What IS the required fuel pressure for the 5.9 24V? Almost every lift pump that I look at has a 2-6 or 3-8 PSI rating. From what I read the Cummins is 12-15 @ idle PSI so why is that so high? I think the huge semi engins are still low pressure pumps and marine engines all have the low pressure pumps so what gives?

 

Present wisdom is that it's best to stay above 7-8 psi at all times.
Stock idle, with a good lift pump and a healthy VP-44 Injector Pump is 12-14 psi.

RJ

 

Very long debates have been had about this topic. I think the results bear this out: Anything over 1psi to the VP is still positive pressure at the IP inlet, but more is better. The VP bypass opens up at 14psi so, by deductive reasoning, 15psi at all times would be awesome since you have the most fuel pressure that the IP wants. I personally have my LP bypass set at 24psi before the fuel filter and see 22psi at the IP. I also don't want to see the psi drop to nothing at WOT. Confused yet?...

 

Now you started the VP PSI war,,
i also think 10 PSI at all times is minimum. the Fuel Boss is in the mail.

 

Are those engine running VP pumps as well? Different pumps require different suction pressures. The P-pumps are 25-40 psi. So its not all apples to apples.