So, after months of trying to fix my truck's (Mack) rough idle / miss, and watching my fuel pressure drop a few PSI, I'm finally installing a new fuel pump. In the tank. Mack is a 2000 F450 C&C with a 40 gallon steel tank.

The reasoning behind putting the pump in the tank is to eliminate any possibility of air getting into the fuel system. The originator of this mod is kwikkordead, who has been a great help to me. Thanks Dan!

So here's my version:



First, I bought a new Bosch pump (69430) from Rock Auto. Then I removed the sending unit from the tank and took the pickup foot off it. (Mack has a dump body so I just put it all the way up and have nice access to the tank!) Then I cut the little valve off the pickup foot and installed it on the input side of the pump, which was very tight. You can see the input of the pump from the bottom of the foot:


Then I removed the mixing valve thingy from the sending unit and bent the 3/8" feed pipe so that the pump would clear the fuel gauge bracket. Then I ever so carefully measured the proper distance for the bottom of the foot to be from the sending unit top. Dan suggested that I leave a little bit of space between the foot and the bottom of the tank so that the fuel flow isn't too restricted under high demand. Then I cut the stainless steel feed pipe on the sending unit at the right spot, and after drilling out the restrictive check valve on the pump fitting, I welded the fitting to the pipe. Now, my torch welding skills aren't that great and stainless is not easy to weld, so I had lots of pinholes in the weld. So I used some silver brazing rod to cover the holes and put some fuel tank patch epoxy putty over that for good measure:


For the wiring, I drilled through the wire block that the fuel gauge wiring goes through. I measured the diameter of the 14 g wire that I'm using to power the pump and drilled holes as close to that size as possible. I put a little dielectric grease on the wire and it's a snug fit:


Then I built a little "chimney" out of a gear oil bottle to protect the wiring from sloshing fuel (see first pic). This was an important tip from Dan, who said his first wiring broke because it wasn't protected.
I also removed the quick connects outside the tank and used 3/8" injection rated hose in place of the original braided nylon or whatever it was.


Then I used a piece of 5/16" steel tubing to extend the return line away from the pickup inside the tank. I made it about 18" long, toward the back of the tank and put the little red duck bill on the end of it.

While I was working in the tank, I noticed some small black particles on the bottom of the tank. I wasn't sure what they were so I took some out to look at them. Turns out they are small pieces of rust that must have fallen in at some point when I was working on it or got in through the filler somehow. They are magnetic, so I put a strong magnet on the bottom of the tank a few inches away from the pickup foot.

After getting the tank end all buttoned up, I removed the old fuel pump from the frame rail and used a piece of 5/16" injection rated hose in its place, double clamping both ends. Then I tied into the pump wiring harness and extended it back to the new wires coming out of the tank.

Now with this new pump I'm getting 69 psi at idle (with Riffraff FPR spring). Quite a bit better than 55!
This may or may not help with my rough idle, but at least I won't have to worry about fuel pressure now.