i have a 93 civic lx (engine = D15B7) that was not manufactured with
an EGR valve, which is weird to me cause i thought all modern
vehicles had one (since the late 70's). I failed california smog 4
times with twice the legal limits of NOX but everything else was fine,
i'm assuming the catalytic converter is the only thing that fixes this
right, as it is likely a 3-way cat?

also does anyone know is using a PCV catch can (oil catch can) is smog
legal in california? i know they are sticklers when it comes to
anything emissions related, as most things need to have a CARB
approved # stamped on them, but since the catch can only catches the
oil and does not stop the air from recirculating and burning up as
intended i dont see why it would be illegal, lowers emissions right?

i know high nox is due to high combustion chamber temps, besides
de-carbonizing the piston tops what else would lower nox on a non egr
vehicle?