My rig 790ELC is staying on high prssure to the point it is overheating and won't rev up freely. It has less load on it using functions. I changed the output pressure sensor as fiddling with its connection had seemed to help before but it made no difference. I'm afraid it is something in the computer controls but want to do what I can before calling a dealer. I pulled both computers and the red lights are blinking steady with no Morse pattern. From reading here they are known for gremlins. Anyone run into this problem before?
A little more info that has come to mind. I had a battery blow up on it and have had some screwy but short term issues since then. The four button speed control changed positions for a short time (first went to high but stayed in order) but on restart went back to normal. I may be regretting buying a Hitachi as there are many pages just dealing with electrical problems with no good answers. So far none have been for it going to high pressure and staying there. I can unplug the outlet pressure sensor and it will unload but won't work right. As soon as I plug one of the sensors (both unit in pump and old unit in hand) it loads down. I'm going to check pump control and unload relays behind the seat and clean the harness plug into the cab tomorrow. I will also check voltages at the sensors but with no specs will just see if they are at least getting power. Unplugging the angle sensor had some effect but nothing like the pressure sensor does. The new is a Chinese made and from reading on here, what are the chances of getting a faulty new sensor?
One more try; I went up and did some more testing. I cleaned the main plug in the cab with no change, then tapped into the pressure sensor plug. The power in was reading 5 volts as it should. With it running, I could get it to completely unload by jumpering the power in and center wires together. I then jumpered in a rheostat and with it could vary the pump output from full unload at 4.8 volts to near load at 2.2 volts and full load with it unplugged and boom function varied accordingly. With this information, I am seeing that the system is working as it should but the sensor is at fault. I am hesitant to say the new sensor I bought is faulty but that is what I am thinking now. My only test would be to build something I could pressurize with a port-a-power and check voltage at different pressures.
Well as it happens we have one doing similar things. But our PVC had blown the power supply resistor. It had no light on, engine controller was just fine. If your lights are on then the computers are likely ok. I found the swing brake solenoid was drawing current to the point of overload, and the operator just put in whatever fuse he could find and blew the PVC. My son fixed the computer but we have a new problem where it is doing the same hydraulic loading, heating the oil and engine. The resistor went again but Son thinks it was faulty, Put in a large one for testing as I bought a new chines PVC off ebay, it functioned for a while and then shut itself down, no light or action, let it cool and it started working again. I called it quits so as not to damage the new unit and put the old back in, I have OHM tested every part and harness , everything checks out and tomorrow is the day to test run. By chance does ANYONE have the correct era John Deere test equipment that plugs into the diagnostic connector??? Our local dealer says its too old for them to work on. They dont have the tester anymore, or so they say This is a great machine exceot for this. I will be testing the pressure sensor as well.
I replaced the pressure sensor with an OEM Japanese made unit with no improvement but unexplainable other problems. I could completely disconnect all sensors to the pump and with no change, or have it function slow then begin loading down by itself, unplug the angle sensor and it would unload. Nothing made sense. I finally said to hell with it and began running it to see what would happen and the blasted thing went back to operating normally for the next 3 hours to shutdown. I'll see what it does again tomorrow. The way it acts its as though it is going into the heat cycle for cold weather... it hisses loudly at the control valve and loads the engine to the point it nearly wouldn't rev up. First testing I could jumper the pressure sensor feed wire into the return and unload it but that quit working also prior to force running it. Regarding the DR ZX tester, there are some on ebay but I haven't read anything good about them. See the post regarding 'slow hydraulics on Hitachi, slow hydraulics'. If the problem comes back, I'll have to call a local yellow JD dealer and see what they can do as I'm out of ideas and can't make heads or tails of what it was doing.
Our dealer wont even touch it unless we are willing to have them throw parts at it, I can do that.lol
Yikes. Mine started out on high pressure this morning (90 F) and stayed on for about half an hour then went to normal. After an incident this last winter where I started it at 20F or so and it went to high idle and I think loaded, I believe it is going into a warmup cycle when it shouldn't. I'm going to keep running it and see if it will fully go away.
Is it high pressure or is the pump going to full swash (loading the engine) It could be one of the pump displacement solenoids on the top of the pump.Switch them and see if the problem is that the pump doesn't pump. Then it is the PDS .
Changed both PDS, did a COMPLETE PVC wire harness check , we got an arm sensor code from the comp. So havent had time to install the sensor yet but the bottom of it was missing a little piece. And they were the old design. Also ohm and putput checked every part on the PVC system and all checks out good so keeping fingers crossed.
So is it working ok again?
So our new china pressure sensor came in and it is working great after install, and ours was doing the full swash. The system defaults to full when the electronics go bad and the controller will keep trying to destroke the solenoids on pump till computer gets hot and blows a fuse or shuts down.
So our saga continues, we got 3 solid weeks of work out of it with No issues, then it went into full swash. Swapped out displacement solenoids, put in new deere switches, nothing helped. Rechecked wiring, the ONLY thing we have not messed with is the proportional control valve. Any input from the experts on this.?? mg2361?? Help.
Recheck the harness. Also try a wiggle test (grab all the harnesses and shake them).Sounds like you have a bad connection somewhere. It may also be a stuck swashplate.On that machine you have two pumps but one swashplate.Sometimes with a little system contamination they will get stuck.Try tapping the pump cover with a hammer. I have taken those pumps apart in the field and found a bad surface where the swash slides on the pump outlet .Sometimes they stick.
This should help all of you with JD "E" excavators (Both attachments). As far a the resistor getting blown, the only thing I have seen there is guys placing a higher amp fuse in place of the F7 1 amp fuse that blows and that will result in the death of he PVC (see Fuse attachment). The attachment will explain why and offer diagnostic tips.
I had similar issues on my Hitachi Ex200-2 a number of years ago, computer was dead and even with a new one it wouldn’t work. The only way to fix it was to rewire the whole machine. I was able to buy the complete wiring harness and install it in about 2 days. Machine has been perfect ever since.