The following is part of a PM I sent a fellow user. It took me a long time, actually getting my hands dirty (god forbid), and talking with Dennis at ITP to figure out the stock system and how it all works.
I know some of you were born with this knowledge and may scoff at my elementary understanding of a stock PSD fuel system, but never the less, I needed to be educated.
I'm putting this out there so hopefully others who may not know will gain a better understanding of how the fuel system works and what ares of it need to be addressed.
I'll explain how the routing of the fuel goes from tank to bowl to heads to regulator/bowl, to return line back to tank, and the purpose/need for modifications to the fuel system.
1) Line comes from pickup in tank and runs to fuel pump
2) line leaves fuel pump and is fed into the bottom, DRIVER'S side of the fuel bowl You will see a hard line for this.
3) Fuel leaves the fuel bowl via 2 ports on the bottom passenger side of the fuel bowl. You will see 2 hard lines for his.
4) Fuel leaving those hard lines is fed to the FRONT of driver's side head and the REAR of the pass side head.
5) The Fuel then dead heads in the heads and there are check valves in each head at the feed locations. These check valves are thought to be there to minimize the affect of the harmonics created by the injectors firing asynchronously.
6) The fuel is regulated by the internal regulator in the bowl, whatever fuel is not needed is forced by the regulator and makes its way down the return line on the TOP-DRIVER'S SIDE of the fuel bowl
7) The return line from the regulator runs all the way back to the tank and is dumped in to a mixing valve, where it is mixed with new fuel coming from the tank. This preheats the fuel.
8) Areas that need addressed to eliminate (or at least drastically reduce) air intrusion, and fuel aeration are
>> a) Remove mixing valve in the tank, big source of aeration.
>> b)Remove quick disconnect fitting on the pickup going to pump. These quick disconnects seal fine under pressure, but under suction they leak air.
**Above A,B is commonly referred to as the "Hutch Mods" or also called "In Tank" or "Pre-Pump" mods.
Aside: you will also need to install some sort of pre pump filtration / water seperation as the mixing valve has 2 small filters which trap any particles that may make their way to the fuel pump and damage it.
>> c) Remove the "Dead Head" stock fuel system design by creating a flow through system which is externally regulated. This is accomplished by feeding the end of one head (doesn't matter which end) and allowing fuel to travel through the head and out the other side by means of connecting a return line from the head to an external regulator.
9) Deleting the stock fuel bowl is merely preference as it allows better access to the top of the engine, gives the engine bay a much cleaner, open look, and creates a wider choice of cheaper/better/more available fuel filter elements as opposed to the stock one.
The ideal setup IMO
will use a 10-100 non-restrictive filtration system pre pump and a finer, more efficient filtration system, such as a 2 micron element, post pump.
A heated pre pump element with good water seperating capabilities is also recommended, especially for those in colder climates.
While you have access to the tank during the pre pump stage of fuel system modifications, you can cut off the vent tube that runs along the factory filler nozzle to allow the tank to fill almost completely without activating the pressure-sensitive nozzle shutoff on diesel pumps. This is commonly called the "harpoon mod". Makes filling the tank completely a breeze.