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Discussion Starter #1
This issue has probably been beat to death but I have to ask,
When I pump the fuel filter primer it gets hard , then crank the truck, wont start. after cranking, should the primer be soft again?
when I pump it again, it gets hard and there's no visible signs of a leak anywhere. should I be checking the primer seals and o-rings?

The truck had a EGR delete and EFI live, cold air intake and 4" straight pipe. the EGR delete and EFI live have been removed, and replaced with original factory parts The original factory program has been put back in the ECM.
 

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Yes. Fuel is getting to the fuel pumps. It's a vacuum system. When you pump the primer, it creates pressure to the CP3 and what I call the head pump. High pressure pumps like the CP3 need head pressure so that they do not cavitate. I would suspect that your CP3 is broken. It is unable to properly atomize and spray fuel into the cylinder. You should look into CP3 tests. Sorry.
 

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To be fair, the problem is that you're not getting enough high pressure fuel out of the injectors. There could be several causal factors, but the CP3 is what makes the high pressure go to the injectors. You could have a bad bleed off valve, bad fuel pressure regulator, or several other things. There are very good testing procedures in GM manuals, and also very cheap on alldataDIY.com You have quite a mystery, but the end result with a diesel engine is either air or fuel. And because your primer is losing firmness, it seems very much like fuel is being pulled to the engine, but not combusting. Have you checked the oil for fuel? You could also have a bad head gasket. But the fact that it won't run at all leads to a systematic problem. Like the CP3, or bad returns. Hopefully it's just bad returns.
 
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Pump up the primer button till hard and let it sit overnight. Check it in the morning and if it is soft you have a leak
 

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Stupid fuel filter head.
 
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Yeah, as I wait for my next one from eBay to arrive...
 
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Are you opening the fuel pressure relief valve on the filter head and waiting for fuel to squirt from the pressure relief valve while priming it? If not, you're just compressing the air in the fuel line that's preventing the fuel from getting to the rails.
 

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Discussion Starter #9
Pump up the primer button till hard and let it sit overnight. Check it in the morning and if it is soft you have a leak
I pump the primer till hard and 5 minutes later there's no resistance at all, would it lose the pressure and still have no visible sign of a fuel leak?
 

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Discussion Starter #10
Are you opening the fuel pressure relief valve on the filter head and waiting for fuel to squirt from the pressure relief valve while priming it? If not, you're just compressing the air in the fuel line that's preventing the fuel from getting to the rails.
I'll go through the process again to verify the lack air
 

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Discussion Starter #11
I've checked everything I can without the expensive scanner and testing equipment. I may have to bite the bullet and look for someone nearby that can repair this truck.....Thanks for all the suggestions
 

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Add your location to your profile and signature block. Someone may know of a good Duramax mechanic in your area.
 

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Or someone like me with EFI Live that can read a few extras to help out.
 
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