07 5.9 rail pressure and feed pressure issues

Iron-Hyde

Iron-Hyde

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Aug 11, 2008
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ok, so I am working on a buddy's 07 5.9, we replaced the cp3 with a II 85% over unit last night finally, after the stocker blew out the front seal a month or so ago. He bought the truck off of a forum member here this summer, so I don't know every detail of the truck, but here's a list of pertinent mods:

Wicked Diesel twin kit for stocker over a S475
Mitusa Lift pump
Smarty
DR Performance pressure box (2 pos toggle version)
Flux "90 hp" injectors
now has a II 85% cp3


Now, it doesnt matter how much fuel is in the tank, or which setting the smarty is on, the feed pressure to the cp3 is 15 psi max at idle and at only 30-50% throttle will drop below 10, to about 5 psi and hold there. Its got a rail pressure gauge, so i tried Smarty tune 9 and tune 7 and with the pressure box off and on, WOT pressure holds at 15k psi. I think I should be seeing 22k+ right? I think the rail relief valve is stock unmodded, so i might try to shim it. but that wont affect my feed pressure which i am also concerned about. Mitusa's dont just stop pumping. i haven't looked for the regulator for the LP yet, its not in plain view. do the dodge kits come with one? might it need adjustment?

Thanks,
Tim
 
5psi isnt awful for feed pressure, but its not good either. I would address the feed pressure first, get it up to 15+ at WOT and see what the rp does then. I would also check the RP with a scanner, just because most RP gauges are crap so I dont trust them 100%.
 
other than adjusting the regulator (i assume the dodge kits come with them), how do I get feed pressure up? its a new fuel filter too...

I guess I will try to look at it tonight or tomorrow and see if the set screw for the MITUSA pulley is not tight or missing....maybe that could be it. I just don't see where there can be "no restriction" one day and after driving it for a few months, all of a sudden have an issue. I also don't see how tune 7 and tune 9 resulted in the same WOT RP unless there is a common limiting factor in the high pressure side of the system (aka rail relief valve)

PS: what would a P0148 code tell me other than the obvious, high rail pressure?
 
Unplug the fca and start the truck. Should go to max rp (24kpsi) . If not, remove the return line on top of the PRV and see if fuel is coming out.
 
ok, so I didnt touch anything, I swear! The owner called me this morning saying he drove it around the block and oil/fuel started to come out the breather again (reason why we swapped cp3's)...crankcase is full of fuel now again....if it wasnt the cp3 before, and it isnt the cp3 now (hopefully because he bought it off a member here last week), then what should i look for? i dont think it could be an injector (no knocking, white smoke, rough running or anything)....maybe an injector line?

this thing is driving me to drink....I told him to by a duramax
 
my guess would be the cross over tubes not seated well. If you're sure injectors are good and not leaking down, try wrenching down on the tube nut a bit more. They may just need to be replaced ( which the manual says to do anytime they're out )
 
i havent done a ton of looking around yet.....are the injectors set up like a LB7 dmax where they are under the valve cover and the lines are sealed into the cover? also, I am assuming from your post that the injectors can in fact leak (possibly cracked bodies?) without causing rough running? how hard is it to pull the injectors? and one last question for now, is the crossover tube a injector return line or feed line?

thanks,
Tim
 
Yes, the injectors are under the valve cover but, the feed lines feed into the head via "crossover tubes" to the injector. These tube have to seat in the injectors tightly or fuel will leak and end up in the oil. There could be a cracked tip on a injector but, not likely a cracked body.

This may not even be the problem. The psi relief valve on the rail being bad could cause your lack of rail psi. To check it, pull the bolt and banjo from the top of it. Crank the truck and if fuel is flow out... it needs replaced.
 
Thanks triton. I understand the relief valve could be causing loss of psi, but it won't leak fuel into the crankcase. I really appreciate your explanation of the lines.
 
also you can run the truck with the valve cover off and make the injection pump max out and you can see if fuel is comming out of one of the injectors via cracked body. hopefully the bearings didnt get wiped good luck.
 
ya, i think thats going to be my approach, i dont think it has been running long enough to wipe out the bearings. i know dmax guys who have lost injectors, even pistons, drive 50 miles home and the bearings were ok.
 
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