Misfiring - Codes P0300, 302, 303, 304
Thread Starter
Member
Joined: Sep 2012
Posts: 217
Likes: 19
From: Chicago, IL
2003 CLK500, 2003 CLK55, 2008 CLK550
Misfiring - Codes P0300, 302, 303, 304
So, some more information to help you help me.
Car: 2003 CLK500
Miles: 42k
I noticed the car started to run funny, and then the check engine light came on. It felt like a misfire, and was later confirmed by the codes. Since it is all on one bank of cylinders, I am thinking this is not a bad MAF, which is what I assumed it was at first. I also just filled up, and thought maybe it was the gas. Although, all of the misfires being on one side again points to something else.
In addition, I have been noticing a rattling noise. I was at the dealer one day, and they said it was most likely an exhaust mount that is welded to the exhaust making the noise. However, with the current misfires, I am thinking there is a good chance that one of the cats on the passenger side is shot.
Just wanted to get your guys opinion on this. Is there other things I can check before getting the cats changed? Also, is it usually the primary or the secondary cats? Is there a good way to tell?
Also, if anybody reading this is from the Chicago area, can you recommend a good shop to have the work done at? If I do have to replace the cats, I would really prefer to put in high flow ones. If I am going to have work done, I want something to show for it!!!
Thanks in advance!!
Car: 2003 CLK500
Miles: 42k
I noticed the car started to run funny, and then the check engine light came on. It felt like a misfire, and was later confirmed by the codes. Since it is all on one bank of cylinders, I am thinking this is not a bad MAF, which is what I assumed it was at first. I also just filled up, and thought maybe it was the gas. Although, all of the misfires being on one side again points to something else.
In addition, I have been noticing a rattling noise. I was at the dealer one day, and they said it was most likely an exhaust mount that is welded to the exhaust making the noise. However, with the current misfires, I am thinking there is a good chance that one of the cats on the passenger side is shot.
Just wanted to get your guys opinion on this. Is there other things I can check before getting the cats changed? Also, is it usually the primary or the secondary cats? Is there a good way to tell?
Also, if anybody reading this is from the Chicago area, can you recommend a good shop to have the work done at? If I do have to replace the cats, I would really prefer to put in high flow ones. If I am going to have work done, I want something to show for it!!!
Thanks in advance!!
MBworld Guru
Joined: Dec 2009
Posts: 10,782
Likes: 1,011
NO LONGER ACTIVE
Your mileage is quite low for bad cats. Usually they 100K miles or more. This could be a fuel deliver problem, or a bad wiring harness to the right bank. I'd look at that before going for new cats.
Thread Starter
Member
Joined: Sep 2012
Posts: 217
Likes: 19
From: Chicago, IL
2003 CLK500, 2003 CLK55, 2008 CLK550
Just to close out this thread, it was one of the secondary cats that was bad. The material separated from the pipe and was rattling inside the piping. It was able to rotate inside the piping, so it was rotating sideways and causing a huge restriction in flow, causing the misfire. Hopefully anybody having a similar problem in the future can find this thread useful.
Mods can close this if they would like.
Mods can close this if they would like.
