StevieC, you mention the O2 kit so that you don't run lean, but you're injecting a stoich mixture of hydrogen and oxygen, so how would that affect the O2 readings? I went around and around with a guy here at the office about these kits until he mentioned screwing around with the O2 readings, then everything made sense! Gasoline is most efficient at 17-20:1, not at 14.7:1 like most cars run, so by screwing with the O2 readings, you can actually lean the car out and make it more efficient, as well as sending NOx emissions through the roof. I wouldn't suggest taking it in for an inspection if they hook up to the tailpipe where you're at.