I keep getting this low rail pressure code. Truck is really doggy. I have noticed it goes away every so often and the truck runs fine and feels like it has its full power. It seem as though the code will go away in this cold weather for a bit. driving around town it'll usually stay off. but any time you get up to around 50 mph or highway speeds in general it'll kick the light. also under hard acceleration as well. truck starts and runs perfect all the time, just gets really sluggish when the light comes on. its a 2002 lb7 with cali emissions. has 273,7xx miles. Just wondering if anyone has had this problem or has any input. I have access to various scanners (snap-on modis and stuff like that) just haven't had the time to check actual rail pressure yet.

 

after you get above 2k rpms does it feel like it falls on it's face?

 

Not really, its pretty consistent low power throughout the power curve. and then sometimes the CEL is off and it accelerates fine.

 

i thought maybe the injector pump was going out, but that sounds more like some kind of limp mode.

 

with your scanner, monitor the actual fuel pressure and desired pressure. is it consistently lower or does it fluctuate above and below the desired amount? does it drop only under load or high RPM?

with a weak CP3 it will likely be low most of the time or when under load. with a light load but higher RPM the pump may be able to keep up and pressure will be fine.

if it is one or more injectors returning too much fuel then all sorts of pressure problems can happen

truly, the best way to tell if it the pump or injectors is to measure the return fuel coming out of the CP3 and each bank of injectors. this is called a "bottle test" and for the LB7 it sucks to do.

the first thing i would do though is replace the rubber line coming out of the fuel filter with a clear one to see if you are getting any air in the line. air in the lines can be one of the easiest problems to fix but can cause all of these problems

 

Okay I will try this here in the upcoming week or so. ill let you know what I find.

 

Okay, update. I'm really stumped on this one. Using efi live I have data logged the truck. Under full throttle the computer is commanding 22k psi in the rail. I'm only getting 9k. But as soon as I let out of the throttle and my throttle position is zero the rail pressure spikes to 18 or 19 thousand psi. Unplugging the regulator and running the truck showed full pressure. So the cp3 is fine. The actual pressure sticks with the desired until about half throttle then it levels off. I was thinking faulty regulator. So after replacing it the truck still does the same thing. I don't know what to do. Possibly a faulty regulator?


I need help on this big time

 

Sounds like your not picking up enough fuel ... when was the last time you changed the fuel filter? Might wanna change it again and fill it with seafoam or some sort of injection cleaner for a diesel, not sure what is best for the duramax, if it were a cummins or PSD i would just use Dextron atf ...

 

I just changed the filter little more than a month ago. Although I may try and run some atf through it..

 

Couldnt hurt to change again .. you may have gotten some dirty fuel ..?