a couple weeks ago i started noticing a slight fuel odor or smell in my C32 and also a strange metallic vibration noise coming from under the car in the middle area just below the front seats. car seems to be driving normal otherwise, no power loss or starting issues. no malfunction alerts etc. it has come up as the chicago weather has dropped into the 10-20 degree range.

i have 100k miles on it and for the life of me cant figure out exactly whats going on... is that noise a loose heat shield, catalytic converter problem causing noise and fuel smell, or fuel filter issue???? any one every have those symptoms?

car is out of warranty and i'm about to visit the MB dealer in westmont IL to have them check it out. help?

 

There's a metal bracket underneath the driver in that area that holds the exhaust. I had one of the bolts back out and my bracket was hanging by a thread. Check there for your loose sound.

 

Update - seems that the metallic rattling noise is coming from the area of the catalyic converters under the car. When in Park, if I press the gas pedal and the RPMs get to 1500 and higher the noise kicks in and continues until i take my foot off the gas pedal. I got down on the ground by the driver front door and listened for the noise under the car while a friend hit the gas and can definitely hear it in that area (catalyic converter).

Also now the power is now noticeably bad. At times while in drive, if i floor it the car takes 2-3 seconds before it starts to accelerate and the fuel smell becomes noticeably stronger.

Anyone every see this? I have No clue what is going....??? taking to a repair shop early next week

 

It sounds like this...this is not my C32, but found a youtube video of a C-class with similar issues of rattle noise coming from under the car and my noise is identical. I'm guessing its one of the Catalytic converters causing this.

 

probably a good bed that your right abou the CATs. You might want to consider replacing all 4 as old as your car is with 2 aftermarket highflow type. I'd avoid going to to the dealer as it'll cost some ridiculous amount of money for OEM. After market ie. magnaflo/ebay 100/200cell cats will be 1/2 the price, flow much better and will still pass emissions.

 

Both catalytic converters under the drivers seat are confirmed bad and have broken apart and are making the noise.

My indy repair shop said that if I go with mercedes OEM parts they only offer remanufactured cat's which are 850 for the right one and 1000 for the left one and thats just the parts!!!!

i am going to check out a local exhaust shop and ask if they can do something cheaper like a magnaflo with universal connector and weld that on...

any suggestions as to replacement cat's that are comparable to the OEM ones in terms of performance? I understand that any non-OEM cat will be a custom install and require cut/welding.

 

There's a ton of aftermarket cats out there that will perform better than OEM for 1/4 the price.


any semi competent exhaust guy can weld in aftermarket cats just as easily as OEM. The trick is finding a tech willing to mess with them not because of difficulty but because of liability.

 

UPDATE

I did get my car to MB dealer a couple weeks ago and they said no codes (was no CEL at the time) but they confirmed it was only the left secondary CAT was bad/rattling (not both like the indy shop thought.)

I just had a local Midas shop replace the damaged cat yesterday (i was pressed for time, normally wouldnt go with Midas) and it seemed to driving fine for about 30 minutes this morning while on the high way. But after a few 60 to 80 mph bursts the CEL came on and I started smelling fuel in the cabin when accelerating and the car just bogged down and wouldnt accelerate normally even when pushing the pedal all the way. After pulling over and shutting of the car for 5 minutes that seemed to temporarily fix the acceleration problem and the car was driveable but still not running right and the acceleration not where it should be. thats the first CEL ive had on the car in 8 years of owning it.

Could the bad performance and bogging down and also fuel smell be from the car running rich due to bad 02 sensors? would that throw a code having bad O2 sensors?

my c32 is at 100k miles so Ive read those should be replaced around 100k. I'm gonna get it back to Midas today since they had it yesterday and I paid $199 for a Catco converter and got charged $250 in labor and that didnt fix anything and now I have the CEL on (maybe my problem was taking it to Midas in the first place... shame on me

will update again as i find out more on this one...

 

Your car has four cats. Two primary and two secondary. It’s a very good idea to replace them in pairs. If one primary dies, replace both primaries. Ditto for the rears. Also, despite the fact that your cat came apart, the original equipment part was what is considered a high flow cat. Based on your description, it sounds like you now have three high flow OE cats and one Catco universal fit converter. Personally I’d cut my losses, go to a independent muffler shop, have them remove the new Catco, and install a pair of metal substrate cats.

Why? Your new cat probably doesn’t flow as well as the other three and under wide open throttle, one bank of cylinders may not flow very well. That may be triggering the CE. Lastly, *I think* it would be a very bad idea to allow Midas to install a second "secondary cat" to even out the flow - which is what they may recommend.

 

MarcusF - great feedback, really appreciate it. What you described makes sense because I was driving on the damaged MB original secondary cat for a month and it never triggered a CEL and did pass emissions. This mix of the Catco and the MB original high flow for the other secondary was probably a bad idea.

Is there a specific manufacturer for metal substrate cats that you know of and can be used in Mercedes AMG's? Magnaflows is one i've heard mentioned.

Another other route I'm considering is to delete both secondary cat's (as many on MBworld have described doing, mostly for sound) and run stainless steel pipes in place of the secondary cats (will keep the resonator). I assume that is the cheaper route since the cats will be more expensive than SS pipes, but not sure if its necessarily better (?) or will get the car running normal and clear the CEL.

