I have a 1999 Isuzu NPR Turbo diesel 4.8 and it sounds like an exhaust issue but only when I hit the accelerator. I hear it is the loudest (and see gray smoke) at the front of the valve cover and maybe slightly below. Also, there is an excessive amount of black soot building up in that area on the engine and on the underside of my tilt cab. People drive by me and complain that my truck is blowing too much smoke. Is this something more than an exhaust issue? Is it related to my EGR? Also, my oil was blacker than black when I changed it yesterday. Please any help?!?!?!