Rich condition(black smoke) -at about 1/4 throttle?

this one a real hair puller.super rich at about 1/4 throttle computer is working -controls injector pulse width.had a broken ect already fixed ,played with maf cannot get voltage to 2.0 volts at idle-no drop outs or glitches-swaped with 2 other unit no difference,tps good,o2 sensor reads but not in closed loop.any ideas.truck was running fine happened all of a sudden- thanks ahead of time-ps fuel regulator not leaking