Jc , and get your self a Gauge ,I know it wont see fuel pressure that would be separate Idem , but it will look at the other things to help you resolve , Take a look at Riff raff diesel product for the Blue spring.
The way the injector works on the fuel side is there is an intensifier
piston. That piston if the fuel pressure is low will bottom out at the
of the stroke and hit. What the right pressure does is keep the chamber
full or part full so that the piston does not hit at the end of the compression
stroke. The piston is driven by high pressure oil from the HPOP and controlled
by the FICM. It is returned by spring and fuel pressure.
So if you running so the demand for fuel is high and the supply pressure
is low the intensifier piston will bottom at the end. That is hard on both
the spring and the piston.