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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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Alright so I have a 03 duramax I am workin on, it literally has 10 miles on it. I am going to the local tech college and it donated from GM 7 years ago. From what I was told there was possibly a bad injector. ... JOIN NOW TO REMOVE TRACER

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Old 12-01-2012, 02:00 AM


Default 03 no start, help

Alright so I have a 03 duramax I am workin on, it literally has 10 miles on it. I am going to the local tech college and it donated from GM 7 years ago. From what I was told there was possibly a bad injector. For the past 6 years it has been threw handfuls of kids trying to get this thing running and nobody can. Last time they tried starting it they literally cranked and cranked to the point they almost burned the starter out. It has now been passed down to me. When I first worked on it today I pulled the oil drain pull and I would guess there was atleast 2 1/2 to 3 gallons of pure diesel fuel that came out before it went to a "chunky" oil. I am letting it drain over the weekend and going to refill it and see if I can get it to roll over. Is there any test I can do with a tech II or something I can command it to do with the tech II to make it fire? I have done a ton of injectors on these trucks before but never used a tech II when I had a no start and am looking for any help or info, before I go and put injectors in it. I should also note when I pulled the bleeder screw on the fuel filter housing I had fuel squirting out on the second pump. Any other test or suggetions are more then welcome, (I am hoping to get it running I could really use the A+ ) Thanks for any help guys!
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Old 12-01-2012, 08:39 PM
Diesel Wrench



The only thing I can think of that may help is to command max fuel mpa. The ecm need to see at least 1450 psi (10 mpa) before it will fire the injectors. Make sure you monitor the fuel pressure.

as a side note, fuel in oil is usually a cracked injector or leaking return line seal dumping fuel into the oil. Get this fixed before trying to start it as you can damage the engine like this.

if the injectors are suffering from high return rates then the cp3 pump will have a hard time building pressure and the engine won't start. The LB7 is not the easiest one the check for on return rates. Try starting the engine with the valve covers off and watch for leaking fuel. If it looks good and no start then check the return rates. once it is good and you get it started then check one last time for any leaking injectors before putting the valve covers back on.

2004LB7's Sig:2004 LB7 Duramax, EFI Live with DSP5 upgraded Tune
stage 4 SC transmission,5" exhaust
160 lift pump, homemade dual fuelers
water injection, 305/70/16 tires
all built up from a salvaged vehicle by me
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Old 12-01-2012, 11:54 PM



Okay so to command max fuel you can just used the tech II and go into like fuel data and maunally make it do it? What should the fuel pressure be once its running?

As far as the leaking return line is it actually a issue with the line its self or as simple as just replacing the bajo washers?
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Old 12-02-2012, 03:24 AM
Diesel Wrench



I have never used the tech ll but I know it can do it, just don't know how. I use efi live to command the ecm for my truck.

Yes, the leaks on return lines are usually just the banjo crush washers. These are supposed to be use once washers so if others have pulled it apart and put it back together with the same ones then the chance of leaking is high.
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Old 12-02-2012, 01:10 PM



Okay. Lets say I max it out and it fires would you lean more towards injectors being bad or CP3? Or is it hard to say without know if is returning too much fuel.
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Old 12-02-2012, 02:04 PM
Diesel Wrench



It is hard to say with out knowing some history on this truck but the LB7s where known to have lots of injector failures. The cp3 Is pretty tough but have been known to fail. With only 10 miles on it it is hard to believe anything could be wrong, yet something is.

instead of commanding max fuel through the tech ll you could always just unplug the regulator harness connector (wires running to the cp3) And that will make the pump go to max psi.

another issue with these engines was air leaks on the filter housing, primer bulb, blender screw, cracked housing, etc keeping the pump from priming. Since it was likely primed a lot, the bulb seals could be shot. If you could pressurize the lines to the filter with a few psi to keep the air out (and possibly find any leaks) this would help in getting it started.
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Old 12-02-2012, 05:32 PM



Sounds good! thanks much for all the info I am going to mess with it first thing in the morning and see what I can do and I'll be sure to give an update.
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