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Not to add to the confusion but if I have a say in this,I would vote for the alternator enabled for all runs and hope that the voltage regulator plays a fair game for all runs.
When the alternator is disabled and you start with a freshly charged battery,the fuel pump is running at a higher output,using more amps,producing higher fuel rail pressure and the car could run a tad richer than in later runs where the battery voltage is sagging and the fuel pump output is significantly less than with a fresh battery! ( think of how the headlights dim with sagging voltage).
I realize your car has fuel pressure regulator and the ECU has control over fine tuning fuel ratio but it still has an effect.
Story: Modern vehicles actually use this method as a desperate attempt when something goes wrong. I worked on a GMC Yukon recently (forgot year) that ran rough on a cold start. Long story short it thought that the fuel alcohol content was 87% so the PCM richened the mixture and then it was fun to watch the fuel pump control module dropping the pressure from a steady 55psi down to 45psi as an attempt to achieve the correct ratio. Reprogrammed it for 10% ethanol and problem was gone.(and fuel pressure back at 55psi).
Just my opinion!
Barna
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