The first video at
http://ecomodder.com/forum/showthrea...ions-8629.html mentions that the computer will enrich the mixture now and then to regenerate the catalytic converter. This behavior would obviously involve exiting lean burn. I'm not sure if your cat is of the same type, but if so, you'll want to decide whether the occasional fuel dump is required to keep your cat alive. Find out, because IIRC, your cat costs buckets of ducats.
I'll watch this thread with interest, since I hope to join the lean burn club soon.