lots of smoke... not good

lately i'm geting some black smoke when i push the pedal, except the usual gear change smoke wich is not unusual for diesels. had my pump tested(was fine), injectors cleaned etc. searched and searched again for the 02 sensor and can't seam to find it. any body know if diesels have one? maybe some links or something? otherwise engine runs great( except allmost dead turbo).
i'm thinking it's somehow programmed to put in more fuel over the rpm the turbo is supposed to kick in and pump air in it... any ideas?

I got interested in diesels just long enough to realize that I'm not interested in diesels. But one thing came up a lot: they like to be driven for long distances at high speed every now and then, clears out a lot of built-up carbon, frees up the rings, lots of good stuff. A nice trip on the freeway, at least 50 miles, might do some good.