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Discussion Starter #1
Does anyone know the name of the supplier of the SCR/DPF system on the 2011's? I have some technical questions I want to ask regarding sulfur tolerance and whether the catalyst is Cu/Zeolyte or FE/Zeolyte. It seems a good place to start with the manufacturer of the system.
 

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Even if you get the name(s), the company will have a Non-Disclosure Agreement (NDA) with GM and probably won't be able to talk to you. While SCR systems are generally more sulfur tolerant than, say, NOx adsorber systems, running much about the ULSD limit of 15ppm isn't a particularly good idea (either for the SCR catalyst or the catalyzed DPF).
 

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Discussion Starter #3
Hi kschmidt64.

You are correct about the generally higher sulfur tolerance of SCRs, at least according to ALL of the research I've done over the past 3 months. And we already know, after almost 4 years of real life experience, that the DOC/DPF arrangement on the 2007-2010s is very sulfur tolerant. Hundreds of GM pickups from those model years can be seen in Mexico every winter and, despite ongoing attempts to do so, I have never found a single documented case of a DPF problem resulting from the use of Mexican diesel (300 ppm sulfur). It therefore seems probable that the new 2011 system will be no more sensitive to sulfur than the system in the 2007 through 2010s.

However, just as I made it my hobby to thoroughly research the sulfur tolerance of the 2007-10 system, I would like to stay well informed regarding the new technology. The problem is, because Canada and the USA are now almost completely converted to ulsd for road fuel, the manufacturers don't seem to have put any/much effort into real life research of long term sulfur effects on the SCR/DPF combination.

There's every reason to believe that it is NOT a problem, especially for short term intermittent use, but if a study paper does exist, I'd like to see it, and if that paper has been presented at a conference then it won't be proprietary so there shouldn't be a problem accessing it.

Also, the GM system will have been registered with the EPA by the manufacturer, so the details about it's construction are somewhere in the public record. I'd like to know for sure that the SCR is in front of the DPF, and whether the SCR is Fe/Zeolite or Cu/Zeolite, or a combination. All of these things are important in assessing the likely sensitivity to sulfur.

If you know something that might be helpful, please do send me a private message.
 

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Hi Ted,

I doubt I'll know much that will be helpful to you. For the LML, you only have to stuck your head under one to see that the SCR is in front of the DPF. Ford does the same thing for the 6.7L pickup but reverses the order for the C/C units (different cert. cycle).

I wouldn't be so confident of the sulfur tolerance of the 07-10 systems for a couple reasons.

- Even if a fuel isn't ULSD, you don't have any way of knowing its real sulfur content without testing it. Plenty of stuff labeled LSD is still pretty low (certainly not 300-500 PPM). This can be true for parts of Mexico as well.
- I believe all of the Big 3 sell their pickups in Mexico, and they do so without a DPF.
- All the work currently going for using DPF's in a higher sulfur environment focuses on uncatalyzed DPF's. In the long run, higher sulfur fuel really is a problem for catalyzed DPF's, even if it doesn't show up after a few runs down to Mexico.
 

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Discussion Starter #5
Hi Again kschmidt64,

Regarding the SCR, it is built in to the same cyclindrical canister as the DPF on the 2011, so the combined unit is quite long, but when I looked at it at a car show in Kansas I couldn't see anything that would confirm that the SCR is in the front part, no way I could tell, although the GM rep said it was in the front part. There is still a DOC, but it is no longer in the pipe down from the engine, it is in the pipe under the floor, a few feet before the SCR/DPF, so it would be easy to assume that was the SCR. If you can tell me how to recognize that the DPF is in the front part, please do let me know what to look for.

Don't know if you've ever read my extensive posts on sulfur poisoning of the DPF, going right back to late 2006, but I posted links to several government and manufacturer tests which showed conclusively, absolutely NO doubts, that the DPF can be exposed to upwards of 300ppm for as much as 40,000 continuous miles and then recover completely once it goes back on ulsd. After around 40,000 miles of continuous use there is permanent sulfur poisoning which diminishes the efficiency. These test results, combined with 3 years of LOTS of owners taking their trucks to Mexico leaves me VERY confident that there is high sulfur tolerance, but time will tell whether the government and manufacturers' tests were accurate. I spoke with a Duramax engineer in early 2007 who told me that GM's "limited" tests using LSD were unable to produce a sulfur poisoning condition. He wouldn't tell me what "limited" meant.

At our last check of dealerships in Mexico, about 6 months ago, only Ford offered a diesel pickup, and they were almost impossible to get. Dodge offered gasoline only in a size equivalent to the 3500 but with a different name that I can't remember now. Only small gasoline GM trucks, no 2500s or 3500s.

Since my last post I've had interesting chats with folks from Corning and Meca who left me with the impression that there is every reason to believe that the 2011s will be just as sulfur tolerant as the 2007 through 2010s, because the SCR is less affected by sulfur than the other components already in service.
 
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