t recall which one). Of course, this means you have to regulate power just with the throttle and it is VERY easy to overboost the engine. I suspect it’s a lot easier to manage this on a single than on a twin where you would have two very different throttle positions for takeoff.

    Another thought would be to swap the APCs between the two engines and see if the problem follows. Not sure if that’s practical to do in a 340 or not.

    Robert

    #98583

    I’d say it would be the APC or waste gate. As Robert days swap the APC to see if problem swaps side. It’s a bit of a pain but not too bad. First I’d pull the waste gate, which is a 30 min job and check with shop air that it is working smoothly. You need to keep it lubricated with mouse milk. I find at FL190 I need to run RPM at 2350 to 2400 BTW to keep turbo working well.

    Andrew

    #98591
    quote avann:

    I’d say it would be the APC or waste gate. As Robert days swap the APC to see if problem swaps side. It’s a bit of a pain but not too bad. First I’d pull the waste gate, which is a 30 min job and check with shop air that it is working smoothly. You need to keep it lubricated with mouse milk. I find at FL190 I need to run RPM at 2350 to 2400 BTW to keep turbo working well.

    Andrew

    I answered on the other thread if the carbon is in the engine oil system. If it is the wastegate, you can check by hooking up shop air like Andrew suggested. Just need a regulated air source and ideally a fixed leak (AN cap with a small hole in it) Wastegate response should be ~linear with pressure and no dead spots.

    However,if the MP in cruise is fluctuating from a stable point, and the MP is going down I think this is much more likely to be a turbo controller issue.

    are you getting extra oil on the belly from the turbo controller? One possible mode is the leak rate is well above spec and the controller is mechanically positioned for the right MP – but because of the oil leak the actual wastegate pressure is lower and hence more bypass, lower MP.

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