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NA6 Miata will not show codes in diagnostic mode but CEL lights up when running and runs like crap

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  • NA6 Miata will not show codes in diagnostic mode but CEL lights up when running and runs like crap

    I've got a problem I'm hoping you guys can help sort out. I picked up a 1992 Miata as a project a few weeks back and brought it back to life ( it had a bad transmission and diff).

    I've been daily driving the car for 2 weeks with no issues. Today, I went to run an errand and the car broke down on me. It ran perfect up until it reached operating temperature, and then had no power at all. The car would idle fine, but pressing the gas to the floor resulted in a check engine light and the RPMs bouncing between 500-2000 rpm, but the car would develop 0 power. It quit moving forward on me as I was driving up the Ashford-Dunwoody exit ramp off of I285. To get out of a travel lane, I had to floor the car (resulting in a max RPM of 1750 and bouncing around) and slip the clutch a ton to get the car to inch over to the shoulder. When I say no power at all, I mean it. It took about 30 seconds of the pedal to the floor and partially engaging and disengaging the clutch to get it to move 6 feet off the road. Any attempt to let the clutch fully engage would instantly kill the engine. If it died, I could restart it and it would idle fine, but any level of gas and it ran like $hit.

    After getting AAA to tow it back to my house, I attempted to pull the engine codes by connecting the TEN and GND pins in the diagnostic connector. When I turn the key to ON (without starting the car), the check engine light stays solid and never goes off to flash any codes. I've tried 2 different paper clips and a segment of scrap wire and the result is the same. I pulled the wire off, brought the car back up to operating temp and confirmed it still runs like crap. When running, any time I hit the gas, it runs like crap and the CEL lights up, when I let off the gas and let it return to idle, the CEL goes off. I have had it running, hit the gas multiple times to get the CEL to light up, then immediately shut the car off, connected the TEN and GND pins and turned the key back to ON and all that happens is the CEL stays lit solid. I've sat for over a minute watching it with the key on and nothing happens.

    Has anyone here ever been unable to get a Miata into diagnostics mode? I've had several other NA6 Miatas over the years and have successfully used diagnostic mode before. Any help/advice is appreciated.

    I did notice 2 things. Once the car cools down again, it runs better until it heats back up. The other is it smells really rich when it is running like crap... anyone had similar symptoms and advice on where to start?

    Thanks in advance for your help!
    2004 MSM - FM LE Package, VMAXX Coilovers, 6ULs, Boss Frog Double Hoop
    2014 Exomotive Exocet - NB2 VVT drivetrain, Xida Coilovers, Enthuza Exhaust

  • #2
    Sounds like a coil pack went bad.

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    • #3
      Off topic: dude welcome back! What's up with the Exocet?!? You were everywhere for a while...but I haven't seen you or the car in a long time?
      sigpic

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      • #4
        The CEL not responding makes me think your ECU shat the bed. Other than that, thermister sensor (the one on the back of the head with the green clip) or failing coils.

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        • #5
          AFM may have pooped too. Came get a box of stuff to try if you want to parts swap.
          David Luney - Suwanee GA
          [email protected]
          04 RX-8, 10 Black MS3, 08 Red MS3, 06 550i, 05 325i 92 Spec Miata and a parts car or two.

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          • #6
            Originally posted by kung fu jesus View Post
            The CEL not responding makes me think your ECU shat the bed. Other than that, thermister sensor (the one on the back of the head with the green clip) or failing coils.
            I'm leaning toward the ECU myself... I've been playing with the car for the past hour or so and found that the fan is not coming on at all. Checked the thermoswitch on the thermostat housing and it is definitely shot as the pin coming out of it is loose and the plastic sealant is cracked (the plastic surround literally broke off when I disconnected the harness).

            IMG_3671.JPG

            I was reading on other forums that jumping the GDN and TEN pins should turn the fans on when you press the accelerator, tried that but no go. When I turn on the AC both fans work as they should.

