Thanks everyone for these great comments!!

I bought the 400Es exhaust system from Timevalve and they were my 2nd call on this project. They no longer resell cats and referred me off to another vendor. The suggested vendor doesn’t sell to end users.

The shop said the cats are plugged. I should have asked how they determine this but didn’t think to do so. The shop has always been credible. I also remember another member’s tale of agony related to troubleshooting what turned out to be a plugged cat. Seems replacing it is an efficient means to NOT have to troubleshoot a bunch of other stuff.

In the really good article Ikchris referenced below, there is a nice detailed overview of cats. https://mbwholesaleparts.com/StarTu...atConvMar05.pdf One of the areas covered is how to test a cat for different kinds of failures.

In another part of the article they claim that one of the chief differences between after market and OEM cats is the volume of air flow. And the relative efficiency of the cat. They claim that the OEM cat has much higher values for both and that these values permit optimal performance for a longer period than does after market. Based on this my question is how do you find the specs for cats?

There is small cross section of cats for the 400E available on the web. Not every site has one for this model (I looked at all referenced above).

Here are some examples of what I found

http://www.catalyticonverters.com/MBE420MB22729294.html

not sure that this is correct but it’s the right engine and year. They state $494.14

These guys sell at 557.51

http://www.***************/cscmmp/mercedes/400e/catalytic_converter.html

These guys sell a brand called DEC at 525.95

http://www.***********************/mercedes~400e~catalytic_converter~dec~apwcbmmp~apwmb22726178ea3.html?apwcid=L1092232221W411a241dbe70 a&apwkwd=DEC+Catalytic+Converter+Mercedes+400E

These folks sell a brand called Miller for $655.72

http://www.***********************/mercedes_benz~400e~catalytic_converter~apwrmmp~apwh3000-84397b988aa.html?apwcid=L1092232221W411a241dbe70a&apwkwd=Mercedes+Benz+400E+Catalytic+Converter

Fastlane sells the Miller brand as well.

Is there a different colleciton of parts that come with these? As example are heat shields included with the cat? Are flanges and rings included?

Lastly, I'm intrigued the dbenz1’s comment to buy a universal cat. How does one adapt this to the vehicle? Are there specs for the size and form factor of cats? Or is the part standard enough so that it is fitted by displacement, or perhaps something similar?

__________________
...Tracy

'00 ML320 "Casper"
'92 400E "Stella"