G'day Mate,
I would have thought that other people more in touch with the particular machine than me would have jumped on you with help by now so I will try to give you a start.
I guess the machine is Hitachi. How old? We sometimes have them named differently in Australia but I don't remember any EX270's.
If whoever rebuilt your main pumps was fully capable of doing so, they should have properly set-up their flow/pressure control curves either on the machine, or on a test bench before leaving their workshop, so they should be able to troubleshoot your problem.
What condition was the pump group in before overhaul?
Depending on your answers and comments,and without seeing the circuit diagram for the machine, I would tip that you have:-
a) A pump controller problem.
b) A computer or sensor problem
and/or
c) A logic-element playing up.
Hope this helps.
