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Turbo M20 hard stutter under accel

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    Turbo M20 hard stutter under accel

    Have been trying to figure this out on my own for a bit now but have made 0 progress. Car runs and drives strong but on occasion when making a pull it feels like it completely loses power for a split second then comes back on strong, hard enough to break the tires free. i reviewed the last log with the tuner and he suggested some sort of spark issue. Like a hard misfire? I will post the last log for review. I have gone through all the electrical connections and ensured they are tight. Where do i go from here? troubleshooting steps would be helpful. Car is set up with wasted spark.
    Ok, how do i convert an MSL file to a format i can post on here?

    #2
    Man, I went through something similar for years and finally solved it once I started adjusting the dwell in MS. I had changed from the stock bosch coil to MSD SS Blaster which apparently required more dwell.
    "I'd probably take the E30 M3 in this case just because I love that little car, and how tanky that inline 6 is." - thecj

    85 323i M TECH 1 S52 - ALPINEWEISS/SCHWARZE
    88 M3 - LACHSSILBER/SCHWARZE
    89 M3 - ALPINEWEISS II/M TECH CLOTH-ALCANTARA
    91 M TECHNIC CABRIO TURBO - MACAOBLAU/M TECH CLOTH-LEATHER

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      #3
      I almost wondering if I'm losing a fuel pump? It acting as if it loses fuel for a fraction of a second then slams back on.

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        #4
        I almost wondering if I'm losing a fuel pump? It acting as if it loses fuel for a fraction of a second then slams back on.

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          #5
          doesn't sound like fuel pump issue if it completely loses power for a split second as it would likely be more gradual. Are the coils still getting power when it "cuts out"?
          89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

          new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

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            #6
            Good point,
            not sure I know how to tell if the coils lose power when it happens. Still very new to reading data logs.
            The 1 major thing I see is when it does cut out is a large spike super lean in afrs.
            If someone want to explain how to convert msl data to something r3v friendly I'll post up the last pull for review
            thanks all!

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              #7
              Rig up a test light on coil 12v power feed that’s how I found an intermittent ignition issue
              89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

              new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

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                #8
                give us a google drive link, https://ufile.io/, or similar.

                I'm gonna guess it's a fueling issue if you only have problems when you accelerate
                '84 318i M10B18 147- Safari Beige
                NA: 93whp/90ftlbs, MS2E w/ LC, 2-Step
                Turbo: ?whp/?ftlbs, MS3x flex @ 17psi

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                  #9
                  After work I will sit down and upload a log.
                  it's not all the time. Very intermittent. Has to be under flat foot accel. Most of the time 2nd or 3rd gear.
                  I'll get started on rigging up a test light as well. Cant have enough to find a root cause.

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                    #10
                    would it be a big missfire or literally 100% power cut/shutoff? any effect on tach signal or other other things on dash/cluster?
                    89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

                    new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

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                      #11
                      Nothing going on with any other part of the car. Tach Speedo coolant lights all of it remains solid.

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                        #12
                        Any chance you're hitting the over-boost protection? If it's a fuel issue, you'll likely see lean in your data logs, if it's spark, it'll run rich. Depends how transient the event is, may be hard to capture if it's really quick, but if there's a sustained period of break-up you can probably trust the AFR readings. May be worth putting the fuel in open loop while you're debugging so that the ECU isn't trying to correct the fueling and masking the issue.

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                          #13
                          Originally posted by citizen_insane View Post
                          Any chance you're hitting the over-boost protection? If it's a fuel issue, you'll likely see lean in your data logs, if it's spark, it'll run rich. Depends how transient the event is, may be hard to capture if it's really quick, but if there's a sustained period of break-up you can probably trust the AFR readings. May be worth putting the fuel in open loop while you're debugging so that the ECU isn't trying to correct the fueling and masking the issue.
                          I thought the same thing immediately, cooler weather denser air, gotta be boost cut..... Nope. 200.7 kpa max. Boost cut set for 238 kpa. But to your point.... In the log when the event occurs it spikes to max afr or there about. I'm either drowning it in fuel due to spark problems. Or the fuel system is not keeping up or.... I'm losing electrical power to either system. I've only read briefly that drowning an 02 in fuel will give a false positive to lean. Not sure?
                          I'm tuned solely on open loop. My ecu has not been tuned/ given authority to make changes. Only have 1000mi on this new motor.

                          Tune was done on steady state dyno. Never made a hiccup

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                            #14
                            If you get a misfire you'll get a heap of unburnt air and raw fuel in the exhaust. Unburnt air = 02 sensor reports lean condition.

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                              #15
                              https://drive.google.com/file/d/1j2s...w?usp=drivesdk

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