I have Hitachi EX 120 - 2. I have two problems. First problem is that when you operate with heavy load there is a loud chattering sound that sounds like it's coming from either the hydraulic pump or the hydraulic manifold. The sound goes away after after a second or so. The sound will occur with any operation that has a quick response. If you load it slowly with the joystick it will not chatter. It has a new pump coupler. The second problem is the machine when put under heavy load loses power and wants to stall with black smoke this occurs under any operation including trying to turn when traming. The power slowly dies off, black smoke comes on and it will kill the engine. The machine was out of service for quite some time. I've changed all the filters. I also took the newly changed fuel off and check for debris. I found no debris and installed a new fuel filter. No change. Is it possible that both problems could be connected to the differential pressure sensor? I did have a fault code 26. I check voltage at the sensor and adjusted. It will only adjust to 0.79 volts. Specification is .2 to .4 volts max 1.0 volts. The fault code went away after adjusting to .79 volts. If anyone can help me I'd appreciate it, thanks.
I am a Deere guy but the Hitachi's are very similar, exact minus the engine. If this was a Deere I would check the air intake lines leaving the pressure side of the turbo and make sure you are not loosing boost pressure. Now the pump chattering sounds like plate lift but that is only something I would have to hear with my own ear. You hear it once in your life you'll never forget.
If lift plate is chatting what next ?
It could be a suction restriction or could be cavitation well i guess that is the same thing. But it usually means you need pump rebuilt if there is no supply issue. If you drain the tank down do you see any brass in the bottom of the tank. Oh i hope not but when a pump goes there is usually. Might also check the case drain line coming out of the main pump.
This is worth repeating
You might want to check your angle sensor. It is mounted on the side of the hydraulic pump closest to the hydraulic tank. If faulty it will cause your hydraulics to pulse (jerking motion) and will also cause engine to load as it doesn't de - stroke pump flow under operation