i completed an lpg cert 2 course, and i dont know if there is any truth in this, but we got told (by our instructor) that 90% of petrol vehichles with cat convertors are contaminated within about 100 km of of purchasing the vehichle. unless you get the catylic convertor to the correct temp, which would require a minimum of at least 15-20 minutes to actually heat the sucker up to burn co2's and the nox's and all the yukkies. all this has to be above 80km's of constant driving. the cars that are stuck in traffic are not doing their jobs either. you need the heat from the exiting exhaust gasses to push and flow through the cat convertor for all stuff in the cat to do what it was meant to do. now if there is any truth in this, were being lied to by poeple who have a higher pay grade than average joe. i know that we have pre heating o2 sensors and the what not's, but if theyre not doing jack, why are they fitted. that would mean all car manufacturers accross the globe are still poisoning the world. maybe it's not true, i dont know but im just relaying what i was told.