2001 lb7 stock. Crank no start without priming then dies. Desired frp is 42 mpa, actual frp is 20 when it starts then drops to 12 and dies. inlet of cp3 pulls no vacuum.
The only way to raise the actual frp is block the return on the cp3 then it stays running for a little longer. Bad cp3?

 

Sounds more like an air leak.

If you prime it before trying the first start does it stay running?

 

No air leak, prime it, it will start and die but supply line to cp3 still has pressure on it from the primer, it won't pull a vacuum.

 

This would suggest a fuel supply issue. Were there any symptoms leading up to the issue?
Any DTC's?

 

I have fuel at the cp3, no air between it and the filter but the cp3 won't pull any vacuum. I even checked it right at the inlet on the cp3 itself.

 

Do you have an EFILive V2?

 

No efi live. Using a snapon versus.

 

I dont use that scan tool myself so I am not sure what capabilities it has. I know in EFILive we can go into bi-directional control, then command the pump to full rail, then log it and see if it can keep up. In my previous LB7 I was making a peak of 12,000 psi when commanding around 23k psi.

 

It does, even then I can only raise the pressure if the return on the cp3 is blocked.

 

Bit the bullet and pulled it last night. The shaft is broken in the cp3. Will post if that fixes all the issues or not.