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Hi everyone,

I seem to have a random issue with the waste gate servo on my 914 UL (TSN 200hrs).

At power on TCU lamps self test for 1-2 sec, than switch off.

Wastegate servo performs self test from fully open to fully closed position, but then seems to overturn into the closed position and gets stuck there. ( image 1 in the attachment shows servo in the stuck position).

Yellow TCU warning light starts flashing, as it should.

If I power off and power on again the servo stays stuck and yellow TCU light starts flashing right away.

To free the servo up again I opened it up very carefully and reassembled it.

After that it worked for some time until randomly it turned too far and got stuck again.

I think the servo turns way too far into the closed position sometimes, but I am not sure about the cause:

Is my wastegate cable too loose?

Or is this an issue with the wipers inside the servo?

I also checked the nominal resistances at the servo connectors according to Rotax Maintenance Manual Heavy  912/914, 78-20-00 ( see image 2 in the attachment):

Connectors: E-C: 5,00 kΩ > ok

Connectors: E-D: 5,02 kΩ > way too high, should be 0 to 70 Ω ! 

Connectors: C-D: 5,6 kΩ > ok

Connectors A-B: 10 Ω > ok

 

Did anybody experience this issue before maybe and know a solution?

Many thanks for your help everyone!

 

 

 

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10420_1_IMG_1012.jpg (You do not have access to download this file.)
  • Re: 914 wastegate servo issue

    by » 4 weeks ago


    Hello Tom,

    I really don’t know however this might be a mechanical issue rather than electrical. I wonder if the high resistance reading you found on pins E-D is because the servo had “over travelled”? Was it in the 0% position?

    The Line Maintenace manual 12-20-00 Page 65 describes the inspection and lubrication requirements for the waste gate. It makes reference to Heavy Maintenance Manual 78-00-00 for adjusting the waste gate but I have found that information to be in the Heavy Maintenance Manual 78-20-00 Pages 22-25. (It describes the installation and adjustment of the servo motor and waste gate control components.)

    It might be worth cleaning, lubricating and adjusting the mechanism before looking for electrical problems.

    Rotax Owner video here 

    https://www.rotax-owner.com/en/videos-topmenu/elearning-videos/280-wastegate171

    Cheers, Des.

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    39562_2_IMG_2401.png (You do not have access to download this file.)

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