Over time and miles, your car might start to slow down. It might not accelerate as quickly as it once did; the engine may not run as smoothly as you remember, or the fuel economy may dip—but ...

As you may know, diesel fuel can create gum and resin deposits in your fuel system and in your injectors. These finely engineered parts (they better be at $400 a pop) have only a small hole in the tip ...