Comment Re:MPG and GPM are both useful (Score 1) 1042
Lots of things can increase the tendency to knock.
Lean fuel-air mixture (which is common these days in efforts to improve emissions and mileage)
High load (due to towing, steep grade, heavy acceleration, high speed, etc)
High ambient air temperature
Too high heat range of spark plugs (which may happen when auto makers are trying to improve warm-up times for emissions purposes)
Too much boost in a forced induction system
I happen to live near a freeway (traffic commonly moving at 70+ MPH) that has a steep grade and summer temps over 100F (which means that air conditioning is adding to the engine load too). Knock can be a serious issue.