My 1988 Volvo 245 DL failed the Nox portion of the emissions test. I have replaced from the exhaust manifold back, so headpipe, cat, resonator, muffler and all hangers and pipes. The nox reading ended up being 2764. I replace the pcv pipe and plastic piece, check and replaced most of if not all vacuum lines. I then replaced the cap, rotor, and spark plugs and drove the car for 70 miles and had it re-tested right after driving for 70 miles and the Nox reading came out at 2143. I have also checked the whole exhaust for any leaks more then twice. I don’t think that the O2 sensor is bad because all the other reading from the emission dropped by 40% or more after all the above stuff was completed. Does anyone have any other ideas on what to do?

I bought the car for $700 and the guy showed me repair record going back for the last 8 years. So I took his work on a lot of the work that was done to it. I’m finding out that most of the work done to the car is pour at best. Just a side note!