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Knock Sensor wave forms during missfire events


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If I'm looking at attempting some mathematics to try to get the ECU to at least flag when a potential missfire happened.. Or at least some way to Stare at a Log of Trigger vs Ignition event VS Knock sensor.

Is the x Series "quick" enough to show enough resolution to detect a missfire? Or Would you need to be looking at a change in the Knock sensor waveform? Issue wouldn't be a Dropped cylinder, That should be realtively Obvious via a Knock sensor... Its one that's "sorta" firing.

(On the Standard Subaru ECU its apparently detecting the slight change in motor speed of a missfire.. Yeah, That's too hard for me to figure out!)


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It would need a dedicated firmware function to do this.  Generally they look at crankshaft acceleration through a certain angle window and compare to the other cylinders over the same cycle.  Some use a feed back signal from the ignition coil.  You wouldnt be able to do it with user math as it needs to be synchronous, in our ECU's all synchronous calcs are done with a dedicated "eTPU".  I doubt the subaru system works reliably as the 36-2-2-2 crank wheel is a bit too low resolution to start with and has some big patches of missing teeth which gives even less resolution.  Maybe at cruise RPM it would work ok.  Nearly all engines that do misfire detection well have a 60-2 crank wheel. 

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