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how do I disable limp home mode in an 84-87 ECU?

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  • how do I disable limp home mode in an 84-87 ECU?

    I'm trying to figure out how to run a 0-5V MAF with an 86 NA ecu with an 86T rom chip. I found the 0-5V output from the on board op-amp on the little daughter board, and jumped a wire from the MAF pin to after the op-amp, to the runner where the maf voltage was 0-5V instead of 2-7V. After trying to get it to work without success (it was running crazy rich, and able to go past 2K rpm) I returned everything back to stock, and now it runs more rich out of boost, and way lean into boost.

    So... where can I disable the limp home mode? Can I even get this ECU to work with a 0-5V sensor? Nistune is taking way too long to get my hands on, and I don't want to spend $1500 on a stand alone if I don't have to.
    86 hardtop shell, 93 SC300 engine, 95 soarer bellhousing, 91 supra transmission, 95 Q45 differential hubs and driver's side axle, 1992 300ZX turbo driver side axle and calipers, 2004 350Z Rotors, 87 300ZX front end/hood, 1999 Viper radiator, 1992 Mustang throttle body. Lots of glue and tape to keep it all together.

  • #2
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    • #3
      Bernardd wrote: here is one way, i believe someone has mentioned this before as an option. craziness if you ask me:

      http://ecu2.forumwise.com/ecu2-post-10382.html#10382
      depending on cost/complexity that's not a bad thing as a mod goes, rivals the inline potentiometer

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      • #4
        wow... I did exactly what they did, but before I read their post. We built another opamp that increases voltage by 2, and are installing it tonight.

        The reason I wanted to do this is because the E-manage will cap the voltage from the MAF at 5, but the MAF keeps going to 7. Essentially, I have been tuning with a 0-3V MAF, as the last 2 volts are cut off by the e-manage. If this works OK, then the E-manage could be a much more user friendly option, and is more available than nistune. It is still a piggyback, and therefore limited... but I have had great results with it thus far. Dyno numbers coming soon.
        86 hardtop shell, 93 SC300 engine, 95 soarer bellhousing, 91 supra transmission, 95 Q45 differential hubs and driver's side axle, 1992 300ZX turbo driver side axle and calipers, 2004 350Z Rotors, 87 300ZX front end/hood, 1999 Viper radiator, 1992 Mustang throttle body. Lots of glue and tape to keep it all together.

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        • #5
          StreetFighter wrote: wow... I did exactly what they did, but before I read their post. We built another opamp that increases voltage by 2, and are installing it tonight.

          The reason I wanted to do this is because the E-manage will cap the voltage from the MAF at 5, but the MAF keeps going to 7. Essentially, I have been tuning with a 0-3V MAF, as the last 2 volts are cut off by the e-manage. If this works OK, then the E-manage could be a much more user friendly option, and is more available than nistune. It is still a piggyback, and therefore limited... but I have had great results with it thus far. Dyno numbers coming soon.
          more available than nistune? all it takes is an email

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          • #6
            Hi
            Nice to see progress form other side. Check my last post here
            http://www.z31performance.com/forum/vie ... highlight=

            it looks that I have similar running rich problem than you. At least, 2V offset seems to work, as I can past 2500rpm. But strange is that it running rich even without AFM connected....

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            • #7
              if the AFM is disconnected, the ECU will dump fuel.
              86 hardtop shell, 93 SC300 engine, 95 soarer bellhousing, 91 supra transmission, 95 Q45 differential hubs and driver's side axle, 1992 300ZX turbo driver side axle and calipers, 2004 350Z Rotors, 87 300ZX front end/hood, 1999 Viper radiator, 1992 Mustang throttle body. Lots of glue and tape to keep it all together.

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              • #8
                it is not possible to run engine in fail safe mode with disconnected AFM?

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                • #9
                  it is ... the ECU uses a default AFM input value which injects enough fuel good to about 2000rpm before it leans out too much

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                  • #10
                    okay i've got an update on this. managed to get it running with an R33 RB25 AFM, after changing the values in the ECU

                    but you should be able to remap to any of the later model (Z32, Q45 etc) AFMs now

                    here is a bit of a tutorial
                    http://home.aanet.com.au/nistune/afmupgrade.htm

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