I would take him into the vet for a fecal test to rule out certain medical issues such as coccidia. Then if all medical issues have been ruled out, and you know it's just the odor, i highly recommend Arm & Hammer Multi Cats - it works wonders!!
He's eatin and drinkin loads and he did do a fur ball or sick thing the other day. He's active and coming back from outside a bit like he's been in a fight. No wounds tho. He's sleepin a bit more, not much...