I have a 93 civic coupe with a d16z6 and I can't pass emissions. I just bought the car for 300 from a friend and the only thing that was wrong with it tps and I replaced that. It ran hc .72 out of 1.00 the NOX ran 1.20 out of 2.50 and my CO ran 12.12 out of 12.00. I'm lost on what could be causing this.. The motor has been rebuilt about 50 thousand miles ago and I have all the receipts for the rebuild. I've put new cap, rotor, dizzy, wires, plugs, and the cat was replaced about 8 months ago. I was told that running denatured alcohol would make the car run cleaner and i have used it in my 73 dart and it does help but on this car it made it worse. It brought my HG to .92, CO raised to 12.90 and nox went to 1.32.... I'm new to the honda game and would appreciate any help! If you need any more info please ask.