I have a 2003 Nissan 350z changed the valve cover gasket and spark plugs. Prior to this the car had a little misfire but not to bad, after the valve covers and new spark plugs were changed the car started misfiring bad checked the car and 1 spark plug was bad so installed a new one and it’s a little better but no one can tell what’s causing the random misfire
What misfire codes are you getting?
Are you using good quality NGK or Denso plugs or some Chinese knockoffs?
Well we'll start with number one once you change the spark plugs you have to take the ignition coils off of each plug their plastic and many times they get damaged and it can easily be the coils have been damaged or the wiring that feeds them. If you find a mechanic like me he can put on a scan tool that's very fancy drive it till it misfires then analyze it it shows which cylinders misfiring and how often then you can find exactly what's causing it
