Duramax Diesels Forum Truck of the Week
  #1  
Old 08-04-2008, 07:31 PM
02 DMax 02 DMax is offline
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Question LB7 Low Fuel Rail Pressure

I need some help on my 02 LB7 I just had new injectors installed and new fuel filter and new LBZ CP3 with modded fpr and my rail pressure is 9800 psi and drops to 600 psi when going to wot? I dropped out fuel tank tonight to see if pickup screen was blocked and it was clean. Truck is very slow to accelerate. Starts right up no smoke or missing, no codes, rechecked all cp3 lines to make sure they were tight. No fuel smell, no fuel in oil, full of coolant. I am at a complete loss, any suggestions or ideas on what to look for. Thanks for any info!!!
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  #2  
Old 08-04-2008, 07:36 PM
NWTDIESEL NWTDIESEL is offline
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Did you tune the lb7 for the lbz pump? Needs changes made via EFI live.
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  #3  
Old 08-04-2008, 07:43 PM
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NelsonDiesel NelsonDiesel is offline
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possible kinked hose or line to the CP3?

Who installed the pump?
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Old 08-04-2008, 07:51 PM
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If it's a mod'd reg.. I'd say that the plunger is sticking in the bore. Pull it out if you have a chance and bang it against your palm.. If you can't hear the armature banging around then it's stuck. That's the dodge approved method of FCA testing
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  #5  
Old 08-04-2008, 07:55 PM
02 DMax 02 DMax is offline
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Question Low Rail Pressure?

I installed the cp3 myself. Can the fpr be removed without pullin the entire cp3 back out? I bought a new Lb7 regulator and had that modded.
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  #6  
Old 08-04-2008, 08:12 PM
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2500HeavyDuty 2500HeavyDuty is offline
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i might want to ty fixing it with efi first, just changing one table
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  #7  
Old 08-04-2008, 11:35 PM
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beach_33 beach_33 is offline
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i talked to 02 dmax (rick) on the phone and he was having this problem before he installed the modded cp3. the low pressure was the reason for the injector change and the new cp3. i thought that kind of ruled out it being a tunning issue especially since he is running a ppe and it was doing it with the stock cp3. he also told me that a gm diesel tech used a tech2 and that the truck was only commanding 128 mma at full throttle. i sent him here to try to get this figured out. thanks for the help guys
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  #8  
Old 08-05-2008, 07:58 AM
02 DMax 02 DMax is offline
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Question Rail Pressure

What would happen if i unplug the fpr electrical connector and start the truck, i should hear different tone from the motor? Maybe or is this a bad idea?
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  #9  
Old 08-05-2008, 08:23 AM
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Ya if you unplug it you should definately notice whether or not your pumping some good rail pressure.
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  #10  
Old 08-05-2008, 08:02 PM
02 DMax 02 DMax is offline
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Question Low Rail Pressure?

Where is the relief valve on the junction block located on my lb7? I have had two people tell me shim this up by adding two more shims and put it back together.
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  #11  
Old 08-05-2008, 09:23 PM
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Quote:
Originally Posted by 02 DMax View Post
Where is the relief valve on the junction block located on my lb7? I have had two people tell me shim this up by adding two more shims and put it back together.
The relief valve is located on the Y bridge.....I didnt know you could shim them? I just removed the valve and plugged it off

I agree with Brayden on the regulator sticking,you dont have to remove the cp3 to get it out either

It ont hurt to unplug the regulator,And YES it should max out the current on it and make it sound very loud.....if it doesnt then it's probably the valve stuck

there is also a way to check the current,But I suck at electrical stuff
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  #12  
Old 08-06-2008, 07:55 AM
02 DMax 02 DMax is offline
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Default Low Rail Pressure?

Thanks for the info!!! i am going to reinstall the fuel tank tonight and try unplug the fpr and maybe i will just pull the fpr and is there anyway to check to see if it is stuck?
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  #13  
Old 08-06-2008, 06:55 PM
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Brayden Brayden is offline
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bang it on your palm.. if you can't hear it moving it's likely stuck..

Try pulling the connector only first then restart the truck.. Rail pressure should climb to 23,000 -26,000 due to no current @ the solenoid. If it does then it's not the solenoid.

Brayden
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  #14  
Old 08-06-2008, 06:55 PM
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Well... it still could be the solenoid but it's not completely stuck if so.
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  #15  
Old 08-07-2008, 04:21 AM
02 DMax 02 DMax is offline
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Question Low Rail Pressure?

Ok guys i had a brain fart, while watching my rail pressure the desired pressure would only go up to 9800psi on the 120hp setting on my ppe hot +2 and the actual was 1600 psi. I think i have a electrical problem. I am going to remove chip and install on my 01 and check rail pressure on that truck, i know it worked fine on this truck before for the last three months. Does the box on the pass side valve cover control rail pressure? IF so would the box from my 01 work on my 02? The command pressure never went above 9800 psi. I feel bad for not catching this earlier.

Last edited by 02 DMax; 08-07-2008 at 04:24 AM.
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