Rail Pressure Issues

[dmaxdallas]

Hey guys,

Looking to see if anyone has any insight into what's going on here with my truck. It gets garaged for the winter and I've been chasing this problem for the last few weeks every time I've started it or went to drive it.

The issue is intermittent, about 60% of the time it acts up. Basically the problem is that when I go to crank the truck over, it makes max rail pressure even though it’s commanding the appropriate rail pressure. While I can get the truck started with max rail pressure, I usually give up as it’s incredibly rough to start and runs awful obviously when in this condition. I took some pictures of my CTS displaying actual rail pressure and desired rail pressure and those are shown below, both of these were with key on and truck not running after having cranked for a second and realizing the issue had arisen again.

The codes on the truck which I pulled via an Autocal and the CTS are as follows, with no check engine light illumination when running:

PCM – P0670
ABS – C0055
UNK – B2610

(these two accel pedal codes are very random and only read on the CTS when they do appear)

PCM – P2138
PCM – P2140

I am starting to lean towards the CP3’s metering unit (fpr) being the problem and potentially sticking causing the max rail pressure issues; however, the weird thing is that about half the time the truck will start and run perfect, I even took it out for a few miles a couple days ago without any hiccups, in total the truck ran and idled for about 3 hours straight.

I wanted to see if any of you had any other ideas or further insight before I started tearing the truck back apart. I also have access to a Tech2 if there are any further tests/checks anyone would recommend I try to help diagnose my issue.

Thanks in Advance for any Help!
Dallas

 

[Burn Down]

Fpr would be where I would start.

 

[millerman04]

Check the plug on the fuel pressure regulator. Mine had a loose power wire. Mine also was random, meaning one day it ran fine, and the next it had max fuel pressure. Come to find out the power wire was coming loose from the plug itself. Made for a big headache to figure out. Start the truck up, and wiggle the wires going into the plug, and see if there's an idle change. Good luck

 

[dmaxdallas]

Check the plug on the fuel pressure regulator. Mine had a loose power wire. Mine also was random, meaning one day it ran fine, and the next it had max fuel pressure. Come to find out the power wire was coming loose from the plug itself. Made for a big headache to figure out. Start the truck up, and wiggle the wires going into the plug, and see if there's an idle change. Good luck

Thanks for the info, I'll give that a try!

 

[dmaxdallas]

Well a little bit of an update here. I replaced the connector with a new one from work. Still didn't solve my issue.

I payed a little closer attention this time before cranking the truck over and noticed something odd. Even before I cranked the truck at all, just as a piece of information the truck has been sitting for two days untouched now, I noticed that my CTS was already displaying the actual rail pressure as 26k psi. Maybe I'm missing something here but I have a hard time seeing how the rail pressure would already be max without having spun the cp3 at all. Once again the desired rail pressure read an appropriate value, so I'm pretty confused.

Starting to lean towards just tearing into it and swapping fpr, but will be pretty upset if the issue is still something else like an electrical gremlin. Once again any thoughts/ideas would be appreciated.

Thanks for reading
Dallas

 

[IOWA LLY]

You have an issue with the rail pressure sensor, or the wiring going to it.

There is no way your rail pressure is more then a few hundred psi with the engine off, and not cranking. So if it's reading that high it's a faulty sensor or wiring. It's not something in the cp3 or fuel pressure regulator. In my opinion.

Sent from my SM-N920V using Tapatalk

 

[dmaxdallas]

You have an issue with the rail pressure sensor, or the wiring going to it.

There is no way your rail pressure is more then a few hundred psi with the engine off, and not cranking. So if it's reading that high it's a faulty sensor or wiring. It's not something in the cp3 or fuel pressure regulator. In my opinion.

Sent from my SM-N920V using Tapatalk

Sort of why I was so hesitant to believe the fpr was sticking, I'll go through that section of the harness and see what I can find out

 

[Burn Down]

That last bit of info would have been helpful... I agree with Iowa, rail sensor or wiring.

 

[millerman04]

I hafta agree too. That does make sense. :thumb:

 

[chandler583]

When my rail pressure sensor was bad, it didn't want to run at all. In fact, the CP3 was over pressurizing the rails and causing the relief valve to pop off. Not sure what the actual pressure displayed, but replacing that sensor fixed the issue immediately.

 

[2004LB7]

disconnect the pressure regulator and CP3 will push max PSI

disconnect pressure sensor and it will show max PSI

this can look like the same problem but as it has already been pointed out, if the truck is not running and the pressure is still maxed out then suspect the pressure sensor or wiring. if it jumps up to max after starting then it is in the regulator or wiring

 

[dmaxdallas]

Just an update guys, sorry I haven’t posted in a while, wanted some time to pass before I spoke too soon on the rail pressure issue being resolved. I replaced the rail pressure sensor BDK connector with a new one and fresh pins. Also disconnected and reconnected all ECU connections and since then the truck has behaved completely normal, running well and tracking rail pressure properly. Thank you everyone for your input and help! I’m now on to the next potential issue….


http://www.duramaxdiesels.com/forum/showthread.php?p=994569#post994569

 

[2004LB7]

Thanks for the update. Glad you got it figured out