Misfire on cylinder #4 - 2002 ML320
 

A friend's 02 ML320 has a misfire on cylinder #4, per the code. I did the typical steps when you have only one cylinder misfiring... swap coils/wires and it stayed on #4. This same thing happened about 9 months ago and after replacing the spark plugs it ran better all up until just a few days ago. Same problem. I'm going to change the plugs again tonight to see if it runs better again, but either way I need to figure out what's going on.

Any ideas? Has anyone had trouble like this before and it be a computer or wiring?

Waste of time and money. Just remove plugs 4 & 5 and compare them.

What brand name plugs and part # did he use?

I don't remember what they were. He's coming over tonight and he already has plugs but I'll compare them first. Sure hope its not a valve or rings, but it took so long to happen again its weird. I forgot to mention it has 123k miles, just getting broken in.