Originally Posted by rob-2
I believe you're right. I use cruise control for nearly all my freeway. Just thought the motor with low/no boost would burn leaner. I'm sure the eco map will pick a few MPG's up and that will offset my heavy footed fun
Your car stays in closed loop mode up to about 50-55 g/s on the MAF reading. In closed loop, your car will always target stoich so it will burn as ideal as possible.
I looked at my datalogs for you and in 5th gear at around 2800-2900 RPM, my WGDC is at 0% (I tuned it for this) and at 17-18% throttle I'm at -3.5 PSI vacuum, still closed loop at about 40g/s.
At 22% throttle, I'm in boost at about 2PSI, still 0% WGDC and I've just dipped into open loop at 63g/s.
So really, for fuel economy reasons, the question is... are you able to maintain 80MPH with less than 22% throttle? From looking at my logs, it appears that at 22% throttle I'm actually accelerating, very, very slightly, and at 17-18% throttle, I'm maintaining RPMs so I'm cruising.
But that's just to give you an idea of how thin of a line you'll be toeing between open/closed loop even with 0% WGDC dialed in.