Driving it can drop to ~11 PSI, but sometimes rises to nearly 20, doesn't seem to be directly load related - sometimes it is low going up a hill like the filters are plugged, but then sometimes the pressure is HIGHER going up hill (gentle rollers). This can be within a couple miles, steady interstate travel.
Some times on LONG, flat interstate stretches the pressure will rise and fall about every six to ten seconds (complete cycle, peak to peak).
I parked my truck uphill for a couple of days while I traveled, when I came back the truck needed to crank a bit to start (assume fuel drained back to tank).
No fuel leaks between VP44 and injector crossover tubes.
No fuel leaks that I can find anywhere else.
The couple of oil analyses I've had done came back clean, even after new injectors.
This has been going on for quite some time, but MAY have become more noticeable (or started) when the draw straw was installed - however, there was so much crap caked around the factory sock that pressures were never very high to begin with and probably never even reached 14 PSI.
Was neither better nor worse winter versus summer.
Like an electrical gremlin, this isn't an all-the-time kind of problem, making testing the valve a bit of a crap shoot.
Did this some with the stock steel lines and banjos, does it now with the 3/8" lines and no banjos.
My fuel temps go UP when the pressure is HIGH! Fuel temps go DOWN when my pressure is LOW! To me, this is the biggest clue.
Other Pertinent Info
ISSPRO gauge and sender - yes, sender is on a 1/8" grease hose and not air brake line. There is also the snubber device (fixed orifice).
Fuel filters have been changed numerous times in the time I've noticed this phenomenon (owned the truck a little over 3 years)
Original (to me) lift pump was relocated to frame, then another Carter pump was installed, then a relay was installed to help out the ECM, then the DDRP was installed.
I even 'hotwired' the pump relay direct (bypassed ECM) and went for a spin, same deal.
My hypothesis
I think the overflow valve is "sticky" - it doesn't open until pressure gets a little high, then blasts open and drops the pressure to around 10 PSI when it finally closes again.
Would love some additional opinions on the matter.
So I read this article and would like some input before I spend $40 for a genuine Bosch replacement:
https://mopar1973man.com/cummins/articles.html/24-valve-2nd-generation_50/51_engine/59_fuel/bosch-vp44-injection-pump-overflow-valve-r19/
Symptoms
Other Pertinent Info
My hypothesis
I think the overflow valve is "sticky" - it doesn't open until pressure gets a little high, then blasts open and drops the pressure to around 10 PSI when it finally closes again.
Would love some additional opinions on the matter.