Hello I have been working on a ex120-3 for the past 3 months and cannot figure out the route of the issues. I have the manual for the machine and have worked on others in the past. What I understand with these machines is serious electrical problems in the harness bein and fault out all sensors and computers. This machine started out with a very slow hydraulics problem. After poking around I found the problem was in the main harness. Got the machine to my shop and replaced the harness. This took care of the slow function problem but an entirely new problem came up. As many times with these machine the biggest problem they seem to have is this stalling when any function is bottomed. Here's what I have done to remedy this since then. Replaced with genuine hitachi parts - MAIN WIRING HARNESS - CAB WIRING HARNESS -PVC COMPUTER - EC COMPUTER - ANGLE SENSOR - DP SENSOR - SPEED SENSOR - PUMP PRESSURE SENSOR The only things not replaced is the two high speed pump SOLENOIDS due to being replaced about a year ago by John Deere dealer. I did test them multiple times as well to be sure they test to the spec in the book and they check out every time, I also have disassembled them to check the internal parts and could not see any damage. If someone has any other ideas I would really really appreciate any help. Thanks for reading.
Engine speed sensor has nice square wave?
I believe so. Another thing to add is every time I've tested the angle sensor both the new and old one I can only get a maximum of 1.7volts out of it. I know it is supposed to be at 4.5 so this has me stumped after adjusting everything else to spec and replacing almost all electrical. What would make that sensor not able to output anymore than the 1.7 volts?
Supply voltage is too low Sorry, I meant the loaded supply voltage is too low. Did you clean all the connections including the fuse terminals
The cab And pump harness are both brand new and cab harness comes with new fuse panel and all The supply voltage to the sensors all checks out at 5 volts It's just the output of the new angle sensor will not go above 1.7V
Could be a bad angle sensor that seams to be the only part is causing problem.you have good voltage in but bad out.I would try a different one.
At pump solenoids do you have 24v when engine stalls. Also is engine under load when problem is happening with no functions activated?
Yes i have 24V at the two solenoids even when machine is in stalling mode. I also have tested for the ground signals from the PVC to the solenoids and also have good signal. Now for the engine under load, The engine itself is not under load but i can put it to load the pump by moving the angle sensor forward and back. I checked the machine again today and tested the sensor voltage while machine is running and also while holding a function to relief. What i am getting is never more than 1.5Volts out of the angle sensor and it is only between 1-1.5Volts maximum output. This angle sensor is Brand New OEM Part. What i am trying to understand is why the voltage is not adjusting to the 4.5Volts needed. What exactly is the angle sensor output voltage in line with or coming from to get the 4.5V?
Is the dimple opposite the harness on sensor and is the spring clip in pump tight on sensor and usually I leave solenoid disconnect for 5 min. and you can here pump load up and adjust angle volts. I know you already now all this just asking? If all is fine possible internal pump linkage binding. Did you try and leave sensor off p ump and see if you can adjust by turning shaft of sensor.
try to replace your pump solenoid. replace it with a genuine part.
So I replaced both pump SOLENOIDS today as a last ditch effort to remedy this machine. Turns out they are not the problem either. Somehow I did notice about a half a volt change in the angle sensor output. It has been reading only 1.5 or so max but it went up to 2V. What I did take note of was the way the SOLENOIDS were Turing on and off very erraticly. It seems as if the computer cannot send the correct signals to them because I am watching the pressure reducing valve coming on and off through the pilot hose to the pump and it's all over the place. So u can almost really watch the signals the computer is putting out by watching the hose go crazy. As I said before both computers brand new, as well as all sensors and harnesses. Anyone know where else the signal to the SOLENOIDS originates from if not just the PVC computer? On another note you can also feel the uneven control signals if you track the machine, it will track fast then slow erratically as well.
to see the problem clearly you need to use the dr. zx. observing without seeing the system is still considered blind. sorry but that's the only last thing you can do. by using dr zx. you can monitor the angle sensor, dp sensor, pressure sensor, RPM sensors and all other sensors you can see if this sensors are working in dr zx. as you said all parts are new.
Yes I will need to get my hands on one. I think this machine will be leaving my shop anyways and going to somewhere else. I hate to ever give up on a repair but this one just has me stumped. The only other answer that popped in my head that it may be is the new harness itself. Maybe some wiring got moved or twisted the wrong way when installing thru all the frame holes and what not but I just can't lose anymore time and money to chance replacing that again. This will prob be the last hitachi I try and repair electrically lol