01 2nd gen cummins 5.9 24v trubo when I bump the start to make the LP(external)start psi goes to 20 when the pump stops the psi drop to 0.I'm checkingthe psi at supply line on the IP.The truck starts hard but seems to run ok do I have a bad check valve somewhere and where?This is my first diesel truck.Thanks for any help

 

Sounds like check valve at vp. What kind of lift pump are you running, could be the lp it self letting it bleed back

 

There is a small hole in the pressure relief valve that is designed to let air out, it will also let fuel out. Bleeding down will happen.

 

thanks for the help order a new VP return line check valve today. Running a stock liftpump hope to do better soon.