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

04 duramax LB7 cranks but no start

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Old 04-29-2012, 05:07 PM
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Question 04 duramax LB7 cranks but no start

i took my injectors out and cleaned them and replaced one, put everything back together and now it cranks but wont start. I shoot it with ether and it will start but only stays running on ether but not for long. I prime and prime and the primer gets hard and i crank but nothing. prime again and it gets hard and same thing. i checked and have power but no ground to injectors. So i checked the fuel and i have fuel pressure but no fuel to the cylinders. Any ideas on why i dont have ground to the injectors?
 

Last edited by Aceracing86; 04-29-2012 at 05:12 PM. Reason: adding what else i've tried
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Old 04-30-2012, 12:59 AM
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Im sure you have tried this already but you did bleed the air out while priming right? There are two places that you can do it but one is better than the other. The bleed plug on top of the filter hiusing is one but the e is another one. I never knew this until the head diesel mechanic at a dealer told me recently about it. On the passenger side top front of the motor there is a plastic cap almost like what you find on the ac charging connections. Take that off and there is what looks like a needle in a valve stem just bigger. Push that pin in and prime it manually until fuel comes out from where you are pushing the pin. Once it does let go of the pin and then stop priming. Try and start it after that. You mighr have to do it again but its doubtful.

Hope that helps. It really sounds like there is air in the lines. If indeed you are priming without bleeding the air it will never statt.
 
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Old 04-30-2012, 08:27 AM
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thank you for your reply. I actually did that and have fuel flowing now. My problem now is that I have no ground to the injectors. I cant figure out why though. Until I get ground, the injectors wont fire. Any ideas?
 
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Old 04-30-2012, 09:53 AM
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Was everything working fine when you started the job to replace the injector? If so i can only think to recheck all connections including wiring harnesses and actual wiring under the upper and lower valve covers. It would seem like if all connections are good then there are so many things it could be. Fuses, cp3, fuel filter... I really cant think of any more right now. If I think of anything else I will let ya know.
 
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Old 04-30-2012, 03:05 PM
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yea, it would crank hard n skip bad, so i figured i blew a few injectors. but now i have no power and my obd isnt getting power. no power to the dash etc. im thinking its a computer and that it was one of them going the whole time rather than an injector. any way you can think of testing it? i traced the wires and all plugs are connected and no broken wires...
 
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Old 04-30-2012, 04:24 PM
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I had a similar problem years back. The first thing i would do is take a multimeter and check continuity across all fuses both under the hood and on the drivers side fuse box that is in the cab. I always take it back to basics first with the fuses. I am in chicago flying through and my truck is san Diego so I cant reference my fuse box but there is either a relay or a fuse that provides power to the TCM. I am not sure how power is distributed to the injectors but I would assume (dangerous at times I know) that the injectors are controlled and powered by the FICM. Prior to that I am not sure.

I mentioned that i had a similar problem before. When I had this problem it was the TCM believe it or not. I can't remember if it killed my gauges to or not. Its been too long.

So check the fuses if you havent done it yet. don't trust pulling them and looking at them. I have had many fuses that LOOKED good end up being bad. Don't forget the big square fuses. Pretty much have to pull those individually and put your multimeter leads on each blade of the fuse. If you have done any of this or if this is common sense to you then i apologize. Good luck.

Oh yeah, did you disconnect both batteries while doing the work on the injectors or not?
 
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Old 05-01-2012, 08:39 AM
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ive checked all the fuses. im a mechanic so i know what to look for usually...thats my problem, is i can NOT figure out what else it could be. no broken wires, everything is plugged in and yet i still have no ground to my injectors and i lost my obd connection. im completely lost!

yes i disconnected both batteries. the whole nose piece was off. stupid set up if you ask me!
 
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Old 05-01-2012, 11:06 AM
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In that case I would suggest the TCM. When mine went out it literally just quit and for no good reason. I parked it and the next day went to start the truck and it would crank all day long but would never start. That's why I hate the computers on these damn things.
 
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Old 05-01-2012, 04:51 PM
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the only tcm ive ever heard of is for the tranny...i don c how that would have anything to with my obd not working and the fact taht i have no ground to my injectors...i dont know!

---AutoMerged DoublePost---

i dont have any power going into ANY of my computers... and i would normally say thats my pcm, but i dont have power going to my pcm let alone coming back out and going to everything else...
 

Last edited by Aceracing86; 05-01-2012 at 04:53 PM. Reason: Automerged Doublepost
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Old 05-01-2012, 05:16 PM
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I know how it sounds and in itself the TCM is the Transmission Control Module... It didn't make any sense to me then either. But that's what the problem was with mine. Sorry man, good luck.
 


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