josok-e(at)ukolo.fi
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 Posted: Sat Feb 09, 2008 11:19 am Post subject: 914 turbo questions |
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Careful, long and complicated story. Dive in it on your own risk.
The general understanding, or at least my limited knowledge, seems to be that the turbo only starts charging over 100%. However, i had a problem earlier in the week. Outside temperature was -15 C and the plane had been washed in the warm workshop. Started the engine after about 10 minutes outside, and waited for the oil to be 50 C. All indications were normal. Then i put in more power, and noticed that the second half of the throttle control did not do anything. The engine would not run faster then 35400-3600 rpm. Stopped the engine and took the cowlings of to check that the throttle levers on the carbs were operational. They were.
Back in the workshop i checked about everything i could think of. Found nothing. Noticed that the TCU opens the waste until half throttle, and closes it again when moving the lever to full throttle. This on a non running engine. Had a look at the log in the TCU and noticed that the waste gate had been doing the same with the engine running. Yesterday took the plane out again, and had another run. OAT -5C. Now full revs could be reached, problem gone.
The TCU log now showed up to full waste gate opening, and opening already started at 3600 rpm. Interesting was, that closing the throttle a bit from high revs, opens the waste-gate further. Have a look at the attached log. I assume now that the intake side of the turbo had been frozen, so that the turbo would not run during the first attempts.
Just a condensed, frozen droplet on the impeller is probably enough for that. During the heat up run, air at very low temperatures could keep the ice there, even if the other side of the turbo is hot.
I also assume that if the pressure in the air box not rises if the waste gate opens, the TCU starts closing it again. Too much assumptions probably 
Comments please!
Regards,
Jos Okhuijsen
Visit - www.EuropaOwners.org
Attachments:
http://www.europaowners.org//zfiles/02081620_135.txt
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