 

Random Technology (7000 series) and Magnaflow are both good manufacturers. Some prefer deleting the secondaries and going with SS, others prefer a second set of cats. Those who prefer a second set of cats can point to a theoretical improvement in performance.

How can additional cats make more HP?

The hotter the exhaust gases, the faster they will flow. Since using metal substrate converters (in this case as secondaries) doesn’t impede flow and they reheat the exhaust, the exhaust should flow faster. Faster flowing exhaust always translates to a more efficient engine, which should produce more power. At least that’s what every cat manufacturer I’ve ever interviewed has claimed. Although manufacturers are not exactly a neutral party, their logic makes sense.

 

Do real race cars (NASCAR, F1 or Pro Drag racer) have cats?

 

The question is moot. Now you’ll have to excuse me while I get off my heels and on my wheels.

And yes, I do get the car.

 

Not sure about your usage of "The question is moot" since it has two different meanings.
Your conclusion about running without secondary cats is incorrect. You gain power after removing cats. Granted, on a C32, if you remove the secondary cats one may gain 2 HP and 2 LB of torque which is not much and is not worth breaking the law over. Unless the repair of the cats will coast you $500+. Then everyone will make their own conclusion.

 

UPDATE - i checked codes with a nice little Actron tool from autozone and its showing a code "P0123 Throttle / Pedal Position Sensor A Circuit High Input" as CONFIRMED. Theres another code PENDING described as "P0451 Evaporative Emission System Pressure Sensor Switch Range/Performace".

my O2 sensors showed these values - not sure what the right O2 sensor ranges are which i'm researching now:

O2S11 (V) = 0.465
O2S12 (V) = 0.470
O2S21 (V) = 0.470
O2S22 (V) = 0.465

the cat that i just replaced was the drivers/left secondary..so maybe the O2 sensors are ok and the problem is the code P0123 Throttle / pedal in addition to the 2 different secondary cats i have now (ie: the Midas Catco one thats non-high flow and original MB?

 

It sounds like you’re unfamiliar with the SNL skit, “the question is moot”. I suppose that’s understandable. The skit is from the 1980’s. The lines “Now you’ll have to excuse me while I get off my heels and on my wheels” as well as “yes, I do get the car” also come from the same skit. Basically, it was an acknowledgement that I recognized your post as a loaded question. For me, the question is moot because it's a lead in to argue about meaningless drivel.

Before stating my conclusion is wrong, you may want to make sure I actually make a conclusion. Perhaps you just didn’t read my post clearly. In rereading it, you can plainly see I didn’t state my personal opinion on the performance improvement of running with or without secondary cats. I stated the “theoretical improvement” claimed by catalytic converter manufacturers and then stated those same manufacturers are biased. As for my personal conclusions, I’ve written three published magazine articles specifically about cats, and at least two others on exhaust flow (both boosted and NA), so I am somewhat familiar with the subject. Here, the only question I see is whether the low pressure zone introduced by the new secondary cats results in a negative pressure wave that is (measurably) detrimental to performance. How can one tell if the wave timing is bad? Numerous dyno before and after runs. Although, having seen the stock C32 exhaust manifold, a possible negative pressure wave may not be the primary concern.

Other than the wave, I can’t see the performance downside. Maybe weight, but I doubt that has a measurable impact. I do know 7000 series Random Technology cats are not the exhaust bottleneck on an otherwise stock C32. How did I reach that conclusion? If we assume a certain 3.2 liter engine is running 14.5 PSI @ 6000 RPM and is operating at 100% VE, the engine flow is 666.341 CFM. Each secondary cat only has to flow half of that. Can the cats I recommended flow 333 CFM? Random Tech 7000 series cats flow 500+ CFM each at 20.4” H2O. Since those cats outflow the primaries, the muffler, and the engine itself, there's a very high likelihood that they're not in the way.

 

Clear all CELs and do a "sneaky ECU rest" to see if that clears the P0123. Use search if you don't know what it is.
The P0451 is can be related to a loose gas cap. It can also be a disconnected breather hose on the driver side air box. And numerous other reasons.
Regarding the cats, if you live in a state where there is no visual inspection, replace both secondary cats with a SS pipe and be done with it. Otherwise get two of the same kind of cats (what Marcus recommended). It is not a good thing to mix different type of cats and therefore the results may be unpredictable.

You are right. I was unfamiliar with this particular SNL skit from the 80s with Jesse Jackson. Watched it on youtube and it is funny, especially coming from Jesse. I read your post clearly. When you said "Although manufacturers are not exactly a neutral party, their logic makes sense" I took it as your conclusion. I'm glad it is not and I agree with you that the question is moot.

 

That skit is hysterical. I remember a time in the 80's when people started using that in meetings at my job. Someone would to speak, only to be interrupted with “The question is moot!!!!”. IIRC, management's lack of enthusiasm resulted in that expression being banished.

For those who are completely lost, here’s the skit. And Jvakos gets the car! Since he started the thread, he’s the OP and if anyone has any questions, save your breath. Those are probably moot too.

 

Lenin - much appreciated. Will clear the P0123 "pending" code using that Actron tool i have and rip out both secondary cats and do straight pipes and FINALLY be DONE with this cat problem!!!! Will update as I get this to that conclusion...

And also thanks to you and MarcusF for your wit and humor...i forgotten about that SNL skit (Moot, I get the car!) so its even funnier having watched it now and re-reading your responses!! ha.