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Thread: Using small 12v battery to prevent re-learn of the ECU?

  1. #1

    Default Using small 12v battery to prevent re-learn of the ECU?

    I have noticed on other forums that when doing mods on the MPS's that if the battery is disconnected the computer has to re learn the fuel trims etc.. when it is re installed.This results in a reduction of power etc for a few days/K's.

    What i want to know is that if i hook up a smaller 12v rechargeable battery before disconnecting will this prevent it? Similar to when you use a 9v battery to prvent loosing memory power to the stereo...(what we used to do at a dealer workshop i used to work at)

    I dont really wanna wait a few days after doin a mod before i can see/feel any differences.

    Jason

  2. #2

    Default

    But isn’t it a good thing to reset your computer after each mod?? I thought it would be an advantage.

    It can be done. You’ll need to somehow splice a secondary 12v battery source into the + of the wire into your computer.

    After that, then you can disconnect feed from the car’s battery without dropping voltage to your computer. You may need to have a look at your car’s wiring diagram because I assume it will be similar to a car radio with one constant power and one from the ignition. The – will go to chassis.

    It is really that noticeable difference before and after the relearning by the computer in a MPS??

  3. #3
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    Default

    If you want to do it the quick and dirty way, all you'll need is a resistor, diode and a reasonably large capacitor.

  4. Default

    Dont make a mistake when splicing in the 2nd battery. If you do, say bye bye to your ECU....

    In anycase, you should have enough power to fuel the ECU for around 2 min after disconnecting the battery (with ignition off). Thats why you have to hold your foot on the brake after the disconnection to totally drain the system....

  5. #5

    Default

    Quote Originally Posted by Wardski View Post
    Dont make a mistake when splicing in the 2nd battery. If you do, say bye bye to your ECU....

    In anycase, you should have enough power to fuel the ECU for around 2 min after disconnecting the battery (with ignition off). Thats why you have to hold your foot on the brake after the disconnection to totally drain the system....
    hum.....that gives you 2 mins to install the modification.......Maybe if we have access to a F1 racing team, that would be awesome. “New gearbox please”,"yep no worries, give us 5 mins".

    ECUs are delicate things, I wouldn't risk it just for couple days drive. Anyway, it'll give you more of an excuse to fang your car!!!!!

  6. #6
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    The better way to do it is to go for a drive around your 'burb, pull over, turn the car off, wait a moment, then turn the car on and drive again. Just do this a couple of times and you should be good.

  7. #7
    Nevermind Guest

    Default

    People usually say the car feels faster and more aggressive after they reset their ECU. Either way, in a couple days its back to normal anyway, I don't see what the big deal is?

  8. #8
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    Quote Originally Posted by Nevermind View Post
    People usually say the car feels faster and more aggressive after they reset their ECU. Either way, in a couple days its back to normal anyway, I don't see what the big deal is?
    Pretty much.

  9. #9

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    The reason i wanted to do it was that i am currently upgrading the inlet and FMIC, i wanted to dyno stock, with just Inlet, with just cooler & with both all on the same day. Wanted to do a similar thing at the track too. otherwise i have no issue with waiting.

    By the sounds of things tho it benefits the car to reset and re learn.... Also safer for it aswell, am i right?

  10. #10
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