RE: diesels and o2 sensors
As Chief Engineer Montgomery Scott once said, "the more complicated you make the plumbing, the easier it is to stop up the drain". And that certainly seems to be the intent of the Feds and CARB when it comes to diesels.
After retiring from the Navy in '97, I went to work at the Freightliner plant in Cleveland NC, and spent a good bit of that time as either an assembler or inspector on the engine assembly line. In that time I've seen 3 different increments of emissions controls implemented. The last round in '07 was by far the worst.
As far as O2 sensors, you're pretty safe in assuming that anything built before '07 does not have an O2 sensor in the exhaust. Primary change up until that point was adding increasing levels of exhaust gas recirc - EGR.
Besides being pretty bloody stupid from an engine life standpoint - sucking soot and other junk into the intake, combining it with oil vapor from the CCV to form nice gooey deposits that gradually choke off the intake manifold - the intent was to reduce combustion tenps in the cylinders - also reducing efficiency and fuel economy - to reduce production of NOX.
Added change in '07 was to add particulate filters in the exhaust to capture the added soot resulting from use of EGR. And to burn off the soot that accumulates in these filters, they had to add an extra injector in the exhaust or dump extra fuel thru the engine to jack up exhaust temps to regenerate these filters. So now you're burning extra fuel just to clean out that bloody filter - which is resulting in a 25 to 50 percent hit on fuel economy. On vehicles where they simply dumped extra fuel into the engine, and got the programming wrong, they jacked exhaust temps up to the point they were actually melting turbos. And if you don't allow the ECM the chance to regenerate the filter (ie, due to your driving routine), the ECM will put the truck into limp mode and make it undriveable until you allow it to do it's thing and regenerate that blasted filter - 45 minutes to an hour until you can drive the vehicle.
Here's the catch - all the engine manufaturer reps I've spoken with say that if the EPA would allow them to tune the engine for max efficiency and use aftertreatment in the exhaust for NOX - no blasted EGR - soot production would go to virtually zero, fuel economy would take a drastic jump upwards, and other pollutants would see a drastic reduction as well. But the suits at the EPA have decided that they know more about diesels than the people that actually build them.
On the subject of the EPA and biodiesel - the EPA doesn't like biod because they say it drastically raises NOX production - based on a single test of 3 diffeent engines, of which they picked the worst case scenario. But I've read several test reports conducted by the military - accessible online if you do a Google search - on virtually every type of diesel engine they use - that showed no difference in NOX production between ULSD and biodiesel.
Main focus that seems to be driving the EPA - hybrids are politically correct, clean, and green, while diesels are dirty soot-belching monsters that they would prefer to do away with entirely. I've spoken with a gent at one TDR truck meet, who helped (or I should say tried to help) the EPA draft their diesel emissions regs. No testing, no reasearch, nada - he said they were simply sat down in a room with internet access and told to write regulations for diesel emissions from what they could Google on the web. And speaking with EPA personnel while doing this, he said the attitude of a large part of them was that they didn't give one whit what effect these emissions requirements would have - the more restrictive the better, and if it had the effect of eliminating diesel useage in this country, so much the better - they wanted to do social engineering and kill off diesels entirely, and have everyone driving hybrids.
'87 MB 300D Turbodiesel
'05 Jeep Liberty CRD (Common Rail Diesel)