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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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  #1  
Old 09-01-2012, 07:08 PM
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Ron Buice
   
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Default Fuel rail pressure

2003 duramax will crank no start, fuel at the bleeder valve. After trying to start I pushed in the rail valve with a screwdriver (don't have a gauge) no pressure, fuel just oozed out. If this is a CP3 problem what else can I check to make sure or what else could it be. Also checked fuses.
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  #2  
Old 09-02-2012, 09:30 AM
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your going to have to put a scanner on it what will show you live data and look at the actual rail pressure during cranking.

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  #3  
Old 09-02-2012, 10:41 AM
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I have tried cranking and pushed the valve on the fuel rail at the same time. No pressure, the only pressure is from what the hand primer pump puts on the system. It seems to be the CP3 pump but I wanted to be sure before I went to that expense and labor.
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  #4  
Old 09-03-2012, 05:01 AM
Diesel Wrench

   

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rail valve? are you talking about the brass valve left of the alternator? if so that is on the suction side if the CP3 and you wont get fuel while cranking unless you have a lift pump. if not enlighten me, i am confused

by the way, ecm needs to see at least 10 Mpa (1450 PSI) for it to fire the injectors. with a scanner check the actual fuel PSI while cranking

try priming till hard, cranking, priming till hard, cranking, priming till hard, etc. do this several times. if it fires then you may be lucky and just had air in the lines. and it may be a simple fix. if not i may be a CP3 or injectors

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  #5  
Old 09-03-2012, 05:20 AM
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Suction side! No wonder no fuel came out, I thought this is where they tested the pressure and no, I don't have a lift pump. I have a friend who has a Tac 2 scanner but he is away for Labor Day. Hopefully this will tell me if the cp3 pump is bad or maybe just a relay. I have done the pump, pump, crank, crank, stuff and a few times it hit a few licks but no start. Trying to think of something to do while I wait on the scanner. Is there a relay somewhere I could check to see if the pump is getting power?
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  #6  
Old 09-03-2012, 05:46 AM
Diesel Wrench

   

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yah, if you where pushing in the valve while cranking all you are doing is sucking in air and making it harder to start. more priming will be needed to help remove the air until the truck starts.


by the way what are you doing up this late. oh wait i should ask myself that

---AutoMerged DoublePost---

The CP3 (fuel pump) is engine driven so no relay. The only power it get is a signal from the ECM that controls the pressure regulator. These do sometimes go bad but try out the easy stuff first as it is a b!tch to get to. It is located in the valley of the engine and takes a lot of work to get it out.

Try putting an air hose in the fuel tank and pressurizeing it to about 5 psi. Do this while another cranks the engine over.

Last edited by 2004LB7; 09-03-2012 at 05:46 AM.. Reason: Automerged Doublepost
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  #7  
Old 09-03-2012, 05:58 AM
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Well, it's 0646 in the morning here in Buford, Georgia. I was up late watching Delta Force, again, but I still wake up early. More info on my truck, last year My diesel friend and I (the go-fer) replaced the #1 injector and it has been running fine ever since. This last deal came on all of a sudden. I had just filled up with fuel and thought it was trash but not much showed when I changed the fuel filter. I even pourded some out and set it on fire to see if would burn. Right after I filled up it started running ruff at Idel, ran fine when I picked up speed then when I got home, about 6mi. it almost went dead in the driveway, shut it off and it hasn't started since.

Guess I am blessed it didn't quit on the road
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  #8  
Old 09-03-2012, 06:13 AM
Diesel Wrench

   

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"I even pourded some out and set it on fire to see if would burn"

Any reason why you did this? Did you think you got water in there? Water will make the injection system go down hill real fast. What kind of filter where you running? Single element? Double coalescing?

Sounds like you got a serious fuel contamination issue on that fill up.
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  #9  
Old 09-03-2012, 06:34 AM
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I thought it might be trash or water, just trying to elimate everything. I bought the fuel at a high volume store (RaceTrac) called them but they had no complaints. I guess it was just by chance it started this problem at the same time I refuled. I wasn't on empty but at $3.99 gal. it took $75 to fill up. I thought about dumping it all but I don't think it's the fuel, looks ok, smells ok, burns pretty good too.
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  #10  
Old 09-03-2012, 02:02 PM
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Will it burn without a wick? Try pouring some into a cup and see if that lights. Straight diesel shouldn't but diesel and gas mix will. Be careful
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