Ive been chasing down a low power and abysmal (10mpg) fuel economy problem and I think Im a step closer. I installed a westach gauge and sender and it shows 10-12PSI at idle. The funny thing is that up near 2k RPM sometimes it will show a better reading.. something like 22 or 24PSI. most of the time it will stay put at 12PSI. I confirmed these readings with a quick driveway test and a fuel pressure gauge (one made for fuel and not air pressure this time) and they look right.
Have any of you folks had a 12V with a lift pump thats on the way out and sometimes gives good readings? Kind of like a stumbling idle on an old motor where you might get good compression on a stroke or two and it sounds good, but otherwise its low.
How hard are these pumps to swap out myself? My preferred diesel shop is real busy at the moment and it sounds like a small job (but hes getting my transmission work for sure). It just looks like a real beast to get to on the side of the block like that.
Its this guy here, right? :
http://www.citydiesel.net/supply-pum...cPath=22_26_48

 

It's easy to tell if the lift pump or overflow valve is the problem.
Just squeeze the return line with pliers with the engine running while watching the fp gauge. If the pressure goes up the OF valve is the problem, if not it's the lift pump or a restriction in the supply-- plugged filters or kink in a line.

 

I took the overflow valve out and cleaned / measured it and it looked ok. the spring was 1/2" uncompressed.
Looks like the return line is a bit dry-rotted wonder if that would be a problem
trying to decide whether to swap this myself. That lift pump in the link look like the right one?

 

Ok, I went by the local cummins dealer and picked up an overflow valve that the guy looked up and matched to the application. The opening at the bottom of the valve is much smaller than my old one, and the internals are much different. The old one had a little cup between the bearing and spring and the new one doesnt have that, but does have 3 different sized shims on top of the spring.
I get entirely different readings now. 28psi at idle of 750rpm and about 20psi at the lowest point at full boogie. Another oddball thing is I get no visible smoke with all these mods.
Anyone have any ideas? Im stumped!