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No start,700psi

JoeTrump

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Hey guys I have a 2004 lb7 and I just put a new cp3 in it and a new fuel pressure relief valve,I had the issue of only about 700psi of fuel rail pressure at crank and then after you stop it drops to 200-190psi,I’ve spent a lot of money and still are short answers. I’ve unplugged the fpr,I’ve unplugged the ficm,I’ve held the fuel system over and over......can someone help?
 
Did you put replace the CP3 and relief valve in to try and fix the low rail pressure Issue? Or did it happen after you replaced them?

Check your supply side for air. Duramax doesn't use a lift pump and are prone to air in the fuel system.

Secondly injectors with a high return rate can cause a no start issue. 15 seconds of crank time I believe the spec is no more than 3ml per injector or return rate. So if you measure at each head total return for each bank shouldn't be over 12ml for 15 seconds of cranking.
 
I replaced the cp3 and relief valve to fix the low rail pressure and bleed off issue,I also just replaced the injectors and it was running with them before,they probably don’t Even
have an hour on them
 
Where did you get your parts at? I've had issues with certain companies in the past. Especially with LB7 injectors. Now I only install Bosch parts unless a customer brings his own.

Since everything is new I would double check your supply system for air. When you open the bleeder and pump the primer it should be a clean stream of fuel with no bubbles. I replace ALOT of fuel filter housings and sending units for sucking air. Ohio salt destroys everything.

If the supply system is good then I would start looking into the high pressure system. You can measure injector return rate that i stated in my other comment. Another good test is to install an injector block off plug at each injector one at a time an look for pressure to come back. Usually I will block off one entire bank at a time on a duramax and if that fixes the loss of pressure then I test that banks injectors one at a time. Saves alot of time doing it that way. Injector block of tools are cheap. There is a guy that makes them and sells them on ebay. All made in the USA 🤘
 
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