Thanks to DAX for sending me the OBD training manuals. I'm on part 2 of PGMFI System Overview. I found this nice piece of info, I think it refers to the D15Z1:
"Certain Civic Models use a very special O2 sensor called a Lean Air Fuel Sensor. This sensor has 5 wires and can be controlled by the ECM to run the engine on A/F ratios as lean as 23:1"
That's my future engine all right I'm hoping to run 23:1 on a few road trips this summer