Where is the catalytic converter located on a 93 300SE W140? When I look at the exhaust coming from the manifold, I see two "bumps" on the downtubes that combine into one. From that point, someone has installed a section of pipe, thus removing the bung for the O2 sensor. What I can't figure out is if this is where the catalytic converter was located, or if the two "bumps" in the downtubes are the converters (I don't believe they are, but I want to make certain). I believe the O2 sensor goes before the catalytic converter, so I believe someone has removed the converter and the bung for the O2 sensor.

I plan to have the O2 sensor replaced because the idle is very poor and the car is running very rich. The question is, should I have a catalytic converter installed at this section (downstream from the O2) as well, or just have the bung installed for the O2 sensor and call it a day?

Do an image search on M104, W140, catalytic converter. Also do one on M104, W140, O2 sensor.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

I did that, I didn’t find a real definitive picture until I found one that showed the heat shield above the catalytic converter. I noticed there is a heat shield above the straight pipe that someone put on, so I feel confident that is where the converter should be. I will check with my exhaust shop to see what they can offer as far as a replacement converter that has a bung for the O2 sensor before the converter. I don’t know why people remove things from these cars, especially an O2 sensor, knowing that they won’t run right afterwards. You can get by with that on some cars, but not a Mercedes.