Original pump did about 10-12 at idle and might reach 20 lbs with enough r's. So i got a new one from cummins #4988747 installed it and its about the same? Maybe 15 idle and 25 at higher rpm steady. Ive read to many places it should be 25/35+. I have the new twicked OV from PDP, pressure does not change if i pinch off the rt line either? I can open the cell and thiers pleanty of fuel coming back from the return.?. Pressure is pressure right should you expect to have lower pressure with large injectors? I wouldnt think so right... what gives

 

Update: Today i installed a holley blue inline with the new mechanical lift pump. Fired it up and really didnt notice any pressure diff. still about 12 at idle and 20ish went the r's are brought up some BUT, i got to thinking of this sticker thats on the back of the gauge that says to cut the top of the vent. Its a liquid filled piece like ive worked around for years in the field, those all had the same rubber hat on top and we never cut them due to moistor or such could get inside? Anyways with it running i cut it anyway and a stream of glicerine shot out under pressure and the neddle went to climbing! It now idles at 24# and will go to maybe 38# when reved to a centain rpm, but then the wierd thing if you rev it any past that point it starts to go right back down? Im thinking the pressures now are what i should see with the factory pump only and wondering what it would have been then IF i had cut the vent then. Any thoughts on any of this? Or pressures from someone thats run a electric in front of the lift pump? Seems to sure make bleeding the system a whole lot faster, no more pumping that plunger... Thanks Ryan

 

Your pressures sound good now.
I've never cut the vent open on liquid filled gauges either, the few times I did it made a mess. If a measly 25-35psi made a difference in readings I wonder how far off the unvented gauges I have running at 300 or even 3000 psi are.

 

The drop past an rpm sounds like pump cavitation or a bad spring in the actuator rod- meaning the pump is not keeping up with the cam lobe. Nothing I would worry too much about with the Blue inline.

 

Ya it really surprised me to see the readings change so much by venting a sealed guage?? But it did. I agree the pressures now look ok but they still just look like stock presures should, not a new pump AND a 14# helper pump in place. Right? Ryan

 

Your pressures will only go as high as the OF valve allows.

 

Right i agree but shouldnt it go up when i pinch the RT line shut? It makes no diff. in pressure at all when i do this.. Not even thinking of experimenting but wondering if anyone has ever pluged off the RT totally or at least mostly like with a ball valve, understandably in compitition use only? Im already running the modified OV from PDP, i just fiqured to see the 14# increase from base numbers like i did in my 04.5, i have a H.Blue inline w/ the factory in tank pump and it added the 14# there and on several other trucks i know of. I had just never ran an electric pump feeding a mechanical one before but still think i should see the same result? Thanks Ryan

 

replace your over flow valve... cummins has em..

you can also pull apart and stretch spring back out for a temp fix. if that increases pressure...

overflow valve is located in front of #1 delivery valve on fuel pump

 

With a good lift pump it should hit almost 100psi.
Sounds like your mechanical pump isn't up to par.

Running with the OF closed off could cause very high fuel pressure that blows out internal injection pump seals or even cracking the fuel filter.

 

Well i think alls good now, since i cut the vent off the guage i went back today and tried the pinch the rt line thing and this time it worked! Pressure was in the 50+ range, i pulled the OF valve and pulled it apart. The spring inside was 13mm i stretched it to around 15mm, it now idles at 40psi and will go to about 50 with increased rpm. WOW your saying the factory lift pump should put out 100 psi by itself if the rt is pinched shut? Why then im i still only seeing less than the 60 on my gauge with a new pump and a electric pusher? Ether way i feel much better about it, and suppose i had pleanty of fuel before but didnt know it due to the guage needing to be vented. Thanks guys for the help and advise. Ryan