Here is a screen-shot of some of the (stock) DFCO calibrations on my 1991 Chevy Truck.
link for larger photo:
http://i702.photobucket.com/albums/w...FCOscreen1.jpg
Note that the factory calibrations shown are not very aggressive at all, and during normal driving conditions it is rare for DFCO to engage.
Also, DFCO and DECEL-enleanment are two completely different things.
DECEL-enleanment commands leaner than stoich AFRs during most deceleration conditions, but only functions when in open-loop mode.
Though it is very wasteful of fuel, closed-loop mode maintains a 14.6:1 AFR during deceleration conditions unless DFCO is engaged.