The power output of a diesel engine is directly proportional to the quality and quantity of the air and fuel going into and out of the combustion chambers. So naturally, most aftermarket diesel performance parts are designed to add more air and fuel into the engine. Increasing the air moving through a diesel engine tends to result in a leaner air fuel mixture, so in order to build substantial power, extra diesel fuel has to be added.
The FASS fuel lift pump system requires its own fuel supply line from the fuel tank so Kelley Evans and Dallas Hunt removed the tank from the '08 Dodge Ram 3500. Obviously it is much easier to drop the tank when it is as close to empty as possible. Evans removed the electrical and fuel connections from the top of the tank and used a transmission jack to support the tank. With the tank supported from the underside, the tank cradles were removed.
The extra diesel fuel typically comes from an aftermarket programmer that commands the injectors to stay "On" longer and flow more fuel into the engine. Making the injectors flow more fuel certainly makes more power, but the fuel pressure coming from the injection pump may become unstable due to the fact that the factory fuel lift pump wasn't designed to support aftermarket horsepower levels.
HOW A DIESEL FUEL SYSTEM WORKS
Most diesel engines use a similar fuel system design regardless of the manufacturer. Typically, a fuel tank mounted under the vehicle holds 20-40 gallons of diesel fuel. A mechanical or electric lift pump is used to bring diesel fuel from the fuel tank to the injection pump that's mounted on the engine at 5-70 psi. An injection pump then increases the diesel fuel pressure up to somewhere between 5,000-30,000 psi so that when the diesel injectors are fired, the diesel fuel mixes with the air in the combustion chamber.
FACTORY FUEL SYSTEM LIMITATIONS
The factory fuel systems are generally capable of handling up to 100 hp over their factory engine ratings, but even at that level, the fuel supply delivered to the injection pump can fluctuate. The inconsistent fuel pressure can lead to losses in overall power, poor performance on the track, or even injection pump damage in extreme cases. For those of you considering adding larger injectors, twin injection pumps, and seeking four digit horsepower power levels, the factory lift pump just won't cut it.
With the cradles removed, Hunt and Evans lowered the tank from the truck so they could work on it. | 
Evans removed the stock fuel-sending unit and factory lift pump from the tank to make it easier to drill the hole for the new FASS fuel line pick-up. |  |