3-way Catalytic Converter

A couple years ago, I invested a LOT of money in a custom 3" stainless steel exhaust system for my 2001 Audi A4 1.8T. A large chunk of that money was spent on a 3" downpipe with a high flow cat.

If at all possible, I'd like to retain that exhaust system. It's treated me very well over the years, it looks fantastic and it sounds awesome... and as I said, it cost a LOT of money.

But obviously it's got a 3-way cat since it was designed for a gas engine. How will a 3-way cat hold up to a modern diesel engine and ultra low sulfur diesel?

edit: to clarify, in Vermont, there's an annual safety and emissions inspection. If an engine had a cat from the factory, then it must be present to pass inspection. I see a cat on the Passat donor vehicle. Vermont does not actually measure emissions at the tailpipe, so its efficiency doesn't really concern me in that regard. But it would be nice to be compliant in spirit without causing mechanical issues.

curious about this as well ... three way cats are much more available and i'm considering adding one to my truck swap

The diesel will plug them up in a hurry as I understand it...

-J

compu_85 said:

The diesel will plug them up in a hurry as I understand it...

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I didn't think it had anything to do with "plugging" but rather the rapid exhaustion of the rhodium in the converter due to the fact that diesels don't typically run rich at all. If that's the case, it's not a big deal because the rhodium is only used for reducing NOx, and 2-way diesel converters don't deal with NOx at all.

I'm mostly wondering if the other 2 processes of the converter will still function as expected.

Diesel soot can plug up a converter I put a universal three way on our diesel forklift and 3 months later it was plugged nearly solid. Larger cells will help though.

Scott_DeWitt said:

Diesel soot can plug up a converter I put a universal three way on our diesel forklift and 3 months later it was plugged nearly solid. Larger cells will help though.

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Scott, sounds like you need a diesel particle filter in front of the convertor!
Then you need to "lite" off the DPF a couple of times a week also!!

Easy way to solve this...if your state doesn't measure for emissions at the tail pull the cat, get a hammer and a stick of re-bar and knock out all the BS inners and BAM! High flow cat in place with no plugging but still serves its purpose of being there..

89vr6 said:

Easy way to solve this...if your state doesn't measure for emissions at the tail pull the cat, get a hammer and a stick of re-bar and knock out all the BS inners and BAM! High flow cat in place with no plugging but still serves its purpose of being there..

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I think you missed this part of my OP:

GoremanX said:

But it would be nice to be compliant in spirit without causing mechanical issues.

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Besides, there's more to it than just being compliant with the law. I've smelled diesel exhaust with and without a cat, and the presence of a cat helps to remove a lot of the diesel smell that many people find offensive.

In any case, based on the feedback I've gotten here, I think I've decided to just have my downpipe modified with a new high flow diesel cat. Shouldn't be too expensive.