2 ways 3 ways cat converters?

[haybayian]

I have a pair of  3" 3 way cat converters and hope to be able to use them.   Whereas 2 way cats are the norm for VW diesels (I think) is there a reason why 3 way cats would not do the job (i.e. satisfy emissions requirements). Does anyone know?

Haybayian.

[bigblockchev]

I believe that diesel cats are a completely different animal than a gas cat. The diesel system works with the ECU which injects more fuel periodicly to burn off the soot captured by the catalyst matrix inside. Mercedes calls them a "trap oxidizer" , only put them on California cars and issued a recall to remove them all and replace with a piece of straight pipe. That said none of this may be relavent to your car. If these are 3" diesel 3 way cats they may work, if they are 3 way gas cats I'm thinking not. Cheers Dan

[haybayian]

I believe that diesel cats are a completely different animal than a gas cat. The diesel system works with the ECU which injects more fuel periodicly to burn off the soot captured by the catalyst matrix inside. Mercedes calls them a "trap oxidizer" , only put them on California cars and issued a recall to remove them all and replace with a piece of straight pipe. That said none of this may be relavent to your car. If these are 3" diesel 3 way cats they may work, if they are 3 way gas cats I'm thinking not. Cheers Dan

I am affraid you must be right. Nowhere did I read anything that would suggest that gas and diesel cats are interchangeable.
Thanks for your input.
Haybayian

[the caveman]

There are diesel cats that do not need any processing or control with an ecu like a gas car which has to have proper fuel management so the converter can load and unload oxygen. after the first TDI's came out here in the passats, vw stopped with the fuel injection into the cat. Look at the later ones, there is no sensors, feed pipes, etc on the cat. it is benign- just functions to clean whatever comes out of the exhaust. I'm going to install one instead of a muffler when i turbo my truck. If you had a TDI with a clean cat, running on WVO it would be more economical and almost as clean as a Prius

[jtanguay]

I believe that diesel cats are a completely different animal than a gas cat. The diesel system works with the ECU which injects more fuel periodicly to burn off the soot captured by the catalyst matrix inside. Mercedes calls them a "trap oxidizer" , only put them on California cars and issued a recall to remove them all and replace with a piece of straight pipe. That said none of this may be relavent to your car. If these are 3" diesel 3 way cats they may work, if they are 3 way gas cats I'm thinking not. Cheers Dan

that sounds like the new diesel particulate filter.  it's only on the new common rail diesel engines.  they have an injector upstream of the particulate filter that injects fuel when its too clogged up to burn the soot particles completely.  hurts mileage a little bit, but works great (so far... check youtube for some funny video's)

older diesel cats work like the gasoline cats, except they have to be built differently because gasoline engines have a lot of waste heat, so its easy to bring the catalyst (such as platinum) up to like 500-600C to burn the unburnt carbon.  i'm not sure, but i would imagine that a diesel car with a CAT driven to and from work 5km would have its cat plugged up real nice... good highway driving for at least 30 minutes should help clear it out.  i just can't see it getting hot enough to burn the unburnt carbon in city/town driving...

[the caveman]

i'll plead right now that my memory is shot and don't have any of my lit here, but they do something similar to gas cats in respect to changing the chemical composition of the exhaust. maybe carbon monoxide to carbon dioxide,but i'm probably wrong, just an example.
 the older ones don't work as a particulate filter, that's only the new  diesels coming out although i believe some large trucks have had them for a while. i'm sure they get plugged with carbon after a while but if the engine never had an oiling or overrich condition it should last for at least 200,000 kms. this all is all info taken from vw and really relates to TDI's. vw were supposed to start using them as early as 94 or 95, but now i don't remember any ecodiesels or anything with a cat until the first TDI's showed up in 96 or 97.

[bigblockchev]

The soot trap/catalytc converters that I am referring to were tried on the 80's& 90's vintage mercedes but found to have all of the detriments that JT has suggested. VW tried them on at least the early AAZ cars My 93 Passat  ECO had one for instance. I am not aware that there is a diesel cat that you can install on any diesel car and have it function properly. I suggest that for this to work the cat has to be engineered as part of the fuel  injection system to clean up the emissions. I am dubious that the average enthusiast has the resources to even test the effectiveness of the cat.  If the engine that you are using came with a specific Cat and you are retaining all of the sensor elements and ECU then I suspect that it will work fine. It seems to me that most of the members on this board are into cranking up the fuel to get more power from their engines. I very much doubt that a catalytic converter will function as specified in light of these changes. The amount of black and white smoke coming out of the back of the various cars in videos on this board  tells me that. In older IDI VWs I do not think that it is likely that a cat will do much, in the TDI versions I expect that they might be effective. Cheers Dan

[the caveman]

no you are right in some respects. like i said i'm pretty sure the only ones i saw were on tdi's, therefore i guess to work properly they need the close fuel management. and i'm sure having that much soot and whatever will cause a cat to either function poorly or not all. however that's not to say it couldn't work and i'm going to try anyways. haven't got the money for a 4 or 5 or 6 gas anyalizer, and i wish i woulda checked my tdi before and after i blew the turbo [i'm sure damaging the cat],but next time i can,i will.maybe i'll be able to post some results.

[the caveman]

so the vw diesel TDI converter is made with aluminum oxide as opposed to platinum etc. 80% of the hydrocarbons are converted into water vapor and carbon dioxide. There isn't any NOx reduction, that's what the EGR was for.the reason they used to feed fuel into the cat was to lower the NOx by decreasing the oxygen in the exhaust. easier to use an EGR.
So all this to say that an aluminum oxide cat will work on any diesel.