So my 2008 Infiniti G35xs 170,000km is misfiring and the exhaust sounds like there is a thud in it and the car feels like there’s a thud under it as well and when I’m driving it’s really rough ride and the idle is rough as well I ran a code and it was showing me cylinder 4 and I recently had changed spark plugs so I changed the coil and the problem still priests I’m thinking it is the fuel injector but Someone has also told me that the motor could be going so if anyone had any insight or had the same problem please share and let me know.

 

Pull and inspect your plugs. Doesn't matter how new they are, pull and inspect them.

 

I had similar issues awhile back. I ended up changing plugs and new ignition coils. Got a good deal from CARID.COM on the coils. Ended up putting NGK plugs and coils. Also changed PCV valve. Cleaned both air mass sensors and cleaned both throttle bodies...Had no issues since then car is running like new