I need some help. i have a 2000 sierra 4.8. it has been sitting for about 5 years. tried to start it. I have spark but no fuel. I have replaced pump twice, fuel pressure regulator twice, all o rings for injectors and fuel rails. When I turn the key on, I get about 57 pounds on my fp gauge. It drops pretty quick to about 54 and holds there. I am assuming the injectors aren't firing due to lack of pressure. Am I totally off base? Any clue why I am not getting better pressure? Thanks for any help.

 

Yes. It is not a fuel pressure problem.

 

Thank you for the help. I see I have a p1631. I have tried the relearn procedure several times to no avail. Does that passlock system shut off the fuel or do something with the injectors?