[BernardFarquart]

My 2003 E320 has 102K miles on it, and has been making a "clicking/rattle" sound that I recognized as the catalyst. I have had cars make this noise for some time prior to failure, so although I was not pleased, I figured I had awhile to deal with it. after making some noise (usually at start up & taking off from a stop) It has had three occurences of hard stumbling/power loss, lights up the check engine light. The drivability issues will continue until I turn the car off, and restart, at which time it drives normally again. When I pull the codes, it is giving misfire on cyl. 4, 5, 6. but not a "catalyst flow insufficient " code, which I would have expected. I am using a standard code scanner, as I have not yet bit the bullet on purchasing a STAR knockoff. I guess my question is for anyone who has had a cat fail, and checked the codes. Is the misfire on one bank telling me what I think it is, that the pass. side cat is plugging? I am taking her into the dealer for their diagnosis and have pre-ordered the cat (can't believe they didn't have it in stock, actually) but I would love some confirmation prior to a 1600.00 repair.

Anyone?

 

[faizano99]

Did you go with OEM cats or aftermarket?
Sorry if that sounds like a dumb question i just quickly read through it.

 

[BernardFarquart]

I haven't gone with either yet, the OE cats are looking like the only options, as all the aftermarket brands I have access to seem to only make the w210 cats, not the w211 cats. I was hoping for someone to pipe up with a similar problem, to validate my diagnosis based on the codes I am getting, but 274 views and one response from someone who didn't read my post are making me feel sad. I will be going to the dealer day after tomorrow. Hopefully I will get to talk to the tech at the dealer, and not just the service advisor.

 

[Simon_E]

If I'm not mistaken, cylinders 4, 5, and 6 are the driver's side cylinder bank, not the passenger side, which would point to the driver's side converter, obviously. You say you recognized the rattle as originating from the catalyst--how did you do that? You know that one way to find out is to take a rubber mallet and hit the catalysts on both sides from below (pre-cat close to the engine and main cat farther to the back, as well as the pipe in between)? If you hear it rattle inside, that gives you a strong indication that there are broken pieces flying around and potentially blocking the flow of exhaust gases.

My experience might vindicate your hypothesis. I have a 1999 E320--a different car, but with the same engine. At some point (178k miles), I noticed a clunky rattle at idle and when decelerating, which I traced to the passenger catalytic converter. (The driver side converter had been replaced by the previous owner not long ago). A few weeks later an independent Mercedes specialist confirmed that the catalyst was internally broken.

Incidentally, two weeks later on the highway I accelerated pretty strongly (although I didn't put the accelerator to the floor), which I don't do often, and at around 4000 rpm in third gear the Check Engine light came on and the engine started to run roughly. When I drove off the highway, it became even clearer (and worrisome). I stopped the car and read the code, which said misfire on cylinder 1 (which is on the passenger side). I turned the car off, cleared the codes, and when I turned it back on, the misfire was gone and didn't come back.

While I didn't try to provoke this again, two weeks later I did replace the catalytic converter, which I had resolved to do anyway because I knew for sure it was broken (moreover, the rear 02 sensor readings that I checked using my scanner--one you can hook up to your laptop--also indicated that the front converter was not operating properly any more).

With the new converter installed (and new front oxygen sensors, although that might have been just an act of preventative maintenance, because it's quite possible that the old ones were still working well), no misfire or other driveability issues have ever come back, even under hard acceleration (although, again, I don't do that often...).

 

[BernardFarquart]

That sounds very much like my experience. The catalyst makes a very specific rattle when the ceramic grid breaks down, I recognized the sound because I actually sell auto parts for a living, and have heard this sound before. I also have had lots of cars in various stages of their service life, so this is not my first failing cat, some of them have ended up drilled and poured out on the driveway, but this car will be getting a proper repair, as I hope to get a fair amount of use out of it still.

The sound was most noticeable when starting, so I actually spent a fair amount of time reaching up for the key with my head listening at the door sill, plus I had the services of one of my employees who stood around the car while I started, and restarted the car localizing the rattle.

I fully expect that there are sections that are shifting around, I believe this is what causes the hard miss, followed by the check engine light. I was pretty concerned about the cyl. numbers showing misfire, until this morning when i spoke to a service advisor at the dealership that I'll be going to, He told me that he has heard of this type of misdirection with cat failures in w211 cars, they will for some reason throw codes for the cylinders on the opposite side from the plug.

I discovered that clearing the codes that come up is not necessary to get the car to run smoothly, turning it off and back on seems to do that.

I am concerned that I may in fact need the drivers side instead of the passenger side, (or God forbid BOTH!) I am perplexed that this common part is not stocked at my local dealer, so I am hoping that it is only the passenger side, due to the three day wait, and my desire to drive to Portland on friday.

Once I have real answers, I will update this thread for posterity.

Thanks for adding your Data point.