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Thread: Hacking the Autobox ECU

  1. #21
    Louis's Avatar

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    Remember "Wave Spring", issues when you are tweeking!

    Might be better testing ECU mods on a car that has had the wave spring replaced!


    https://www.clubvr4.com/forum/showth...ht=wave+spring
    Updating Soon!! 1998 Legnum VR4, fully serviced every 4500 miles. Fully Amsoil'd. Falken 453's, EVO 8 FQ320 rear diff.

  2. #22
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  3. #23
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    Quote Originally Posted by Confused View Post
    This is great, it was so annoying when you crawl to near stop an box drop to 1st, how to flash box with that mod?
    His FL Legnum VR4 running 238.8 ATW HP and 500Nm @1.05 bar on LPG
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  4. #24
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    i can do it you need mmcFlash dongle.

    Bye for Now!

  5. #25
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    It's still very early days, I'm sure there's more tweaking needed to make this change better then the drop into 1st - this is a couple of guys theorising and applying some basic tweaks to some tables we think define something, compared to Mitsubishi's engineers working dedicated on this!

    But, currently, myself, @Davezj and @foxdie have the equipment and current knowledge to apply these changes - but we are still working on it, and still have lots of testing until we've got something we'll be confident in applying to other people's cars.

    The key thing is that we've managed to do something we don't think anyone else has managed yet, which is to change the 3-1 downshift behaviour, which proves it is possible, but we might try find out good reasons why it was done this way, and why changing it might not be a good idea.

  6. #26
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    Yeah there's a LOT of work left to be done - I was up until 1am last night reverse engineering the ROM with a hex editor and found at least 20 undocumented tables in the PFL TCU ROM that need analysing and publishing.

    Today I've been fiddling with the shift points, trying to get the car to get up into a higher gear earlier, got mine shifting up to 4th gear around 20 MPH and 5th gear around 30 MPH.. (my speedo reads 10% high..)

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  7. #27
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    Some great work going on here guys. Well done.
    '97 Manual Legnum in silver with some subtle mods

    My first VR4 - '97 Legnum Dark Green & mean ...it was love at first sight - now sold

  8. #28

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    Quote Originally Posted by Confused View Post
    The key thing is that we've managed to do something we don't think anyone else has managed yet, which is to change the 3-1 downshift behaviour, which proves it is possible, but we might try find out good reasons why it was done this way, and why changing it might not be a good idea.
    Really cool that you managed to make a tweak like that. As for the stock downshifts when decelerating - I am guessing it is done this way because the autobox ECU is minimising wear by not picking gears unnecesarily. Easy to imagine that this simple strategy saves hundreds of gear shifts during a day of city driving. Another possible reason - read somewhere that it is unwise to engine brake using an autobox (risk of overheating something due to the box reverse-driving the engine). The default strategy seems to indeed avoid engine braking by staying at a high gear until car comes to a stop.
    The more you know, the faster you can go. And I still don't know enough.

  9. #29
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    The VR4 drops a gear going down hills if the car is gaining speed with no throttle input. So engine braking can't be so bad?

  10. #30

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    Something i noticed is that when moving very slow, in third (heavy traffic on M3 northbound) the gearbox seems to detect a need for engine braking in the same way as the more common 5-4 shift.

    Rolling at about 15 mph, slight downhill, slowly gaining speed. just about to reach for brakes and the revs jumped from ~800 to 1600, speed dropped fast, then revs dropped suddenly from about 1200 - 800 after speed was down to say 10 mph. Im guessing it enabled TC lockup? that or it was in 4th and i was mistaken (seems unlikely, had been 0 throttle from a standstill for a while). Perhaps this is a part of the 3-1 strategy and when it detects heavy braking (or downhill) it will make much more of 3rd gear braking than normally seen in an auto?

  11. #31

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    Quote Originally Posted by Nick Mann View Post
    The VR4 drops a gear going down hills if the car is gaining speed with no throttle input. So engine braking can't be so bad?
    Thanks. Never encountered that, interesting... Can't find the source of where I read that bit about engine braking.

    Come to think of it - the autobox is a fluid and a mechanical coupling. So as long as the oil pump is running and clutch packs inside gearbox are fully engaged, there should be no ill effects.

    I still stand by my comment about avoiding unnecessary gear shifts being the default strategy. This is also very annoying on trackdays.

  12. #32
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    When traveling very slowly in 3rd gear.
    If you get on the throttle at all the gear box may well try to change down to 1st before moving off. But sometimes the gearbox will try and change down to 1st and then about the change and go back to 3rd.

    Sent from my MI 5s using Tapatalk

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