yes a bad plug wire can cause a dirty sooty spark plug, also a wide band o2, will tell the computer that the AFR is lean when there is a misfiring cylinder

1968 Charger COLD A/C Hilborn EFI
512ci 9.7 compression, Stealth heads, 4.10 gear A518 ODtrans 4100lb,10.93 full street car trim
2020 T/A 392 Stock 11.79 @ 114.5