Lean burn when not quite warmed up

[RobertSmalls]

Once the car has been warmed up, you can lean burn down to 75mpg in 5th gear, and the ScanGauge will show LBN=0. At the other end of the spectrum, while the engine is cold, you will not lean burn, and LBN=85 or so. This thread is about what happens in between those extremes.

After a few minutes of operation, under light load (~80+mpg), you'll begin to see LBN values between 10 and 50. I presume this represents running slightly lean of stoichiometric. This isn't lean burn "mode", and there's no sudden loss of power or lurching on returning to LBN=85.

After another minute or so, you'll first see LBN=0. But this is "shy lean burn mode", as I call it, because it used to be very hard for me to hold it. The trick is, you can't drop below 100mpg in this mode, or it will fall back to LBN=85. Give it another two minutes before asking for 75mpg.

I've also seen "shy lean burn mode" upon transitioning from <50mph driving to a 70mph expressway. It takes a few minutes more before you can do 75mpg lean burn.

I used to see lean burn become available at exactly the same spot on the highways I drive regularly, but by spending as much time as possible with the LBN gauge < 50, I've been able to lean burn at 75mpg a mile sooner, with obvious FE results.

This information is probably more useful to MIMA users, who are able to add assist to keep mpg > 100 while the car is warming up.