I have a 2003 lb7 that won't keep prime. I have to pump primer, open bleeder and let out air, repeat several times before pump gets any pressure. Pickup will then start and run for about one minute before dying. When I go back to the primer pump to try the prime procedure again, the pump is pulled all the way to the bottom. It won't go back up until the bleeder screw is opened. I also noticed that the motor has a lot of blow by.

Any suggestions?

 

sounds like a clogged fuel filter

 

i would say you have air getting in your fuel lines or a filter issue. some times the orings in the primer bulb will wear and suck air in

 

I just bought the truck 4 days ago knowing that it wouldn't stay running. I put an o-ring kit and primer, replaced both fuel lines from primer, and changed the fuel filter, none of which changed anything with the problem. Is there any way to check the high pressure pump? Thank you.

 

if you can get the engine to start then it is not likely that the CP3 is bad, i wouldn't rule out the regulator though.

i would replace the short rubber hose on the output of the fuel filter with a clear one and watch for air bubbles while the engine is running. if you have any then that is the first thing you need to address.

once you have made sure that there is no air getting into the fuel then use a scan tool that cane monitor the actual and desired fuel pressure. the pressures should match pritty closely, if the actual drops to much the engine will die.

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if the bulb pumps fine, after opening the blead screw, then this normaly indicate that the filter is severly plugged or there is another restriction in the line. what happens is that the CP3 ends up pulling a vacuum and sucks the bulb down before it dies

 

pull the inlet line off to the filter housing, put a long piece of fuel line back on with a hose clamp, then put the other end into a bottle of diesel. If the truck will start and run then you know it's clogged,kinked, or pinched before the filter.If it runs then do the same thing at the fuel inlet line next to the brake booster, if running there, could possibly be plugged up with trash at sending unit in tank. if it doesn't run take the outlet line off the filter head and try there. hope this helps.

 

My friend is selling a 2004 GMC 2500 LB7 duramax. He did a lot to the engine but he's now replacing the CP3. it is not running more than 5 minutes. what is my problem. i think I need to bleed the air out with the filter head unit but any suggestion?