And by all means, if it is common rail syatem, do not loosen injector lines or any metal lines for fuel.I have an h45 z that had a lower fuel pump pressure and were replacing lower fuel pump, and replacing all plastic t's in fuel lines with brass t's, And rubber fuel lines, If you replace fuel lines, be sure to only use what is 250 psi for injector systems. Remove right side cover, and right above lower fuel pump is a clear tube. see if fuel is flowing through it. Hope this helps, just trying to give you ideas. for 2 to go down at once could be fuel contamination