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Originally Posted by sperry
I've heard the ol' STi popcorn machine coming from MattR's hood too on a bad tank of gas as well. However, I think that's an extreme case caused by a large change in parameters as seen by the ECU: i.e. the ECU can't instantly adapt to the sudden appearance of low octane fuel.
Under normal conditions, a car running up near knock will properly adapt and avoid audible pinging as the temperature increases, or as the humidity changes, etc, even on a highly tuned car. In fact, if you were to gradually lower your octane by adding 87 to the car a gallon every 50 miles or so, you'd probably be able to under-tune the car to run on that swill... assuming you don't mind a motor that makes no power. 
As was mentioned, and as I found out the hard way, the ECU unfortunately can't react to anything above 6k rpm. Which is probably a contributing factor to why I spun a bearing when my car knocked at 7000 rpm at the last Lovelock Club Trials. But below that threshold, the ECU does a very good job at protecting the car under dynamic circumstances. |
OK, I rephrase my statement that under normal conditions, you should never hear the knock.
Now if your tune has the timing map so far advanced or the fuel so lean such that the ECU isn't permitted to pull enough timing to compensate, then don't blame it on the knock sensor.
I would think load would drop off significantly above 6K, so knock should not be an issue as timing should have been pulled as you went through the higher load RPMs unless you do a big downshift right before increasing load. I guess if you are leaning out at high RPMs due to fuel starvation, that might contribute to it. But again, that would be a map problem, not a knock sensor problem.
Oh, and before you jump all over me, I don't think lean fuel mix directly generates detonation, but the increased combustion chamber temperatures as the mix leans out certianly do.