Ok this post has gone far enough I think and is becoming a bigger deal than it really is. As others have said if you want to "test" if it is pre ignition there are stations in California that will sell 100+ Lead free octane, it's super expensive but if you just want a test to confirm it will work. If it is pre ignition the pcm will not "learn" and adjust long term fuel trim for it, fuel trim is strictly an adjustment based on AF sensor feedback. PCM won't "learn" a timing advance, they have a base table with modifiers based on IAT/ECT and other variables but will always try to go to that "calculated" base timing, if severe enough knock is detected it will reduce timing to a certain degree determined by another table and then creep back to the calculated base map when the condition is no longer present. It will keep doing this dance and is constantly fluctuating much more rapidly than any LTFT.
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