Hi brian
I bought a 2002 xt 2 years ago from a local nissan dealer,when i collected the car i noticed on the way home that it was badly smoking i took it back to the dealer they tried injector cleaner and told me to drive 500mls and see how it was,this made no difference,we also had black soot all up the front of the van,i then took it back to them and they replaced all the filters(it was ment to have been serviced before i collected it)and told me to try again,this also made no difference,so they fitted new injectors it was better but not acceptable,it was embarrasing when i accelarated hard and the car behind disapeared in a cloud of smoke.
I found some info on the x trial forum about the fuel ecu on some early models being programed wrong and causing over fueling,this is a known fault on early x trails but nissan won,t repair it unless forced to.
Armed with this info the dealer agreed to fit me a new one and the fault went away.
It is now fine and the van is cleaner,i am a service engineer and drive alot for a living,i see lots of early xt with the same fault,its worth getting it sorted because it can cause turbo/intercooler problems hope this helps,
Andrew