ihatebmw

What’s up guys, I got a 2007 CLK550 Convertible. I have a p0308, cylinder 8 misfire, I’ve recently changed all spark plugs, cylinder 8 coil, even did the swap coil test and it’s still a P0308. I changed the air filters as well if that’s worth mentioning. Car turns on everyday, doesn’t hesitate, runs pretty good. On cold starts I can feel a rough idle. Almost like the car is cammed. But it’s not like a stage 4 cam. Stage 2 at most lol. After it warms up it calms down. But the misfire isn’t like horrible to the point I have drive ability issues or flashing engine light or limp mode. Car drives hard asf as in strongggggg. What could it be? My freeze frame shows that it happened at 1k rpms. So I’m assuming it’s misfiring at idle. I’ve posted on the A209/W209 forums but not a single person responded so hopefully someone here does. Thanks. 149k Miles

tonylinc

Are the spark plugs the right ones for the engine, sometimes people get the wrong ones. For that engine I would use only NGK 4288 (PLKR7A) Laser Platinum, with no substitute or variation. I would remove the one for cylinder 8 and either replace it again or just look at it and see that it has no visible defect. On most of the M273s I have owned I've bought all new coils, they cost at the time, around $30 a piece. Then I kept the old ones, in the garage. Many months later one of the new ones quit working, I got one of the old ones out of the box, used that, and all perfect again. As long as you are sure it is cylinder number 8 I would just buy another new spark plug for that one and put it in, then if it still misfires I'd buy a new coil for that cylinder. STILL a misfire I would buy all new coils. Then if it is still misfiring, I don't know what I would do!