Hello! just got a PC 78 MR-6 excavator. Trying to figure out what is going on with it. It doesnt have power to run the functions. just kills the engine. It seems like its trying to go to fast maybe? Seems to get worse as it warms up. Changed all the filters. Any other ideas?
Hello, You may need to be a little more clear with your wording. I will assume by 'power' you mean fuel/mechanical power not electrical, and by 'functions' you mean mechanical/hydraulic. I'd like to say I'm no expert, but have learnt a bit from my own problems on my own machine. It sounds to me like your pump may be stuffed, or you have a blockage somewhere in the valveblock. The engine uses diesel power to turn the pump, which will pump hydraulic fluid from the tank through the valve block and on to various functions before returning to tank via the valve block. Find the main hydraulic hose that leads from your pump to the valve block, when the engine is running and safety lever forward, go and feel this hose and make sure you can feel it is under pressure, if it is, that is good, and your pump should be ok. I would then begin to think the problem may lie in the valve block. Do some functions work better than others or are they all affected? If all affected equally, there is a blockage in the main return line to tank somwhere that is restricting hydraulic flow and putting engine under load. This high revving sound you mention however makes me think that the pump is damaged and the engine is spinning a pump that is free spinning, ie not pumping fluid effectively.
Thanks for the reply. sorry i wasnt more clear. The engine is stalling under load. if i stick the bucket in the ground and try to dig or hit the end of the cylinder it just kills the engine. It seems to be mostly on retracting the cylinders. Extending seems to be ok. If I understand right it should bypass oil or go through a relief valve instead of killing the engine? This is what it feels to me it is not doing. Is this controlled by computer or is it mechanical? Hope this makes sense!
Those machines are load sensing so start with the basics. Make sure the air cleaner is not plugged. Make sure the fuel system is clean and not plugged at any water separator, fuel strainer or fuel filter. Have you check to see if there are any fault codes on the monitor? Have you tried any other combinations of operation. Does the machine travel in a straight line? Can you operate two functions at the same time and it works? Does the swing function seem to work properly? I don't have a book for that model of machine so can't provide much more than the basics.
I believe the air filter and fuel is good. Had that all apart. Driving seems ok as does the swing function. It does not multi task withwit stalling. The only code I sometimes get is the swing angle sensor. Thanks!
i don't think relief pressures are the problem, they are usually high enough to still bog your engine down. If your pump is pressurising the main feed into valve block, Something is restricting the hydraulic circuit. Blocked Filters, sticking valves, corrosion in the ports,. Carefully test every function, to see if the problem is isolated to specific circuits, or the whole hydraulic circuit. I am assuming here that the engine itself is not the cause.
I don't know the system in your machine but older Dash 5 machines had that issue with a straight travel valve. Small machines shifted the valve with pressure switches tied to the travel circuits. Basically when you are traveling and operate something else the straight travel spool would shift joining both pump circuits so the machine might slow down but the travel would stay straight. If the valve was shifted while only working one function it would stop flow to that side of the valve and since the oil had nowhere to go it just went over relief. A photograph of your valve area might let me know what kind of system you have, open centered or closed center. Anyone with a hydraulic circuit diagram willing to share would be appreciated.
Played around with it some more. It definitely gets worse as it warms up. Works perfect cold. it also works fine when driving. Sounds like its deadheading when it hits the end of the cylinder. Once in a while it will all at once work good for half a minute . Sorry didnt get a photo. it looks like a closed center system to me. Thanks for the replies!
Sounds like the regulator in the pump most likely pump rebuild time
So the main difference between warm and cold is the viscosity of the hydraulic fluid. Cold thick hydraulic fluid pumps with higher pressure and therefore better workload, Warm thin fluid has less pressure and less ability to do work. I wonder if you go into your computer settings and check your RPM vs what the rpm should be for given functions. If RPM higher than that stated in the manual I would think pump issue. I purchased an online workshop manual for my Js240 off EBay, very cheap. Everything you need to know is there about which buttons to press and hold to enter into the computer for diagnostic check.
Did you figure out what was the problem?
I also have a 2008 PC88MR-6 excavator that kills the engine after the oil heats up. I checked the engine and it's ok. The pressure distributor looks fine, so I removed the main pump. In the oil I found a little span / metal filing. The hydraulic diagram shows two pumps, but there is only one with two outlets. Yes, there was a problem with the pump, a lot of wear and tear. My client will decide if we replace the all subassembly ($ 4000 OE + shipping + taxes), or he wants a repair.