200 hpdi high pressure fuel pumps

I'm only getting 100-250 psi on the fuel rail... How do I go about properly trobleshooting which high pressure pump (vst or pump assy.) is not working??? Any help will be greatly appreciated...

[boats.net]

Fuel pressure at VST should be about 50 psi, High pressure pump is checked on laptop and is 700 psi on single pump and 1000 psi on dual pump models.

I too am having some kind of fuel problems with a 200 HPDI. The engine will not rev above 600-900 RPM in neutral and maxes out at 4200 RPM @ WOT. I have changed the water seperator, filters, spark plugs, and rebuilt the low pressure fuel pumps. I just ordered a new strainer, but the old one is just 1 year old. My other engine is running fine on the same fuel. Have run YDS @ idle, 900 RPM, & 2100 RPM with no obvious problems. I am running out of ideas (and patience). Any thoughts?
Thanks!