The fuel system business is booming. Aftermarket pumps, regulators, lines, fittings, tanks, injectors, fuel rails—even entire how-to books—revolve around the task of delivering more fuel to an engine.

If you browse forums often, chances are you've come across some heated discussions around the CP4 fuel pump. The CP4, short for "Common Rail Pump 4," is a high-pressure fuel injection pump that made ...