Are my Cats going Bad?
Thread Starter
Junior Member
Joined: Feb 2011
Posts: 21
Likes: 0
From: San Gabriel, CA
96' E320 W210
Are my Cats going Bad?
I wanted to know if their was an easy way to determine if my cats were going bad? I can hear a slight rattle, but not unless I'm really listening. Also, I suspect my Exhaust Gas Temp is higher then it should be. They are original and I'm sure well over due for replacement, but they're not cheap. So I'd like to know for sure if they are in fact bad. I replaced the water pump just yesterday, so it'll have to wait until next pay check, but whats a good source for new Cats? Stock, or High Flow? 
MBWorld Fanatic!
Joined: Oct 2007
Posts: 1,564
Likes: 19
From: SoCal
98 Brilliant Silver E320 Wagon
Quite a few things can cause a rattle.
One way to tell is get under the car with a rubber mallet and hit them. As you know damage is caused by over-heating which is usually caused by a faulty MAF and/or O2 sensor. So if you need cats chances are you need those if they haven't been replaced recently.
Most muffler shops can weld in a universal replacement. Some are pretty reasonable compared to the factory ones. Be sure to get CAB approved ones for California to keep the smog boys happy.
One way to tell is get under the car with a rubber mallet and hit them. As you know damage is caused by over-heating which is usually caused by a faulty MAF and/or O2 sensor. So if you need cats chances are you need those if they haven't been replaced recently.
Most muffler shops can weld in a universal replacement. Some are pretty reasonable compared to the factory ones. Be sure to get CAB approved ones for California to keep the smog boys happy.
MBWorld Fanatic!
Joined: Feb 2008
Posts: 1,803
Likes: 12
From: Charleston, SC
GL450
You can hear if they're bad by either tapping them with something (wrench or rubber mallet) or park next to a wall (so you can hear the noise bounce off the wall), rev the engine, and then let off the gas quickly. You should hear a rattle as the motor slows back down, and you'll hear it bouncing off the wall.
You want aftermarket. The stock ones are very expensive. You can find them online, or most muffler shops will have some generics in stock to weld in.
You want aftermarket. The stock ones are very expensive. You can find them online, or most muffler shops will have some generics in stock to weld in.
Senior Member
Joined: Nov 2004
Posts: 391
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From: San Jose, CA
2000 E430 Sport
I cut off my primaries a month ago and thought I fixed the rattle that I had. Just took the car to the muffler shop on Friday and found out my right hand side secondary cat is bad. I found a lady on EBAY to sell Magnaflow Hi Flow Universal Converter 53005, for $47 each & free shipping.
http://cgi.ebay.com/ebaymotors/ws/eB...TQ:MOTORS:1123
http://cgi.ebay.com/ebaymotors/ws/eB...TQ:MOTORS:1123
