Quote:
Originally Posted by Wepeel
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 was told that GM does two calibration for their spark one for high octane and one for very low octane and based on the knock frequency and severity the ecu estimates an octane number and interpolated between the two spark surfaces. Not sure if this applies to all engines and not sure if they still do it