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1990 560 SEC(gone but not forgoten) 1988 560SL 1998 E320 4matic wagon
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Discussion Starter #1
After a bunch of trouble shooting found the pass side cat clogged on our 98 e320 4 mat wagon. Bashed the guts of the cat out and runs ok but a little rough. looking for recomendations for the best deal on a replacement. lowest ive found was about $450 any recomendations???
 

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1999 E55, 2001 E320, 1990 560 SEC, 2004 ML350, 2001 ML55, 1995 S500, 1998 SL500, 2010 E550 Sport zoo
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7,035 Posts
If front cat - and if non-California least expensive replacement overall is to find a reputable muffler shop weld in a universal front replacement.

If rear cat - those can be cut out, emptied, and if internal screens intact re-installed.
 

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1990 560 SEC(gone but not forgoten) 1988 560SL 1998 E320 4matic wagon
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258 Posts
Discussion Starter #4
front cat was completly gone. Rear cat was plugged with crap from front. I took a piece of 3/4 pipe and busted out the rear and dumped the whole thing out and reinstalled it.I took off the drivers side cats and they look good with no rattles but as quickly as this happened I'm kind of leary about not doing both. I think the back pressure inballance is probably causing the roughness. By the time I buy 2 cats and have them welded in I'm almost up to the cost of a complete unit.
 

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Outstanding Contributor W221 Moderator
2010 E350 P1/P2, 2008 S550 Designo, 2002 ML320
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any thoughts???
I seem to remember that some folks have had the rears replaced with straight pipe, however the fronts will likely cause problems if there is no catalyst. The O2 sensors are before and after the front cats on each side, which will eventually lead to the fuel management system being unable to correct the air/fuel ratio. I bed you are correct about back-pressure as well. I think if both my fronts and rears were shot, I'd just replace them with the best aftermarket stuff I could find.
 

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'82 300td (sold)
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304 Posts
I doubt you'll have much exhaust imbalance -- catalytic converters really don't produce much back pressure if they're not plugged up. The problem with OBDII cars is that they do measure emissions at two points in the exhaust flow, and if the readings aren't on spec the computer will probably throw a code.

Unfortunately, aftermarket converters have a poor reputation for performance and longevity. And you may still get error codes with aftermarket converters because their performance doesn't match the factory spec.

At this point, I'd run the car as is and see what happens. I don't think you'll hurt anything but you may get a check engine light because of OBDII -- and you may not pass a smog test. You'll likely get some resonance from the now-empty chamber the exhaust is pumping into.

Meantime, I'd keep an eye out for someone parting out a low-mileage W210 E20 and see if you can get a working set of factory converters that fit your car. It's not exactly legal and you'll still pay some coin because of the factory units' scrap value, but you'll have a quality system that you won't be cursing in a year.

BTW, I just went through this with an E34 BMW. I ran the car for several months with one hollowed-out cat, no problems. Engine balance was much better than when one was plugged up, I can tell you that!
 

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1990 560 SEC(gone but not forgoten) 1988 560SL 1998 E320 4matic wagon
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258 Posts
Discussion Starter #9
Yeah the sound is bad for sure. I did take both sides off and the drivers side looks good. But can you tell if its going to fail??? Not ratteling or anything. I'm tempted to do just the pass side and see how it is.
 

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'82 300td (sold)
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Yeah the sound is bad for sure. I did take both sides off and the drivers side looks good. But can you tell if its going to fail??? Not ratteling or anything. I'm tempted to do just the pass side and see how it is.
I think you're on the right track. A shop with an exhaust back pressure gauge should be able to get a reading on how freely the pass side flows. The cats aren't like brakes or suspension, you don't have to replace both sides at the same time. Just fix what doesn't work.
 
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