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Thread: 2014 Sonic RS high RPM misfire, I've tried everything

  1. #1
    Tuner in Training
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    2014 Sonic RS high RPM misfire, I've tried everything

    Hello. I recently bought a 2014 Sonic manual transmission. Vehicle came with ZZP exhaust and downpipe, ZZP intercooler and bigger throttle body, ZZP thermostat and a ZZP tune. With this and any tune that I've uploaded that is not factory, it starts a misfire at around 5500 rpm under high boost and full throttle. Under 50% throttle or less, it runs fine. If it starts to misfire and I don't release the throttle, I get the infamous check engine light blinking and traction light. I replaced the valve cover and PCV hose thinking it had a leak, but it didn't fix it. I installed new AC Delco original plugs and NGK iridium plugs, gapped them at .027, .024, .020 and same result. I installed a ZZP coil, no fix. I messed with the tune, changed a lot of parameters, retarded and advanced timing, changed PE, nothing. I also messed with wastegate DC and knock airmass, same thing.If I upload a stock tune from a 2013 Sonic (leaving the transmission settings the same as the ZZP tune since I don't have the stock tune), then it won't misfire. I'm running out of ideas. I'm surprised that the ZZP tune isn't running good since they're a very reputable company. Please help 🙏. I attached tune and a second gear pull log. Thank you
    Attached Files Attached Files

  2. #2
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    I've been doing an unhealthy amount of reading on this issue from the forums here and all over the internet for days. Even after reading and testing for weeks, I can't figure it out

  3. #3
    Tuning Addict blindsquirrel's Avatar
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    So is it misfiring because it's lean, or showing up as lean because of a misfire?

  4. #4
    Advanced Tuner
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    The log indicates the MAF does not increase after 5000 RPM with WOT. Is the turbo worn out. Check for shaft play. Im not a tuner.

  5. #5
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    I haven't installed the wideband yet, but I don't suspect fueling. Afr commanded is 11.88, and is on stock turbo and stock injectors. I sense it's valve float or tune related.

    As far as turbo goes, I'm not sure what the condition is. The car has 77000 miles and I'm not sure if it's been replaced yet, since I bought the car a couple of months ago. I took out the intake the other day to inspect turbo, but it had very little shaft play, seems like a normal amount. I don't know if it's burning oil, but my oil level is always consistent. While reading over my own post, I had an idea, kind of like a revelation lol. I'm messing around with accel threshold under dfco, almost at the bottom left. I believe this is how the ECU starts closing the throttle body slowly before redline, closing more and more as the RPM is near redline. I increased numbers from 5000 rpm and up, and it feels like it's getting better, but I'll keep testing.

  6. #6
    Potential Tuner
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    The misfires and lack of acceleration/laydown feeling is most likely due to the high boost holding the valves open at that RPM (well known problem). This will cause all sorts of codes. I did the same, but ended up lowering the high rpm boost levels and it helps but does not solve the problem. The only other option is to lower shift points a bit and tune for torque.
    Hope this helps some.

  7. #7
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    I had missfire when the ignition coil started to get older and older. I saw this many times. Did you change that?

  8. #8
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    Thanks y'all. I did change the ignition coil, I got a ZZP coil. Didn't fix the issue. I'm almost certain that the issue is boost on the top RPM range, and I did adjust accel threshold to start closing the throttle sooner, it helped, but not 100% fixed yet. I'm going to adjust it a bit more, but I'm waiting on a second ZZP coil as the first one had a defect. They took care of it ASAP