[19bonestock88]

That’s my theory, and it doesn’t always detect when I EOC, going up to 120-150mpg instead of 999.9... when I first got the car it would throw an O2 related code, and shortly after fixing the misfire it would throw a catalyst efficiency code, but now it throws neither...

I think I’d like to replace at least my upstream O2, or if I hold out until I replace/upgrade the exhaust(starting with header and going all the way to rear bumper), replace both and delete the cat...