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On my 914 turbo
1st: the orange tcu light was blinking right after main key to on position (not run)
indicating sensor/wiring/servo motor problems???
2nd: checked servo motor operation ...moves from 8:00 to about 12:00 ...so "OK" then check all wiring connections ..."OK"
3rd: setup the TLR46 software that matches my TCU (741) .... went to monitor.... turned main key to on... everything reads normal except airbox temp... it reads "00c" should read about "16c" if I unplug the sensor the reading goes to "50c"
4th: checked the resistance of the sensor reads about 105.8 which should be equal to about 16c... so pretty sure the sensor is "OK" Engine has about 6 hours on it and was changed from 1 airframe to a newer airframe ran fine before the switch
5th: Disconnected main harness from TCU and sensor, checked continuity to ground from both pins at sensor plug.....none... wire "OK"?? checked continuity to ground at the temp sensor pins....none..."OK"
Any ideas ?? Thanks
Jay
  • Re: 914 Airbox temp sensor

    by » 6 years ago


    1: yes, the yellow lamp is for sensors, servo and wiring
    2: OK
    3: 50c is the default number for this sensor, if it fails it will default to 50c to protect the engine.
    4: good resistance check, OK
    5:Wire damage most likely issue:check continuity between sensor plug and wires #3 and #4. see pinout of TCU connector attached (viewed from wire side of connector!)
    TCUpinout.pdf (You do not have access to download this file.)

  • Re: 914 Airbox temp sensor

    by » 6 years ago


    Yea thanks for the input ....I was really hoping for a short or brake in the harness somewhere but I just got a test TCU in today and it fixed the problem.... Before I spend the $2600.00 on a new one I'm looking for what could be wrong with the "new" 5 hour old TCU that was in there. Not having any luck finding schematics .... but I kind of figured as much. Thanks for the come back Rob....was wondering if anyone was out there....;) Any more ideas are greatly appreciated especially if you know of someone who repairs the TCU units.
    Thanks
    Jay

  • Re: 914 Airbox temp sensor

    by » 6 years ago


    is it just a damaged #3 or #4 pin in the TCU? just straighten it?
    check the f/m pin on the wire side is not pushed out. you can pop the white cover off to inspect them.

  • Re: 914 Airbox temp sensor

    by » 6 years ago


    OK... Rob here's what I have done..... after finding out from the test loaner TCU worked I knew my TCU was the problem. So..... I tore it apart traced pin #3 & #4 back to a IC 7805 which is a 5v regulator that can be found at any electronics parts store......... well a good electronics store ;). Any way it is a 3 pin IC that can be soldered in. What I found out 1) the number on the IC can have letters in front and back of the IC like: TS7805 or L7805CV the letters tell what manufacturer made it but the IC is the same 5v regulator. 2) The TCU has a circuit on both top and bottom of the circuit board..... hard to unsolder (for me anyway) 3) Make sure both sides are soldered 4) there is also a rubber silicon covering some of the IC and Caps that needs to be cut off before you start your repair 5) the IC7805 cost me 0.90 cents plus $4.50 for a tube of silicon for vibration. Rob, thanks for your input, it's nice to have someone throwing ideas back. Thanks Jay

    Update!!
    Not out of the woods yet..... get back with you tomorrow....

  • Re: 914 Airbox temp sensor

    by » 6 years ago


    Well "tomorrow" turned into a bit longer.... After running my H3 with the 914, for about 2.5 hours, everything looks good, temps up and cooling down correctly, turbo working correctly and everything staying in the green (and no warning lights!!) ...... For the last few days I have been figuring out my ACES Cobra II balancer .... Looks like everything is tracked & balanced so....I'm feeling real good about the results so far .... Thanks Rob for all your input. Jay

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