Hi All I have a Hitachi ZX350-3 Excavator with 12,000 Hours It has an issue with the boom performance When working the lever for the boom cylinders it is slow and does not perform as normal , if you try to lift the tracks it makes an effort and then stops but if you use both the boom lever and the stick lever then it will lift the tracks off the ground - almost as if you need two functions to act as one Then it will hold the tracks off the ground when all levers are in neutral but if you move the boom lever in any direction it drops to the ground immediately When digging under normal conditions you cannot use two functions at once the hydraulics almost freeze then if you release the levers, you get power back to individual functions When tracking it could track 100 meters normally and suddenly start tracking on one side quicker than the other again if you stop tracking and go again it will start tracking straight Hitachi have come out to the machine and i feel really wasted my time Initially they said it's a proportional solenoid which we replaced, and it made no difference, then they suggested we recondition the two main hydraulic pumps which we did and that has also made no difference Could we possibly have seals bypassing in the hydraulic valve chest ?
Seems like the Hitachi guys that came out didn't properly diagnose it and might have sold you parts you didn't need in addition to the service call that didn't fix anything.
Think I would start checking the pressures, wherever required in the manual for poor hydraulic performance problems.
Here is the monitor guide to help with checking pressures. Record Pump 1 and Pump 2 delivery and control pressure readings with engine rpm and dig mode set to full power with joysticks in neutral and then record the readings again when doing boom down operation. Then raise one track off the ground and fully rotate in one direction and record the pressure readings, repeat for the other track and report back with the values if you can. Best regards
Almost sounds like possibly a load sense issue. Like it's not getting the pressure signal from some functions and the use of another function gets the pump to upstroke.
Hi All Im sorry for opening this thread again but unfortunately 4 months later my excavator is still causing me issues after multiple fitters have attempted repairs Below is the report from Htachi Connected laptop and MPDr, opened troubleshooting program to retrieve fault codes, recorded/assessed codes. Carried out diagnostic for fault code 11307-4: Faulty front pilot pressure sensor or open circuit in harness. Completed ConSite report for findings on Organise parts and tooling for task. Reported to site office, set up for tasks. Removed return and pilot filters and checked for debris, cleaned and replaced filter cover O-ring. Inspected hydraulic tank breather/vent valve. Cleaned oil/debris around the top of control valve, removed main relief to loosen locking nuts, changed O-rings and refitted. Wound main relief up and checked overload reliefs, recorded results, adjusted main relief (high pressure) to 38 MPa, had issues adjusting low pressure relief, could only bring up to 31 MPa. Topped up hydraulic tank with 20 liters of oil. Diagnose boom lower pressure faults. Read up on boom lower circuit of machine and schematics prior to arriving Arrive at machine, significant oil leaks coming from pump suction, spike hoses, upper control valve and lower control valve. Run machine up and check all main relief pressures, pressures were found to be low. Remove main relief and strip to inspect, no abnormalities found on relief valve. Reinstalled and adjustment set to maximum, with relief valve set to max it was found that the overloads seemed to also be set to max, this caused main pump pressure to exceed 49mpa. Attempted to set boom raise overload to spec, upon lowering overload crack pressure it was found that pump 1 was still going to 49mpa and pump 2 to 15mpa. Main relief set back to safe 31mpa to limit the possibility of delaminating hoses bursting, Since this diagnosis The following parts have been repaired to no avail Replaced Solenoid Vale for Pump control Both Pumps have been rebuilt Replace Boom Raise Pilot Pressure Sensor Replaced Relief Valves Resealed both Boom cylinders Resealed main control valve None of these repairs have solved my issue but the dealership have still charge me a heap of money They now want to replace the shuttle valve assembly It seems they want to throw the parts canon at this machine Would appreciate any help
I suggest you try disassembling the components highlighted in yellow in the attached diagram to check if they are stuck or faulty. There are four components that could be causing the symptoms of the boom-down fault.