2002 ranger 3.0 v6 fuel consumption problem

I have recently bought a 2002 ford ranger 4x4 with a 3.o LTR v-6 engine
the question I have is what could cause terrible fuel milage in this truck ??????????? its getting about 150 to 175 kms per tank of fuel!!!
and no its not leaking out or being siphoned ! truck has 105,000 kms, there is no eng light on or codes as it has been scanned for codes .
I 'm thinking EGR problem like plugged passage or something.idle is about 900 rpm when warmed up ,also down stream O2 reading rich all the time and upstream O2's switching all the time (working) other thought are fuel pressure regulator ,I am trying to find an awnser to this as it is very costly to feed !!!!! any help appreiciated.

check your electricals for the injector harness, i dont know if thats the problem being its an 02, but you never know.