What is the best/perferred way to check the intercooler and intake system for a small leak and is there a good way to tell if the fuel return lines are leaking air? I've posted before that I'm getting poor fuel economy and have verified that I'm only getting about 12 mpg(used to get 17+). My daughter was following me yesterday and said that every time I was idling at a stoplight, there was visible smoke and the smell of diesel from the truck. I've replaced the fuel filter, drained the water fuel separator, had the timing checked (+15 degrees) and done a visual inspection of the hoses coupling to the intercooler. Problem is if I have a small hole in the hoses or the intercooler, I'm not sure I would have seen it.