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Thread: Are the OBD1 ECMs the same?

  1. #1
    Carb and Points! Pappy's Avatar
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    Are the OBD1 ECMs the same?

    Hey guys...I am completely new to this game so if this is a stupid question....bare with me. I want to start learning to burn my own proms and have invested in the equipment and software, but thought I would put in a little safe guard in case something was to go wrong. What I have done is acquired a couple ecms from a local yard here that I have a bit of a service related relationship with. They are ECMs out of chevy trucks like mine but they have different service numbers on them. Mine is a 1227747 and the others are not but they use the same prom. I have installed a socket adapter onto one of the other ecms and kept mine back for just in case. Problem is now that I haven't had any luck with getting my laptop to talk with my ecm I can't get the truck to take the stock ecm and prom. The SES light either comes on constantly, of flashes very rapidly depending whether or not I have my aldl cable hooked up. Now, from what I can tell so far by reading here and there this is a sign that the ecm is in "fault mode" or "limp mode". If that is the case what do I have to do to get my stock ecm loaded back into my truck? Is there a procedure to take the ECM out of fault mode or should it correct itself once the factory prom is back in place. I appologize if this has been discussed before...I have read and read until my head hurts and I have so many things coming together in my head I am lost. Right now all I want to do is get my truck back to running again, then I can start from scratch and get back to learning the prom burning and tuning one step at a time from the beginning. At this point I am ready to pull the heads...put a carb set of heads on and go with a carb and intake.

  2. #2
    Super Moderator Six_Shooter's Avatar
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    For starters, in your case the only ECM that will benefit you IS a 1227747. You can not swap PROMs between a '7747 and another ECM (such as a '299), the bin file (software/firmware) is different between those ECMs and will not work in the opposite.

    Yes, once you have the correct PROM loaded, or rather bin file loaded to either an EPROM or an emulator (it sound like you only have EPROMS), the ECM will take itself out of LHM.

    Alternatively, you can use a '299 and the appropriate bin file (programmed to an EPROM), in place of a '7747, they are directly pin compatible and no changes to the wiring are needed.

    There are other ECMs, used in other applications where there is a certain level of swappability of EPROMs, but the C3 series (what you have) is not one of them.
    The man who says something is impossible, is usually interrupted by the man doing it.

  3. #3
    Fuel Injected!
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    If the other ECMs are not the same number as the 1227747, then chances are the pinouts on the other ecm's are different. I.E. you are using an ecm with pins A1-A5 wired to the ESC and the other ecm's pins A1-A5 pins are for the knock sensor and TPS. (that is just an example.)

    Check the following sub forum for the correct pin out for the respective ECM. Each number ECM has it's own thread with ALL associated info.

    http://www.gearhead-efi.com/Fuel-Inj...ms-Tuner-Info!

  4. #4
    Carb and Points! Pappy's Avatar
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    OK....thanks guys....I will get another 1227747 ECM and move my socket adapter over to it and try to start from scratch. I thought the ECMs were the same and the only difference was the PROM. I hope that is all it is. BTW....is there anything I need to do to clear the limp mode or should the stock ecm and stock prom with the original configuration bring the truck back to where it was before I started this mess?

  5. #5
    Super Moderator Six_Shooter's Avatar
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    As I said, the ECM will work fine once it has the proper EPROM in the proper ECM. Nothing special to do.

    Some people will suggest disconnecting power for a few seconds to clear the code 51, but it's not totally necessary in my experience, and besides that you will be disconnecting the ECM to swap them anyway, so it's really a moot point.
    The man who says something is impossible, is usually interrupted by the man doing it.

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