benz_addict

I'm still suffering, got it diagnosed from the dealer they said check for timing. They checked for timing but saw it was spot on. Plugs, coils, wires have been swapped already. No luck. Lifters seem fine too, no broken springs or any lose rockers.

I'm running no cats so can't be a clogged cat? BUT I do have a dual X muffler could it be a clog in there somewhere? Dealership wasn't able to check for this.

Still showing CEL misfiring P0300, 305 to 308. No other codes. This is a very mysterious weird problem I honestly believe there's something wrong with the harness somewhere perhaps under the supercharger or exhaust manifold gasket is gone because there is a loud ticking noise coming from that side. I'll be replacing the header gasket anyway. If problem doesn't go away then maybe it's time to get rid of her. There's a very low mileage CLS55 that's very tempting here... hmm.

s4treg

Coming from a Porsche, misfiring, and ticking of the engine would sometimes represent piston slap. Before getting to that though, have you checked compression on those cylinders? You could be misfiring due to lack of compression. It's a pretty simple test and should start to rule things in or out.

if you have low compression, you have a leak somewhere...it could be at the header... valves, lifters... OR it's low, which could mean head gasket or bad piston rings, scoring of the cylinder.

I know this is all a lot, so if you can start with a compression test, if that's good then you are back to your trying to figure out plugs, packs, wires, etc.

Hope that helps.

abrim

This may have been your first thing to try, but I recently had the same problem and replaced the o2 sensor and now she drives like new! Had 14 codes appear!! Swapped out the o2 and now it's fine

s4treg

O2 sensor would be a hell of a lot better than what I was point towards. Of course my experience with this issue was with a Cayenne Turbo. Google piston slap for Porsche...you'll find a lot. I would advise that you not dive into a head gasket replacement though until you do a compression and leak down test. But I've seen your other posts, you seem to know your sh$t anyway.

benz_addict

I will swap the swap the upstream O2's left to right. Even though left O2 is new
after leak down test will come

thanks

bobgodd

How did you change out the coils, with brand new ones?