Originally Posted by F250_

I've lived the long road of using the Baldwin pre-pump filter (the one sold by many as part of the H&H kit), as well as the Carter lift pump between the pre-pump filter and the stock pump suction inlet. From my experiences and lessons learned, I now run the Racor PS120 in place of the Baldwin and there is NO LONGER a lift pump between the PS120 and the stock pump suction inlet.

Over the course of the 8-10 years I ran the originally described "upgraded" configuration (Baldwin plus Carter), I had to replace the Carter pump twice, and remain convinced that my OEM pump's death was earlier than it should have been due to the run periods of extra load imposed on the stock pump's suction when the Carter pumps died.

You see, the fuel pumps used on our diesels are generally (if not always) positive displacement pumps with tight internal clearances, and they generally create excess pressure drop when you have to pull through the non-operating pump.

When the lift pump runs, though, there is no problem, and it actually boosts the pressure on the discharge of your stock pump. Good, right? Yes, and no. Whatever additional pressure you gain by running a lift pump ends up getting lost (more accurately, thrown away) once the fuel gets to the fuel pressure regulator on the fuel bowl in the valley.

So, you may end up feeling better by knowing that the lift pump is boosting your fuel pressure from the stock pump (I know that I felt better -- before the sum of the experience). The bottom line for me is that I've not yet seen or heard of a lift pump scenario where the lift pump outlives the stock pump, and WHEN the lift pump doesn't run, it will most likely result in undue strain on the stock pump which will shorten the stock pump's life.

YMMV