I have a 2015 Komatsu PC55MR-2. It is an offshore machine and naturally I have no manuals. There are 3 things that aren't right with the machine. I am not sure if they are directly connected issues so I will lay them out seperately. Issue #1 - The control valve for the dozer blade is malfunctioning. ( I have ordered a used replacement.) Currently the pressure is bypassing the valve and it allows leak down when the blade is up (and no down pressure). Essentially it is circulating fluid = wasted power. Issue #2 - The hydraulics all work normally but at a slightly lower speed, I blame issue #1 for that. Issue #3 - When the hydraulic cylinders on the machine reach their maximum or minimum stroke (in or out) the machine continues to try and push fluid. If I hold the control a little to long I can hear the hydraulic pump draw down the engine and if held too long it will stall out the engine completely. Should the extra hydraulic pressure even be there? Once maximum or minimum cylinder stroke is achieved, should it just bypass that extra pressure and return to the tank? Not sure where to start looking. Do I have too much pressure? Why am I able to keep pushing pressure into a cylinder and stall the machine?
Wow 4 days and no replies. A dead-ended cylinder that slows down and kills the engine is typical of a mal-functioning relief valve. It could even be a crack in the valve body. The problem with a used control valve is it also may have a problem unless the seller can verify that it was working properly. Yours may quite possibly be repairable.
Sorry. I'm not spending every spare moment I have on the machine. As I posted earlier, it behaved much better the other day. At this point I'm waiting for the replacement blade control valve body to arrive before anything else happens. Its a sandbox toy, just pecking away at fixing it up.
A blade that is drifting down is usually a problem with the blade cylinder and not the control valve itself. The pump that makes the blade move is a gear pump so the valve that operates that is an open center valve. That means that oil will always go through it and back to tank as long as it is in the neutral position. As I recall the blade pump has nothing to do with the rest of the implements. The main pumps are part of a closed center load sensing hydraulic system so if the pumps are killing the engine, you have a problem in the main pumps and possibly the engine power output. I would suggest you start over and check the easy and cheap things first, air filters, fuel filters any hidden fuel strainers and such first. The controls for the main pumps will require the services of someone with experience on these machines. I would suggest looking for someone with more experience that you can pay to do some troubleshooting.
Update... I replaced the cab blade control body. It solved the important part of the problem. The blade lifts and still leaks down but much slower. But more importantly it has down pressure and it holds 100%. I drained the hydraulic tank and changed the filter element and that also greatly improved the performance of the machine. The cylinder overload/ engine stalling issue has returned somewhat. I am beginning to think it came with the incorrect oil. Thankfully I bought extra filters and will again drain and change. I have changed the fuel filter but during the priming process I created a leak which I've since fixed but am fighting to reprime. Sometimes its 1 step forward and 2 back.