The original post was what is wrong with tier IV? I have said, 渡othing is wrong with the Tier IV emissions regulations, getting there with DPF and SCR/DEF is bad. Up until now I have been saying that you don't want DPF and SCR/DEF because it is riddle with issues. My next premise is "emission control components that are added to meet tier IV emissions that increase fuel usage are bad and do not really lower there over all emissions foot print. What I am saying is even when your, VW Diesel Passat, with DPF, is working correctly, because the DPF is causing an increase in fuel usage that is negating the emissions that the DPF is reducing. (I am picking the Passat because it was mentioned above and there is information available) Also, this concludes that we buy the soot being burned off has been turned into magical pixy dust and the scientist are always going to be right and that this isn't going to cause say cancer anytime soon. When fuel is refined it produces emissions. This is the reason for not approving the keystone XL pipe line, the oil from the tar sands is dirty and will therefore produce more emissions in the refining process. So, therefore the refining process must produce harmful emissions. So, if we use less fuel we produce less emissions. When the DPF delete kit is installed on the Passat there is roughly a 10% decrease. It's a stretch, but I do believe increase in fuel useage should be considered when, we say emissions are being reduced.