u/Working_Basis609

hey team, ‘97 e36 m3. Bought it without smog for a deal price, replaced cracked cat but still didn’t pass (NOX too high), then replaced spark plugs because cyl6’s was black from carbon / misfires and it passed with flying colors.

thought all was good for this round of smog but it just failed again, NOX too high. When i pulled the spark plugs cyl6 showed signs of misfiring again…

there’s no engine lights and it delivers power smoothly with no sputters.

what would cause this specific spark plug to misfire / what should i address next?