[gone-ot]

That is NORMAL "closed-loop" operation.

During "closed-loop" operation, the computer constantly adjusts fuel quantity so as to MAINTAIN a perfect "stoichiometric" 14.7:1 A/F, and only allows the engine to go richer when almost wide-open throttle (WOT) input from the driver is detected (plus a few 'other' unique situations).

Part of the *reason* for this 'stoich' operation is the catalytic converter(s) need something to "burn" and this 14:7 A/F-ratio provides that minute amount of gasoline. The "lean best burn" A/F-ratio for maximum fuel economy is something like 16-18:1 A/F-ratio, so obviously today's engines are NOT getting anywhere near the FE that the older (pre-EPA) engines could, and nowhere what they COULD get if EPA regulations weren't so obsurd.

In fact, the Honda HFE engines, which routinely operated in this "lean-burn" region (16-18 or more A/F) to achieve excellent FE are nolonger permitted because of their NOx emissions while in "lean-burn."