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Thread: been chasing a gearbox issue....

  1. #1
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    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 red/yellow 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
    Last edited by britlude; 20-09-2018 at 10:31 PM.
    aka Jonathan!!

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

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  2. #2
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    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"
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  3. #3
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    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

  4. #4
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    So, it's still ongoing, it was ok for 2 weeks then returned, so another cycle of the connections and all was well for a few days, then the same again....

    So next step was to put a jumper wire between the TCS computer and the gearbox controller.... this worked briefly, but didnt cure it.... soo bypassing all the connectors, I linked the wire coming into the cabin and the link wire i'd added between the computers..... Hmm still occasionally going into fault mode....

    So... What is actually going on? I've tried a different controller and get the same error.... Back to first principles... Start at the top... Is it the throttle position sensor? So unplug it and drive off... Instantly I get engine management light, then TCS, while the gearbox is going into its fault state.... Right so the sensor error trips all 3 computers, but my normal fault is JUST the autobox controller... That narrows it down to just the connector to the computer and it's associated 3inches of wire (before the bypass link.... ) all the other in cabin connectors are bypassed and we know the signal is good at the TCS computer... Think we're getting close!!!!
    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

  5. #5
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    Quote Originally Posted by britlude View Post
    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.....
    The "rough surface" caught me here. It looks likes the intermittent error is pronounced by vibration. Maybe you'll find a way to monitor the voltage signal of the throttle position signal while driving.

  6. #6
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    right, to recap.... the gearbox has been having the occasional glitch for ages, and finally set about tracing it!

    here's the basic wiring diagram... engine, sensor, and 3 computers connected to the throttle pot sensor
    IMG_20181105_103303 by jon sutherland, on Flickr

    the first mod was to add a link between tcs and autobox controller....
    IMG_20181105_103426 by jon sutherland, on Flickr

    worked for about a week, but still played up, so take a feed upstream of the suspect connectors, eliminating them to the autobox computer...
    IMG_20181105_103500 by jon sutherland, on Flickr

    again worked for a while but then showed itself again...... so next step was to eliminate the engine loom, unsure whether the tcs and engine ecu would see the throttle signal momentary glitch, like the autobox did.... they didn't show error messages, but was that because they weren't required at the time so the computers ignored them??...

    so, i needed a throttle sensor connecter like this....
    IMG_20181017_161532 by jon sutherland, on Flickr
    Last edited by britlude; 09-11-2018 at 11:11 PM.
    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

  7. #7
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    fortunately the connector is used on many Honda vehicles,, and a motorbike one was sourced!!! and added to a cable...
    IMG_20181019_143738 by jon sutherland, on Flickr

    and this was wired into the loom, feeding in to my new wires, and tapping into the logic level voltage commoning block.....
    IMG_20181105_103545 by jon sutherland, on Flickr

    so now the entire throttle pot wiring was bypassed into the car and to the autobox computer...... all ok

    then it wasn't!!! so the only 'old' wiring to the autobox computer was literally 2 1/2 inches long!!! everything else had been eliminated.....

    just to be awkward i couldn't find any of the loom connector plugs, and couldn't find the supplier i'd used to get the abs loom connectors.... second hand pigtails were available in america but had the associated lead time.... but i did eventually find an ecu adaptor....
    s-l1600 by jon sutherland, on Flickr

    ok, i got more than i needed, but it did give me a chance to establish the connector retaining method!!! so another wire was added.....
    IMG_20181105_103609 by jon sutherland, on Flickr

    when i tested the suspect wiring connector in the plug it seemed 'looser' on the test pin than the other connections, so might be onto something

    now, touch wood, it's been behaving long enough to have eliminated the problem (sods law might kick in now i've posted this!) and i can start removing redundant links that i had added..... starting with reinstating the original engine loom.....

    fingers crossed!
    Last edited by britlude; 09-11-2018 at 11:15 PM.
    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

  8. #8

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    Thanks for leading us auto transmission owners through these complexities.

  9. #9
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    engine bay bypass wiring disconnected and original reinstated...... all ok so far, time will tell!!
    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

  10. #10

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    Fingers crossed. Jonathan.

    Full marks for tenacity!
    2001 3.2 Circuit Blue Coupe with pop-ups!

    "If you want to argue that The Best Car in the World is a supercar, go ahead. But there is only one that makes the grade. Only one that's built properly.
    Gordon Murray knows.
    Rowan Atkinson knows.
    It's the Honda NSX."
    (J. Clarkson)

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