07-16-2015, 11:59 AM
It wasn't so much the altitude change as the octane. Motor fuel sold in higher elevations has a lower octane rating (here in the Western U.S.). With less power being generated at high alitudes, an engine that uses regular grade 87 octane at sea level will do just fine with 85 octane at 7,000 ft. The problem arises when you ride down to lower elevations with that 85 octane fuel. To add to the problem, heat will exacerbate the problem and it was about 110F (43.33C) when I rolled into Phoenix.
I prefer the term detonation because it describes the premature explosion of the air/fuel mixture, commonly due excessive pressure and temperature on the compression stroke. It's different in origin (and often confused with) pre-ignition, which will cause the same ping/knock/plink noise, but is caused by a hot spot somewhere in the cylinder. Octane will fix the former, but not the latter.
I prefer the term detonation because it describes the premature explosion of the air/fuel mixture, commonly due excessive pressure and temperature on the compression stroke. It's different in origin (and often confused with) pre-ignition, which will cause the same ping/knock/plink noise, but is caused by a hot spot somewhere in the cylinder. Octane will fix the former, but not the latter.