Mobile mechanical services

1993 Skyline R32 has had G4+ fitted. Spark plugs are not lasting long, very fuel fouled, (getting the vehicle ready for certification) while fitting heat shields I noticed the o2 has been removed an plugged. I said it needs to be put back, his reply was, everyone he has talked to says the G4+ does not like the o2 being there or something to that effect. Owner said he disconnected a three wire (not shielded) connector which I can see, I also see a shielded two wire connector, so can I have the official word on what the G4+ o2 sensor is before I spend time on it. Thanks Terry