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Originally Posted by Wepeel
I feel like I should search all posts by arghx7 just so I can thank them all.
One thing I've always wondered - the sensitivity of the knock sensor. I'm guessing there's a whole discipline associated with interpreting knock accelerometers and determining what is "true" knock vs. what is something that might indicate knock vs. when conditions are favorable for knock. There must be some spectrum - our ECUs are designed to pull intervals of timing and it needs to know whether to pull 1 degrees, or 4 degrees... maybe that has to do more with the frequency of knock signal versus the severity, or maybe both.
Also, I've heard tuners say that they've driven around with detcans and can't hear any knock even though the ECU is pulling timing. I know there were some recent findings with the WRX/STI platform that suggested that the ECU could pull timing (can't remember if it was FBKC or FLKC) just based on rapid tip in - maybe rate of throttle opening or pedal position change - something like a preemptive knock control. I know for sure GM had this programmed into their ECU for some cars.
And then there are the cars that can run on regular or premium, where running regular is not a detriment to the engine but premium will have more performance. Not sure if there is a fuel sensor, like the flex-fuel kits for our cars, or if they are relying on knock signals to determine fuel grade. If it was the latter, it doesn't seem like driving the engine to knock would be a great strategy for determining fuel grade, but it would make more sense if the knock sensor got a little "noisier" with lower octane fuel but the engine wasn't necessarily knocking.
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I think there is are tables in the rom where you can program in the "tip in" ignition retard according to the amount of change in throttle position and another table that control the amount of additional fuel is added at tip in according to the percentage change in throttle.
I'm also curious about this tip in knock that the ECU is detecting particularly at higher temp operation. It seem like it's impossible to totally eliminate nomatter what you do with the tip in enrichment or ignition retard. Yet, it seems to disappear when temperatures cool.