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Chevy/GMC Duramax 01-04 LB7 Discussion of Chevy and GMC Trucks with LB7 Duramax Turbo Diesel Engines

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Will not build no more that 6000psi in the common rails. With a GM diag. controller we raised the desired pressure to 23,500 and it would not come up higher than 6000psi. The main symptom was when pulling about 12000 lbs. would not run over ... JOIN NOW TO REMOVE TRACER

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  #1  
Old 05-19-2009, 04:33 AM
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Unhappy 2003 LB7 duramax Low fuel pressure

Will not build no more that 6000psi in the common rails. With a GM diag. controller we raised the desired pressure to 23,500 and it would not come up higher than 6000psi. The main symptom was when pulling about 12000 lbs. would not run over 70mph and had NO POWER. Also top speed with no load is about 85mph. Any ideas?
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  #2  
Old 05-19-2009, 04:42 AM
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sounds like you know your stuff, but the obvious . Good fuel filter, pump, etc? How much fuel is your tuning pushing? Might be time to step up to a better cp3 if your tune is suckin a lot of fuel.
I'm sure a lb7 junkie will be able to help you out more and welcome to the site!

FastCR's Sig:1995 Chevy K2500 '95 12 Valve, NV4500, D60, NP205, 215s/SBC (Dyno'd 280.2hp/920.7ft lbs)
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Old 05-19-2009, 07:39 AM
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Originally Posted by FastCR View Post
sounds like you know your stuff, but the obvious . Good fuel filter, pump, etc? How much fuel is your tuning pushing? Might be time to step up to a better cp3 if your tune is suckin a lot of fuel.
I'm sure a lb7 junkie will be able to help you out more and welcome to the site!
The fuel filter is new and the air filter is a AFE open box. Has a 4" exsaust all else is stock. Not sure what (tune) is can you explain?
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Old 05-19-2009, 08:33 AM
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i meant chip, programmer, etc?
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  #5  
Old 05-19-2009, 10:57 AM
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One thing to check that has been a issue is the line going to the cp3, put a clear hose in between and see if there are any bubble/air in the line. I'm guessing there aren't any codes, so the next thing I would check would be to see how much return flow there is. This can be done by the return line going back to the tank, you could have a injector bypassing to much fuel. Also is there any smoke? Both of these would produce a whitish color.
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Old 05-19-2009, 11:15 AM
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you could also check the balance rates of the injectors with the tech 2.
How many miles are on it? the cp3 would have to be really worn out to only hold 6000psi.

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Old 05-19-2009, 11:16 PM
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either the injectors are retuning way to much, cracked bodies on the injectors, or its a very weak cp3. did you get any codes when the tuck would not go over 70mph?

if its cracked injectors you would get lots of fuel dumped into the oil and the oil pressure would drop down severely. but my guess would be the cp3 since you tested it with the tech 2

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  #8  
Old 05-20-2009, 04:42 AM
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Thanks for all the help on this. I have also talked to severl local Diesel Mechanics and they are saying the CP3 is the problem. Price is $600 for the CP3. I think I will be doing the labor and yap, it my first one to do...any sugestions on installing the new CP3?
Also there was one code but I dont remember the number, it said something about low pressure in common rails. All the injecters check good and was balanced between them. The truck has 137K on it and other than NO POWER, it runs, drives and rides GREAT!!! :ok

---AutoMerged DoublePost---

Originally Posted by FastCR View Post
i meant chip, programmer, etc?
After i get past this CP3, what programer do you sugest?

---AutoMerged DoublePost---

Originally Posted by uwyo_dmax View Post
you could also check the balance rates of the injectors with the tech 2.
How many miles are on it? the cp3 would have to be really worn out to only hold 6000psi.
137k and the injectors check good. Balance is real close on all of them.

---AutoMerged DoublePost---

Any sugestions on installing the new CP3?

Last edited by kdxkent; 05-20-2009 at 04:42 AM.. Reason: Automerged Doublepost
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  #9  
Old 05-20-2009, 11:22 AM
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heres some pics of when i replaced my cp3.

cp3 replacement pictures by 2500heavyduty - Photobucket

you will need two new gaskets for the coolant crossover tube that bolts onto the heads and one for the alum inlet on the turbo.

cp3 should come with a new o ring and the nut on the cp3 holding the drive gear on is a 27mm that needs to be impacted off.


in short the fan, alternator bracket, the power steering and ac compressor bracket needs to come off. the thermostat housing and the coolant crossover tubing, oil filler neck, engine wire harness, turbo inlet, and the high pressure fuel lines from the fail need to be removed and the rubber fuel supply and return lines need to be removed. the metal injector return lines nect to the cp3 are gonna have to be unbolted a little bit so can bend them out your way to pull the cp3 out. there's 4 bolts on the front of the engine block holding cp3 it onto it

pulling the cp3 out is a little trick if you can get it pushed out a little bit then you can use two screwdrivers to walk it out and then grab it from the bottom and roll it out towards you.

Last edited by 2500HeavyDuty; 05-20-2009 at 11:30 AM..
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  #10  
Old 05-21-2009, 04:51 AM
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Originally Posted by 2500HeavyDuty View Post
heres some pics of when i replaced my cp3.

cp3 replacement pictures by 2500heavyduty - Photobucket

you will need two new gaskets for the coolant crossover tube that bolts onto the heads and one for the alum inlet on the turbo.

cp3 should come with a new o ring and the nut on the cp3 holding the drive gear on is a 27mm that needs to be impacted off.


in short the fan, alternator bracket, the power steering and <acronym title="Air Conditioning">ac</acronym> compressor bracket needs to come off. the thermostat housing and the coolant crossover tubing, oil filler neck, engine wire harness, turbo inlet, and the high pressure fuel lines from the fail need to be removed and the rubber fuel supply and return lines need to be removed. the metal injector return lines nect to the cp3 are gonna have to be unbolted a little bit so can bend them out your way to pull the cp3 out. there's 4 bolts on the front of the engine block holding cp3 it onto it

pulling the cp3 out is a little trick if you can get it pushed out a little bit then you can use two screwdrivers to walk it out and then grab it from the bottom and roll it out towards you.
Thank you, you really sound like you know your stuff!!! I think before i replace the CP3 I will get it back a TECH II and go thru the injectors again and make sure we didnt miss some thing before I dive in on the pump!!! LOL
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