high compression on stock ecu it's running too lean.

you'll sometimes get an o2 code for too rich/too lean conditions.

an afc might allow you to get extra fuel at idle or low throttle positions, but at wot it won't and will more than likely trip a map code because positive corrections will only increase the map voltage when there is no corresponding portion of a fuel or timing map on a stock ecu beyond 0.2 psi (basically 0in/hg).

socketed/chipped ecu, larger inj, and dyno tuning sounds like what you need.

if you're trying to keep using the afc drop some 310 or 370cc inj.

running on 3 cyl could be way too lean and it running poorly, your cyl pos sensor/dist could have gone bad, or you could have toasted a piston from running too lean.

hope that helps.