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Cant figure it out: Voltage drop when trying to start on AEM EMS (SR20)

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  • Cant figure it out: Voltage drop when trying to start on AEM EMS (SR20)

    My new motor is having some electrical issues. S13 Redtop with AEM EMS (MAP), when running the starter, voltage drops to 9-10V area from about 13-14V when starter is not engaged. I tested the starter out of the car at a few auto parts stores (on their starter test benches), and I get about 14V @ 75amps. All grounds looks to be good, and tested all the grounds on the ECU itself. Hoping someone has ran into this before, and has some insight. Before new setup, car started on a flashed factory ECU, but did take a little work to get it to start. The AEM ECU wont start the car at 9-10V.

    www.2LiterTurbo.com (Personal Site)
    96 240SX SE: Track Car | 90 Skyline GTR: Bucket List Car | 07 Legacy Spec B: The DD

  • #2
    We tried about 3 different batteries (one being brand new). The grounds that I can think of is the battery ground to the engine (with chassis in the middle), the small ones on the intake manifold, the one on the back of the cylinder head to firewall, and the one from the starter solenoid to the chassis. Am I forgetting any? All grounds in the ecu tested good as well.

    www.2LiterTurbo.com (Personal Site)
    96 240SX SE: Track Car | 90 Skyline GTR: Bucket List Car | 07 Legacy Spec B: The DD

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    • #3
      Do you see voltage from your ground location to your battery neg terminal? That would indicate a wiring problem.
      '18 Chevrolet Volt - Electric fun hatch for DD duty!


      DefSport Koni Sleeve and Spring Perch Buy!!!
      http://www.nissanroadracing.com/showthread.php?t=5902

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      • #4
        I'll have to check. It's at a shop (where it's supposed to get a tune), so it's kind of a pain to work on, especially because they don't like me working on it while it is there (which i find absurd, but whatever). I'd rather figure it out, than pay $80/hr to have someone else figure it out. I'm cheaper, lol.

        www.2LiterTurbo.com (Personal Site)
        96 240SX SE: Track Car | 90 Skyline GTR: Bucket List Car | 07 Legacy Spec B: The DD

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        • #5
          There's your answer- they're not making $80 an hour when you're tinkering with the car. Christ mechanics charge a lot.
          ~1992 240SX, SR20/Koni track day car
          ~2016 M3, daily driver

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          • #6
            Yeah, I know that is always an underlying reason, lol

            www.2LiterTurbo.com (Personal Site)
            96 240SX SE: Track Car | 90 Skyline GTR: Bucket List Car | 07 Legacy Spec B: The DD

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            • #7
              Has the the car started and ran on the AEM before? How many grounds do you have? Should have a ground for head, block, intake manifold, and tranny.

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              • #8
                It hasn't, and all the grounds are there.

                www.2LiterTurbo.com (Personal Site)
                96 240SX SE: Track Car | 90 Skyline GTR: Bucket List Car | 07 Legacy Spec B: The DD

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                • #9
                  If possible try and start the car with the old ecu, and check the calibrations in the ecu like cam sync and stuff.

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                  • #10
                    Oh and when you turn the key on wait like 5-10 seconds to crank aem is gay like that, some times if you crank to soon the car will idle at like 2000 rpm.

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                    • #11
                      The harness is all wired up for the AEM now with the map sensor/air intake sensor, etc. The old ECU is a ROM tuned z32 MAF setup. So would trying the old ecu mess stuff up. I hate not being an ECU guy, I sound like an idiot. Ha ha.

                      www.2LiterTurbo.com (Personal Site)
                      96 240SX SE: Track Car | 90 Skyline GTR: Bucket List Car | 07 Legacy Spec B: The DD

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                      • #12
                        You would have to convert every thing back. If you are trying to learn to tune yourself I would go to aem forums and search around there, I know nissans are a bitch with cam syncing. Or try finding a local tuner.

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                        • #13
                          It's at the local aem tuner, lol. Because I don't crap about ecu tuning.

                          www.2LiterTurbo.com (Personal Site)
                          96 240SX SE: Track Car | 90 Skyline GTR: Bucket List Car | 07 Legacy Spec B: The DD

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                          • #14
                            OK, went over to a buddy's house and tested the starter on his SR car (tested his starter as well), and there was only about a .5V drop (normal) max between the three different tests I did on both starters (ground, power, and solenoid). So it's not the starter at all. I get the AEM trigger wheel on Monday, so after I get that installed, I'll see if we can get it started. I'm still out of ideas.

                            www.2LiterTurbo.com (Personal Site)
                            96 240SX SE: Track Car | 90 Skyline GTR: Bucket List Car | 07 Legacy Spec B: The DD

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                            • #15
                              If the aem trigger wheel isn't installed it won't start, that was a big problem they had.

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