Sorry mate, I was half asleep for some reason I thought you said rich on no1 so I thought gunk in the inlet donut on that cylinder ( the donut shaped plenum runner thing) restricting flow. Now I'm properly awake lol. The non genuine sensor may be a shorter length therefore giving a different reading. May also be screwed in too tight or loose. Seeing as it wouldn't cost anything to check that Id check that first. Did this error coincide with the injector clean? He may have accidentally dislodged a pile of sh*t in that injector that clogged it up once running? If you decide to replace them send me a PM, my stockers are floating around in the shed. Dont stress though. These Barra's seem to be able to take an absolute flogging! Best of luck again