3126 Cats brown black smoke

Have 3126 cat mechanical engines. The port motor has 10lbs of fuel pressure at low idle seeing no air in clear tube at all rpms. Boost is 22lbs at cruise,brown,black smoke in water exhaust at power up and puffs black smoke at cruise.Turbo temp 850 degrees. The starboard motor fuel pressure is 24lbs at low idle and boost is 22lbs egt temp 900 degrees and no smoke. There is a visual tar around turbo inlet,not on the blades.Engine temps all checked out and within spec with a heat gun.Hull and wheels clean. Engines have just over 2000 hrs. Any ideas what could be possibly going on ? This issue recently started.Thanks.