Originally Posted by Deathscort
since its EFI, the increased voltage load retards the ignition timing.
I'm afraid it's not that simple.
It might slightly retard the timing to compensate for decreased vacuum caused by increased throttle angle. It has to in order to maintain correct timing.
The retarded timing isn't the issue. The issue is slightly increased load imposed by the alternator and subsequent slightly increased fuel consumption. And charging system voltage in itself has absolutely nothing
to do with ignition timing.