I've always known that a stone cold engine runs richer and in the winter, richer for the longer warmup, accounting for part of the lower winter MPG we're all used to.

So one thing I was wondering was this: What would engine operation / fuel efficiency be like if you only measured it from the point that the engine was hot?

Blends of gasoline can vary significantly and the mix of compounds is complex ...

Wikipedia: Gasoline

but I was wondering if we could make a fairly comprehensive list of different factors and changes in instrumentation that account for most of the difference in fuel economy we see.

So, my questions:

When the ACT sensor reads inlet air that's 40 degrees (30 vs 70) colder, what does the PCM do in response?

Anything happen to the spark advance table, or is that static?

Does the adaptive fuel table get re-arranged, and if so how?

As a general rule I've read that colder air charge means more power, but other things being equal, how does the colder air change the character of the burn in the combustion chamber, and how is that likely to be read by the HEGO sensors? Resulting in what likely adjustment?

"Winter Blend" typically has less heat content per gallon, partially because of added oxygenates, but also because of other non-gas additives. Lots of this stuff accommodates cold start operation, but it leaves me wondering how the engine would run when hot if operated in the winter on summer blend gasoline?

My interest is mostly in how the more recent fuel injected versions of this engine react to these factors.

 

?? really? I could tell, but then..........