I am having problems with low rail pressure. Now I have my gauges installed, the max I have seen at WOT is 22000 very breifly, and then it drops to 18k when the truck shifts up a gear. It will sometimes throw a p0148 code, and will sometimes only reach between 12-15K at WOT when I really get on it accelerating hard onto the freeway. The rest of the time it seems to run fine, no smoke at all, no knocks or rattles (from injectors). Oil level staying constant.
So far I have changed my COV, PRV, Rail pressure sensor, Lift pump(upgraded to a raptor 100 which delivers at least 8psi when I get on it, 17psi at idle). I have disconnected the FCA and then started the truck.....rail pressure stays at 5k and idles normally (maybe a very small 'rattle'). From what I have read, this should cause my rail pressure to peg to max on my gauge.....this leads me to believe that I may be looking at a new CP3, and that my problem is not my FCA. Any ideas?......I'm close to fixing this thing with a couple of gallons of diesel if you know what I mean.
ANy help would be greatly appreciated, I need to get this thing fixed ASAP as it is my DD for work. Thanks in advance.
Paul
______________

 

If you haven't replaced the FCA, didn't see where you did it, thats a good next step before the CP-3. The rail pressure should max out by disconnecting the FCA if it is not jammed or sticky.

 

Just ordered an FCA, hopefully that will take care of my problem, if not then i guess it's time for a new CP3.

 

like he said just unplug the fca and start. it should peg the 30,000 gauge

 

tried that, changes nothing, pressure stays at 5k at idle with slight rattle.

 

so I think I have cracked the problem, I re-torqued my injector tubes and it now hits full rail pressure at WOT no problem,can I say just WOW!!!!, I've also not had my CEL come in for the last 4 days, even when driving it like I stole it, to purposely try to get the light to come on.
So to all of you out there seeing the dreaded po148 or po251......before you change anything (FCA,COV, rail pressure sensor) try doing what I did and torque down those tubes, it's pretty much free to do (apart from a $5 gasket for the intake horn), and only takes a couple of hours. Pretty much anyone who knows one end of a wrench from another would be able to do it too.
One tip is to CAREFULLY pressure clean around your rail the day before you do it, so as to reduce the likely hood of getting dirt in your system, before you do this, smear all your electrical connectors nearby with a good coating of di-lectric grease to prevent water ingress.
I would also recommend getting a fuel and rail pressure guage....yes this will set you back around $300, but that is still only what it would cost you for around 2 hours at the shop. Bear in mind that my local dealership wanted $750 just to run through the test process to diagnose my problem...then I would of had to add labor and parts on to that....my total outlay, with all my parts, plus the guages came to around that, so at least i'm not out of pocket there....just have parts I did not really need, and a couple of gauges that will let me know if I have any future problems brewing with my fuel system, oh yeah, and I learned a ton about common rail systems
Hope this helps someone to avoid the frustration I went through, and thanks to all of those who offered advice.
Paul

 

Had the same problem you discussed, tightened the injector tubes and have been trouble free for a year almost!!! Very satisfying feeling when you fix it yourself!!!

 

I would also suggest testing the PLV. Simple to do and I have seen trucks bought back buy dealer because mechanic over looked this easy fuel system test.

 

Some old grey-headed mechanic asked me if i had replaced the pre-filter in the tank......i answered no......he unrelented.
I pulled the transfer pump out of the tank, took the plastic pump cradle apart and COULD NOT BELIEVE HOW FUEL WAS GETTING TO THE PUMP!!!!
It was clogged beyond recognition......cleaned it.....solved my fuel rail problem.

 

What year was the truck?