LB7: Low rail pressure

[Gya0ma7ha]

Hey guys, i'm a regular over at d-forum and had a question i wanted to post here as well. I'm having low rail pressure issues, like 16,000 at 1450us, which is stock. So, i'm thinking i need a new cp3. But, i was wondering if a lift pump or a new fprv could help. Any thoughts? Also, if anyone has a CP3 that will work on my LB7, let me know. Thanks.

 

[Kat]

:hello: and :welcome5:

Moved your thread here :thumb:

 

[Whitetail Addict]

Another possibility could be the injectors causing the drain in rail psi.

Welcome to DD.

 

[Gya0ma7ha]

Another possibility could be the injectors causing the drain in rail psi.

Welcome to DD.

Ya, but with stock injectors and all balance rates between -1 and 1, i wouldnt think they are the culprit.

 

[SDE]

How many miles on the truck and on the injectors?
New fuel filter?
Have you checked to see how much vacuum your pulling from the tank?
Do you have access to a Tech 2 or EFI to do a Pump Test?

Just questions to help get you in the right direction. :hug:

Spencer

 

[TrentNell]

I would do a bottle test first , and if the return rates come back OK then I would think the the CP3 to be the culprit .

 

[Gya0ma7ha]

I would do a bottle test first , and if the return rates come back OK then I would think the the CP3 to be the culprit .

Ya, i have heard of this bottle test before, if you have a link, that would be great. I'm thinking it's the cp3 as well. I have a new fuel filter on it. the truck has 176,000 on her, so she is not young.

 

[Gya0ma7ha]

How many miles on the truck and on the injectors?
New fuel filter?
Have you checked to see how much vacuum your pulling from the tank?
Do you have access to a Tech 2 or EFI to do a Pump Test?

Just questions to help get you in the right direction. :hug:

Spencer

I have EFILive and am pretty familiar with it, do you mind explaining what a pump test is for me? Thanks a bunch.

 

[2500HeavyDuty]

How many miles on the truck and on the injectors?
New fuel filter?
Have you checked to see how much vacuum your pulling from the tank?
Do you have access to a Tech 2 or EFI to do a Pump Test?

Just questions to help get you in the right direction. :hug:

Spencer

I have EFILive and am pretty familiar with it, do you mind explaining what a pump test is for me? Thanks a bunch.

you can open up your scan tool, connect to your vehicle, and go to the DTV tab (F12), target the lb7 duramax diesel ecm, and click on the Control tab below.

from there click on the desired rail pressure control and command 160mpa.

make sure you are logging your actual and desired rail pressure and observe the actual rail pressure under the Data tab (F9)

 

[Gya0ma7ha]

you can open up your scan tool, connect to your vehicle, and go to the DTV tab (F12), target the lb7 duramax diesel ecm, and click on the Control tab below.

from there click on the desired rail pressure control and command 160mpa.

make sure you are logging your actual and desired rail pressure and observe the actual rail pressure under the Data tab (F9)

Well, i have logged my actfrp and desfpr, desired at stock is like 23k and im only getting like 16k.

 

[2500HeavyDuty]

well, weak cp3 or injectors. most likey cp3 the way your injectors are looking based on your balence rate test.

im not famiilir with the bottle lest on the lb7, but for the ammont of work needed to test the fprv it can be shimmed or plugged too.

 

[Gya0ma7ha]

well, weak cp3 or injectors. most likey cp3 the way your injectors are looking based on your balence rate test.

im not famiilir with the bottle lest on the lb7, but for the ammont of work needed to test the fprv it can be shimmed or plugged too.

Ya, i was curious as to whether the fprv could have something to do with this.

 

[2500HeavyDuty]

its worth a shot. it only costs $0.18 to shim it, and like 15 cents to plug it if you have a tap and die set.

 

[Gya0ma7ha]

Ya, and how much time? I think im going to give it a shot.:thumb:

 

[2500HeavyDuty]

wait i do take my last statement back, you have 170k miles on the truck?

i do doubt you will get a significant gain in rail pressure that you are hoping for. if you want to try it though the amount of time needed to do the mod is about as long as it takes you to pull off your turbo intake horn +15 minutes and re-installation.

the mod does work well with a new cp3 and higher rail pressures. doing the mod will eliminate one probable cause though.

 

[Gya0ma7ha]

I might as well try to get a CP3 out of a wrecked or used truck.

 

[05lly2500hd]

ever fix?

 

[DIESELJEFF]

I have the same issue going on. I did the cp3 test today and it only gives me 15800 psi when i command the full 160mpa. If i give it a little touch on the go pedal to raise the rpms then the psi will start to come up. In fact the max reads at 25000. Is there anything else that i can test before i tear into the cp3?