My truck didnot pass smog test for the second time.

Agreed--black smoke (not bluish-gray) is a sign of running extremely rich.-to much fuel OR not enough air.It needs proper diagnosis. Check your local laws- many states with emissions testing have certain criteria for shops to pass and they can be 'certified' in emissions REPAIR. Emissions and drivability issues are two different things. You don't see to many dragsters getting passed an emissions test , but when they're doing a 1/4 mile in 5 seconds----who cares??(besides the EPA)...............GREG is a 'GOLD SHEILD' station what they call an emissions repair station in CA.?