Why can't I run as much spark at high or low Kpa's as I can in the middle Kpa's?

 

That's more of a question related to the mechanical side of the engine, but since an ECM can detect where the engine is operating, it can also help it like a mechanical ditributor never could. The lighter the load (low KPA) ususally means that the engine is coasting or some other lean mixture mode and also that it's at lower engine speeds. This means you can run higher advance in order to burn all the fuel charge as it is less volatile. The opposite is true for high load: more fuel, more volatile, and less time to burn it. Very general statement here so take it FWIW.

 

General, yes. But I understand now. I was just curious.