Dropped the wife off at the Orlando airport, was in a bit of a rush and was driving between 70 and 75, no other cars on the road. Without A/C, I traveled 310.2 miles on the highway with 5.33 gallons (57.8mpg).
On the way back I had close to 5 hours to learn how lean burn works in this car.
Here's leanburn engaged when cruising at around 68:
Approximately every minute to minute and 25 seconds, it drops out of lean burn to purge NOx from the cat. Without moving the pedal position, this is what happens when it drops out of lean burn, cruising in 5th at around 68mph:
For a while I couldn't figure out how to reliably get lean burn to engage. I was expecting it to enable itself when cruising, but it never happened on the highway. At ~65mph, the instantaneous readout gives approximately 50-55mpg, but letting off the gas quickly until it reads about 100 (not far enough to cause fuel cutoff), and then pushing the pedal back to the position it was at before, results in lean burn engaging reliably and consistently, with around 70-75mpg being the minimum economy possible with lean burn engaged. Any lower and it drops back to normal burn.
After engaging lean burn, and driving with load with the maximum throttle position while still maintaining lean burn (~75mpg), I found I would maintain about 58mph on level ground while missing two aero panels and with the wrong tires. On hills, the car slows down to as low as ~48, and speeds up to maybe 65 on the downslope. HOWEVER, I came up with an interesting trick which plenty of others have probably already discovered - a sort of IMA pulse and glide to maximize lean burn. Here's how it works:
The computer cycles the engine out of lean burn every minute to minute and a half with a constant throttle position, and keeps it there for around 5-10 seconds, at least under the driving conditions I had today. I decided to try giving it just a hair more throttle when it dropped out of lean burn, enough to get 4-5 bars of assist, and then put it back into lean burn after ~10 seconds by letting off the pedal until I saw 100mpg and then pressing it back down until I saw ~75. It's also possible to override the NOx cycle and put it immediately back into LB, but I don't want to ruin my cats. Anywho, with this method, I was able to achieve
70.2mpg with an average speed of 68mph, or in other words, ~7% less fuel economy than leaving lean burn engaged with a 17% higher speed. The trickle charge when in "glide" was enough to keep the battery topped off, and I never saw the meter move or any charging bars.
It occurs to me that I should check the spare tire and see if it's a Potenza. If so, I'll put the Potenza that's on the passenger rear, and the spare, in the front where most of the weight is. That, plus replacing the aero panels should net me a significant improvement.