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Thread: been chasing a gearbox issue....

  1. #1
    Join Date
    Sep 2005
    Location
    Garden of England
    Posts
    2,342

    Default been chasing a gearbox issue....

    for quite some time i've been getting an occasional gearbox 'glitch'.....

    every now and then, it decided to move the shift points of the gearbox up, and not be completely happy, til the car was switched off and restarted.... if it happened an off/restart cycle meant the gearbox continued as if nothing had happened! no 'down time' needed, instant restart cured it.. def hints at electrical, rather than mechanical/hydraulic...

    connecting the test point to get the blinky/flash dash indicators showed nothing.....

    as i had another spare gearbox ecu (actually got 2 spare!) I swapped that in, but it eventually showed the same issue! hmm not that then!

    i was going to ask on here or Prime, but as the usual advice is 'put in a manual' or 'it's not a proper NSX', i didn't bother!

    eventually i did it again, and this time i thought to check the diagnostics with the engine still running... sure enough we have a fault code! hurrah! 3 lovely flashes!

    this points to the gearbox ecu losing the throttle position signal (permanently or momentarily makes no difference, once it's lost, it defaults to lost until it's reset!)

    this tallies up with what i see at the fault condition, the computer moves up the shift points as it doesn't know what the throttle level is, and loses kick-down and torque converter lockup!

    so now i know it's the blue wire, i checked as per the manual, levels where expected,changing with the throttle position, disappearing when the throttle pot is disconnected so i know i have the right wire......

    connections checked and cycled, trying to replicate any loose connection, alas no

    on the way to goodwood we had to brake on a particularly rough surface at some traffic lights.. after that the gearbox was not happy... again 3 flashes in the OBD test condition.....

    moving away from the ecu, tracing the wiring loom, i find the connectors between the engine loom, and the 'floor' loom.... mounted on a weak mount and in fresh air behind the drivers seat.... hmmm that could be subject to vibration.... so the connectors oiled and cycled a few times, and then supported with some foam.....

    fingers crossed!

    IMG_20180715_115421 by jon sutherland, on Flickr
    aka Jonathan!!

    '92 charlotte green auto.... as a daily
    '37 Ford Y street rod......... something for the weekend!

    photobucket patch if you use chrome https://chrome.google.com/webstore/d...fegnfnflicjjgj

  2. #2
    Join Date
    Mar 2013
    Location
    Crawley
    Posts
    1,606

    Default

    Very impressive diagnosis and hopefully rectification there Jonathan, your problem solving is like rocket science compared to my recent battery problems.
    I hope you've cured it.

    What did you think of FOS this year???
    Pride.

    1992 My beloved Red/Black manual NA1.😎
    1992 Chevy Lumina apv Rockford Fosgate sound system demo van.🙉
    2003 Hartge Mini Cooper S (2 x UK & 1 x European sound quality finals winner) 🏆 

    "The NSX's greatest victory was to WIN the 1995 Le Mans 24hr GT2 Class"
    ..............and guess what, it was a RED one but of course.  

  3. #3
    Join Date
    Sep 2005
    Location
    Garden of England
    Posts
    2,342

    Default

    fingers crossed its sorted, it's the first time i've fiddled in that area, when various other investigations/swaps/changes had had no effect, so promising! just got to wait and see, the problem with intermittent faults!

    i'll start a FOS thread with some pix!!!
    aka Jonathan!!

    '92 charlotte green auto.... as a daily
    '37 Ford Y street rod......... something for the weekend!

    photobucket patch if you use chrome https://chrome.google.com/webstore/d...fegnfnflicjjgj

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