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Megasquirt woes. Giving up and selling for speeduino.

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    Megasquirt woes. Giving up and selling for speeduino.

    Giving up on my megasquirt 2 v3 setup, I tried to wire using the diagram here, https://www.e30zone.net/e30wiki/images/7/75/2dhs0fn.png

    I found pin 1 on the motronic connector which is farthest away from the cable.

    Also using the universal wiring diagram for the megsaquirt. Followed the guide here https://www.diyautotune.com/support/...-your-bmw-e30/

    And this guide https://www.e30zone.net/e30wiki/inde...rting_Your_M20


    Any ground I run to the body from the db37 just creates a short and sparks. The main relay turns on when I plug the db37 connector in.

    Tried running 12v power to pin 28 and pin 9 ground on db37 connector - no connection on the RS232 port can be made in Tuner Studio. No lights on the megasquirt.

    Not sure if the MS is bad. I bought it second hand from what I was told came out of a running e36

    Not sure whats going on, and I don't want to have to buy a megastim just to find out it's not working properly.


    I'm pretty good with electronics and schematics. Spent the whole day wiring and making sure everything was right, so definitely bummed it didn't work out.


    Not to mention, rats ate some of my harness in the dash. I figured I would at least get power to the MS, connect to it with PC and at least get a connection from one of the sensors.


    I listed it for sale on ebay right now and just bought a speeduino 0.3.7 which has all the outputs labeled. which should make things a lot easier.

    Just can't put my finger on why the multiple grounds on Megasquirt DB37 at 19,18,17 would spark/short out when touching chassis ground?


    #2
    If rats had at your wiring you'd better triple check everything or you'll just smoke the speeduino too. The stock ECU triggers the main relay by grounding harness pin 36 when it gets +12V on pin 27. If the main relay turns on whenever the DB37 is plugged in then whatever you routed harness pin 36 to on the MS/adapter is grounded. The trigger circuit is something I never bothered with, I join harness pins 27 and 36 in my adapter, cut the power wire to pin 86 on the main relay, and ground it. It's the easiest method, and when the key is turned on the relay turns on. If a stock ECU is ever to be used in the car again the mod to the relay connector must be reversed, luckily it's exceedingly easy.

    Originally posted by Davidb785 View Post
    Just can't put my finger on why the multiple grounds on Megasquirt DB37 at 19,18,17 would spark/short out when touching chassis ground?
    Because one of your grounds was somehow fed +12V and they all share the same ground plane. Did you try probing the pins on your harness and adapter with a voltmeter and verify +12V is only where it should be and there is ground continuity where it should be? Disregard colors and probe with a multimeter. The Germans are obtuse and use nonstandard ground and positive wire colors when it suits them, it's easy to mess up and not ground what should be grounded or put +12V where it shouldn't be. Especially when installing an engine harness where there are branches that are for ground and power right next to each other.

    Originally posted by Davidb785 View Post
    Tried running 12v power to pin 28 and pin 9 ground on db37 connector - no connection on the RS232 port can be made in Tuner Studio. No lights on the megasquirt.
    The above incident where your DB37 sparked cooked it. Depending on what was grounded but shouldn't be or powered but shouldn't be it is either a smoked regulation circuit component or more likely there's enough burned up that repairing it is best left to an expert.

    It's my opinion that someone's first megasquirt should either be a fresh kit build for a car with known configuration or one for that specific car that was expert built. Modifying something that was already configured for a different car by someone of dubious capability invites trouble if you aren't familiar with what jumpers and mods should and should not be present. E36 and E30 configurations are fairly close in my experience, but I don't know what yours looked like or what your level of familiarity with it is.
    Last edited by varg; 08-09-2020, 11:24 AM.

    IG @turbovarg
    '91 318is, M20B25 turbo
    [CoTM: 4-18]
    '94 525iT slicktop

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      #3
      After reading the resources you posted and still being confused, I made this thread to help anyone else looking to go standalone. Not to toot my own horn, but *toot*

      https://www.r3vlimited.com/board/for...ild-and-wiring

      I know you're abandoning MegaSquirt, so the build info isn't useful. The rest of the setup and wiring should be pretty helpful though.
      Last edited by McGyver; 08-18-2020, 08:38 AM.
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