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Thread: Best harness/ecm to use?

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    Best harness/ecm to use?

    Hey guys, this is my first post here. I joined up because I've committed to putting an LE5 2.4L Ecotec engine into my Mazda Miata and thought some insight from the guys who know the motor much better than I do would be helpful. The engine I purchased is from a 2007 HHR, and until it gets here later this week I'm not entirely sure what it is and isn't going to come with in terms of sensors, wire harness, manifolds, etc. I am assuming, however, that it will not include a wiring harness or ECM so I've been shopping around for those parts. I've seen the "stand-alone" harness/ecm package at CBM and other places, which looks very nice and sounds exactly like what I need, but at the $1k+ price tag it puts a significant hit into my budget so I'm trying to find used OEM stuff. Obviously I will need to have the ECM flashed to remove VATS, tell the ECM I'm using a manual transmission, load a performance tune, etc. but I'm wondering if there's certain years or vehicle types that will be more compatible/incompatible or that are better from a performance standpoint? I don't mind having to extend sections of the harness or clip out unused connectors if I have to for my specific use, but I certainly don't want to have to buy anything twice so any guidance would be much appreciated!

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    Depending on what you intend to do with the Ecotec-swapped Miata, you might be okay to use MicroSquirt.

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    Depending on what you intend to do with the Ecotec-swapped Miata, you might be okay to use MicroSquirt.
    Fallen2603 Quoted Post
    Microsquirt controls fuel only, so it would need to be used in conjunction with a stock ecm anyway. I'm currently running the miata engine on a megasquirt 2 module but the LE5, due to it's VVT, would need to be run on a MS3/MS3x in order to get control of everything. I am trying to stay away from a standalone at the moment, not only is the cost of hardware high, but after you factor in 500-1000 to have somebody else tune it, it gets quite expensive. I like the reliability of an OEM ecu and reliability is my whole purpose of doing this swap in the first place. My experience with megasquirt has been one obstacle after another, and it's a very finicky system. For example, my alternator went bad and I dropped to 11.7V, suddenly my coils no longer had enough power to fire, the car sputters out and dies. With a stock ECM, you could potentially keep being able to drive it all the way down to a theoretical 9V, which should give you plenty of time to pull over somewhere safe, not die in the middle of a busy road as what happened to me....

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    MicroSquirt CAN control ignition, just not in a COP format. You'd have to do two double coils in waste-spark mode.

    If you want to keep the VVT, yes, you'll have to use the OEM ECU, MS3/MS3x, or AEM EMS-4.

    It sounds like you've already made you decision.

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    MicroSquirt CAN control ignition, just not in a COP format. You'd have to do two double coils in waste-spark mode.

    If you want to keep the VVT, yes, you'll have to use the OEM ECU, MS3/MS3x, or AEM EMS-4.

    It sounds like you've already made you decision.
    Fallen2603 Quoted Post
    Yes I have, my question pertains to what ECU/wire harness is best to get. I.E. is one from a 2006 cobalt SS any better than one from a 2010 Malibu? If I use an automatic ECU/Harness on a manual transmission car is it going to cause check engine lights? Can the harness and ECU be mixmatched from different cars like would a harness from a 2006 Pontiac G6 and an ECM from a 2008 Saturn Vue be compatible? Were there sensor changes between years that would necessitate me going with a year of harness the same year as my engine? These are the types of things I'm trying to figure out, I greatly appreciate any help!

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    The most user friendly harness would be from 07-08 solstice or any of the E67 ecu cars. Rework what you have and save at least half of a new system. Questions? Pm me. Steve

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