Fuel System

The 7.3L Fuel system is pretty simple in it's stock form. It also can be a less than desirable system in it's stock form. For the most part it works as designed, but has so many options for upgrading that several modifications have been built for the fuel system.

7.3L Fuel System Diagram

Tank Components:

In the tank the fuel gets drawn through a pick-up commonly referred to as a "duckfoot". The fuel then gets drawn through a mixing chamber with two mesh screens. This mixing chamber is also the return path of fuel from the filter bowl on the engine. The return fuel is excess fuel that exits the fuel bowl through the fuel pressure regulator (FPR).

Fuel Tank Pickup Mixing Chamber

The fuel exits the tank through fuel lines with quick disconnects. These disconnects work pretty well when new, but can cause air to be introduced or the fuel system to loose it's suction holding ability. The disconnects require a simple tool to remove them. This tool is commonly available at almost all auto parts stores. The feed line is 3/8" and the return line is 5/16". Below is a diagram of how to remove the disconnect feature.

Fuel Line Disconnect Fittings (Click Picture For Larger View)

The fuel pump is an electric pump that draws the fuel from the tank via suction. Once the fuel enters the pump it is pressurized and sent to the fuel bowl through the fuel lines. The pressure is regulated at the fuel bowl through the Fuel Pressure Regulator. The unused and unfiltered fuel is routed back to the tank through 5/16" return lines.

The fuel pump has a slightly different quick disconnect on the aft side (suction side) of the pump. It has a plastic retainer that gets pulled out as the fuel line is pushed onto the pump, then you can pull the line aft.

Fuel Pump Disconnect Fitting (Click Picture for larger view)

Fuel Pump Mounted on L/H Frame Rail

Once the fuel exits the fuel pump it can be pressurized to over 100 psi. The fuel pump is a constant displacement pump. The pressure is regulated at the fuel bowl by the FPR.

The fuel bowl is located in the engine valley at the front. The fuel bowl contains a filter, fuel heater, check valve, fuel/water drain valve, water in fuel sensor, and the fuel pressure regulator.

The fuel comes into the fuel bowl through a 3/8" hardline directly from the pump. The fuel surrounds the filter from the outside and gets filtered by passing to the center through the filter element. Excess fuel pressure is vented back to the fuel tank through the fuel pressure regulator mounted on the top drivers side of the fuel bowl. Pressure is regulated to roughly 57 psi via the spring and poppet in the fuel bowl captured by the FPR housing. When the fuel pressure in the bowl builds it will unseat the poppet by overcoming spring pressure, this allows the fuel to return to the tank and the pressure in the fuel bowl stays constant, even under hard acceleration.

The filtered fuel flows through the check valve in the center of the fuel bowl and is then ported out the fuel bowl through two 1/8"-27 NPT ports on the passenger side of the fuel bowl. These ports pipe the fuel to each head via a 1/4" fuel tube to each head respectively. The fuel enters the head through a check valve and then fills the fuel rail in the head. The fuel rail is essentially a reservoir that feeds the injectors as they fire.

Fuel Bowl Exploded View