I suggest starting all over from the beginning. I'll bet (since this has been going on for 2 years) that you and your tech have gotten tunnel vision and are overlooking something...……..yes, we all have done it so don't feel bad.
Start with your engine first! It is the power that drives your hydraulic system and weak performance will directly effect your hydraulics. Register full high idle rpms and do they meet the manufacturers specs? Hydraulic stall specs? Full stall if applicable? When under stall, do you see exhaust smoke? What color is it? does it seem excessive? Can your hear the turbocharger wind up? Until all of your engine parameters are met, you are wasting your time testing anything hydraulically.
If the engine checks out, then move to the hydraulic portion and start with your pump system. The pump not only creates pressure, but creates flow. Is your hydraulics slow?...or no power?....or both? Run the machine through each function and take notice as to whether there are any noises? Do all the functions have the same symptom? Are they all slow with no power?.....or do other functions seem normal and others dont?
Although a main pressure test may see relief pressure, your flow may be down which would cause the hydraulics to be slow. Does the main pressure relief meet specs? What is the pressure reading? Is the main pressure reading the same with each function? Is there any unusual noises when the relief is open (outside of the normal sound of a relief)? The best way to determine pump condition would be the use of a flow meter. Your Hitachi guy should have one, and should have all the specs for the pump.................I would do this FIRST thing Hydraulically. If you dont, the system could have you chasing your tail.
If your pump checks out, then its control valve time. Check the above engine and pump out. If those check out with real data info posted here, then we can move on to more troubleshooting.
There is plenty of knowlege here to help you get most problems figured out........But we need real and specific data and information to get anywhere.
