[RandallM]

Time for my two cents.

Hi Steve, I hate to say it, but all Fords ping, or rattle. I don't buy Fords, however, my wife does. She says they last forever. That's becuase she has a nut that loves her and keeps her Fords up and running. Anyway, Fords have some anti-knock circuity that does not last long. As the car gets older it just knocks. The best thing to do is run some seafoam cleaner in your tank. Keep the injectors clean and that's about all you can do. You could lean the motor out some, get a chip to eliminate the ping, but that makes the engine run hotter and lowers engine life.

As for lower octane at higher altitude, less oxygen, less fire you need. My Trooper gets 15 mpg at sea level and 22 mpg in Denver. It's mostly because an engine at sea level develops more power, uses more fuel than one at altitude.

My ex-wife (Chemical Engineer) explained the main difference in octane to me as the higher octance mixes better in the cylinder and detonation occurs with a more even burn. Detonation wave is smoother the higher the octane, while lower octance detonation is more ragged. Higher compression engines work better with higher octane because the fuel needs to be more volatile to evenly mix with all that air packed in.

I guess the reason for lower octane availibilty at higher altitude is your not going to pack as much air into the cylinder and the volitility of the fuel does not have to be so high to thoughly mix with the air.