            Also, the ECU is behind the passenger seat, right? When I got the car, it had an improperly installed top (no tension cables and a cracked rain rail) and the passenger side foot well had some water in it. I've since put on a new rain rail, tension cables, reattached the passenger side drain, etc. and the car is water tight again, but I'm wondering if the ECU was damaged when water was getting in.
            2004 MSM - FM LE Package, VMAXX Coilovers, 6ULs, Boss Frog Double Hoop
            2014 Exomotive Exocet - NB2 VVT drivetrain, Xida Coilovers, Enthuza Exhaust

            Comment


            • #7
              Originally posted by nickt93 View Post
              Off topic: dude welcome back! What's up with the Exocet?!? You were everywhere for a while...but I haven't seen you or the car in a long time?
              Thanks Nick, the Exocet is still around, it's just sitting idle in the garage currently. Having a second child and switching jobs have killed any track time opportunities for me the past year or so :(

              Good news is I'm signed up for Jzilla at Road Atlanta, so I'm getting back into things!
              2004 MSM - FM LE Package, VMAXX Coilovers, 6ULs, Boss Frog Double Hoop
              2014 Exomotive Exocet - NB2 VVT drivetrain, Xida Coilovers, Enthuza Exhaust

              Comment


              • #8
                Originally posted by miatastuff View Post
                AFM may have pooped too. Came get a box of stuff to try if you want to parts swap.

                I think I'll take you up on the offer to grab some parts to swap... without the CEL to give me a starting point, that's probably the best way. I'll send you an email to check your availability.

                Thanks!
                2004 MSM - FM LE Package, VMAXX Coilovers, 6ULs, Boss Frog Double Hoop
                2014 Exomotive Exocet - NB2 VVT drivetrain, Xida Coilovers, Enthuza Exhaust

                Comment


                • #9
                  Originally posted by iscariot View Post
                  Sounds like a coil pack went bad.

                  Could be, but would it run absolutely perfect until warm if a coil was bad? I'm going to try swapping parts one at a time (including the coil) until I find the culprit...
                  2004 MSM - FM LE Package, VMAXX Coilovers, 6ULs, Boss Frog Double Hoop
                  2014 Exomotive Exocet - NB2 VVT drivetrain, Xida Coilovers, Enthuza Exhaust

                  Comment


                  • #10
                    The ECU for your car is in the passenger footwell, against the firewall. I would bet your rain issues caused some water damage to your ECU. when you pull back the carpet to look at the ECU, if it is wet, get it dry before installing another.

                    I think I have an extra ECU for test purposes if David doesn't.

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                    • #11
                      Yeap, that's the failure mode. They fault when they get warm, then they crap out completely. Sometimes they crap out without warning.

                      And in the NA6, the ECU is in the passenger side floor, underneath the carpet.

                      And the NA6 uses a thermoswitch to control the fan, not the ECU. All it does it trigger the relay that turns the fan on, ECU isn't involved.

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                      • #13
                        A quick check - Pull your sparkplugs. If it's a coil pack, 1&4 or 2&3 should be fouled to hell and back. * Thinking about it, they're probably all fouled - but one pair should be more fouled than the other.

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                        • #14
                          Update...

                          Finally got around to troubleshooting with the box of parts David was nice enough to lend me. Put a new thermosensor on the back of the engine, no change. Changed the AFM, no difference. The replacement coil packs were all from NA8s or NBs so they wouldn't work. I ordered a new coil from Amazon to try Wednesday as even if the original isn't bad, it has a ton of miles on it. I decided to reinstall the coil for now and swap out the ECU, unfortunately the numbers on the one I pulled from the car don't match the one David let me borrow (his is from a 93 Cali car with sequential fuel injection, mine is a standard B61P 18 881B NA6 ECU). While I had the ECU out of the car, I cracked it open and found some significant corrosion inside. Looks like this is the cause of the issues I'm experiencing... trying to source a good NA6 ECU to confirm.


                          IMG_3683.JPG
                          2004 MSM - FM LE Package, VMAXX Coilovers, 6ULs, Boss Frog Double Hoop
                          2014 Exomotive Exocet - NB2 VVT drivetrain, Xida Coilovers, Enthuza Exhaust

                          Comment


                          • #15
                            Bingo.

                            If you need to get this car moving, I should have a spare NA6 ECU, non Cali.

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