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'07 Cobalt LS, 2.2 L I-4

Car is not getting a misfire code. (p030x) However, the mode 6 data shows Non-zero "misfire counts" on all cylinders. The counts are single- or double-digits, and are very low at highway speed. I don't feel any misfires, and I'm not aware of a performance problem.

  1. Should these counts be just dead-nuts 0?
  2. Is misfire detection reliable at high speed?
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You're raised two questions:

Should these counts be just dead-nuts 0?

In my experience, NO. While I'm sure every manufacturer has their own standard for when to set the CEL on a misfire, some number of misfires are "normal".

Is misfire detection reliable at high speed?

The speed of an automobile engine compared to the speed of the electronics monitoring and controlling it are at least an order of magnitude apart. So yes, even at the engine speeds used in F1 engines (~20K RPM) misfire is detected and controlled.

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  • Something which could be done here is to clear the ECU memory, which should reset the misfire count. One never knows what the count is over time ... at least I don't think that is easily discernable. Not sure how long the misfire information stays stored for any given vehicle, but the number may have collected over a great period of time. Clearing the misfire count might give someone a good idea of how often it is actually occurring.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Feb 27, 2023 at 18:04
  • Thanks for your answer. When you wrote "in my experience", can you explain a little of what your experience entails? That way we know if you're a hobbyist, mechanic, etc. (Also, you may want to define CEL for those who don't know.) Thanks!
    – Amazon Dies In Darkness
    Commented Feb 27, 2023 at 21:16
  • @Pᴀᴜʟsᴛᴇʀ2 Good idea, just don't do it right before a smog test, as the car needs driving to collect data. Learned that one the hard way, '94 car I had pulled the battery and driven it lightly prior to smog, so it had never seen wide-open throttle on the TPS.
    – Harper - Reinstate Monica
    Commented Feb 28, 2023 at 4:27

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