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Hitachi 120-3 Hydraulic / Electronic problems

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tommurphy73

Member
Joined
Dec 1, 2017
Messages
16
Location
Ireland
Hi,
I have a Hitachi 120-3 excavator which has hydraulic / electronic problems. The machine has very slow hydraulics including the track motors. It operates a little like the excavator in this video

I have been trying to diagnose the problem over the last few days and the following is what I know or have found from searching the internet.

It seems that there are 4 sensors controlling the whole machine.
- angle sensor
- engine speed sensor
- DP sensor
- Outlet pump pressure sensor

There are two solenoid valves on top of the pump and these activate the squash plate. One activates and one deactivates.

When the wires are switched on these two solenoid valves the hydraulics works a bit better but not fully right. The Dipper arm is still running slow and if you use a function like the bucket the dipper speeds up and works normally.

Does anyone have any ideas what may be at fault or does anyone have a wiring and hydraulic drawing for this machine.

Any help would be appreciated.

Regards
Tom
 
Last edited:
R

Ronsii

Senior Member
Joined
Jun 26, 2011
Messages
3,464
Location
Western Washington
Occupation
s/e Heavy equipment operator
Have you checked/changed filters? Are both the computers 'heartbeat' LED's flashing normally? Any other history of the machine would also help to diagnose problems.

There are a few threads on this forum that cover troubleshooting of this machine in detail... here is one --> https://www.heavyequipmentforums.com/threads/hitachi-ex120-problem.13447/

there are plenty more, I think that one has a pdf manual link in it somewhere for a SIMILAR machine most of the tech stuff is the same however....
 
T

tommurphy73

Member
Joined
Dec 1, 2017
Messages
16
Location
Ireland
Hi, some further debug has shown that there is a problem with the alternator as the voltage at the battery when charging is around 36V. Max 28V is what I would be expecting. The heartbeat LEDs on the ECUs look to be OK. The other thing I found is if I rotate the angle sensor on the pump while the machine is running the hydraulics will start working normally so it looks like it may be related to this.
 
T

tommurphy73

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Dec 1, 2017
Messages
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Location
Ireland
The filters are OK, There is not too much history except that the machine was purchased with the problem. Initial debug found that the wiring on the pump solenoids had been reversed so the pump was in full squash all the time. To clarify what I said previously, I removed the angle sensor from the pump and if I manually rotate the sensor while still wired in, I can get the pump to go into full squash / pump at full pressure
 
007

007

Senior Member
Joined
Dec 28, 2016
Messages
282
Location
Australia
a lot of that style of electronic sensors only have 33V max supply voltage so maybe you should fix your alt and then see whats not working?
older style alternators have a fixed control voltage of approx 28.4 but the more modern is being temp compensated and also different voltage to suit the new calcium battery's so the voltage can be quit different between machines but no more than 29.6.
 
T

tommurphy73

Member
Joined
Dec 1, 2017
Messages
16
Location
Ireland
While we are waiting for a replacement alternator we will try running the machine with the alternator disconnected. Hopefully it will behave itself a little better then. Going to be the weekend before we can look at it.
 
007

007

Senior Member
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Dec 28, 2016
Messages
282
Location
Australia
Hi Tom,
Just a word of warning if you remove all the wires from the alternator it may catch on fire with no connection to the battery.
If you leave the main output wire on and remove the small wires that should stop it exciting and just spin ok.
 
T

tommurphy73

Member
Joined
Dec 1, 2017
Messages
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Location
Ireland
Thanks for the word of warning, I will keep that in mind. I think it is safer to replace the alternator before doing anything.
 
L

lawrielzee

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Joined
Dec 14, 2017
Messages
8
Location
Phillippines
  • Good day this are the effect of those sensors if they are faulty.
  1. Angle sensor the pump will not angle or it will go to neutral, engine will not be affected and it will still accelerate.
  2. Differential pressure sensor the pump will go to full angle and the engine will be affected acceleration will be gone and the engine will smoke as it will have full pump load, it will stall if you try to move the control lever.
  3. N Sensor or engine speed sensor the relay that send positive voltage to the two solenoid valves on the pump will not turn on as the ecu detect that your engine is not running making the effect same as number 2.
  4. P Sensor or output pressure sensor you could still operate your machine normally, engine acceleration normal pump pressure normal but will lack power when digging or excavating.
  5. PVC or pump variable controller sometimes even if the led indicator beat normal the output transistor is damage making the pump ecu defective look for those 4 transistor inside and visually inspect for sign of damage or use multimeter to check it.
  6. The 2 pump solenoid valve, check the winding for continuity and also check the valves if it is open blow air to one of valves holes if the air goes to the other hole it is stuck open.
 
T

tommurphy73

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Dec 1, 2017
Messages
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Location
Ireland
Thanks for all the updates so far.

Update on the Hydraulic problems:

The alternator replaced and the voltage is now back to normal 29 volts when charging.

I then re-fitted the angle sensor. When fitting and setting up the angle sensor I first had it at 4.3 volts output on the pump while the pump is at full stroke. The machine started but had very very slow movement and constant power to the pump solinoid nearest to the door which means the pump is not in stroke.

Readjusted the angle sensor looking for 4.4 volts but this time it was set 4.5 volts. I got constant power to the inside pump solenoid which means the pump was staying in full stroke and engine was under pressure but Hydraulics were moving fast.

I will get back at it again at the weekend and set the angle sensor to 4.4 volts but does 0.1 volts above or below 4.4V make that much difference?

From the previous response from Lawrielzee, it may be the differential pressure sensor or the N Sensor that is now at fault?

Regards
Tom
 
K

Knivens894

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Oct 16, 2014
Messages
115
Location
Black Creek, GA
The DP sensor on the main spool block controls the rate of response of the hydraulic system. Normal setting is 1.1 V but it may be adjusted up to 1.4 V (per specs) to slow down system response to control inputs.
 
Tones

Tones

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Tom, your 1 post has a video of a slow working Hitachi. This bloke has posted other videos were they removed the computer and got the machine working pretty darn good. It just may save doing your head in and your wallet.
 
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tommurphy73

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Dec 1, 2017
Messages
16
Location
Ireland
I forgot to update this thread with the status of the Hitachi Excavator.

Good news is it is working perfectly now. After fixing the alternator it was found that there were two remaining faults.

There was a bad wire on the DP sensor which caused the pump to go into full squash all the time. The second fault was the Dipper arm was slow caused by the proportional valve. The spool had threaded apart inside the proportional valve so that is could not travel back and forward.

Due to the success of the first machine I was asked to have a look at a second Hitachi Excavator which had a similar hydraulic problem. However on inspection the problem appears to be quite different. The symptoms are as follows

1. THe pump goes in and out of squash but as soon as there is any load it comes out of squash and cannot dig
2. Checked the angle sensor and it looks OK
3. The DP sensor was checked and seems OK
4. The pump is OK as it works perfectly when both solenoids on top of the pump are disconnected so that it goes into full squash.

Regards
Tom
 
R

RedMcC

Member
Joined
Jul 31, 2015
Messages
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Location
Canberra, Australia
Hi
tommurphy73 said:
I forgot to update this thread with the status of the Hitachi Excavator.

Good news is it is working perfectly now. After fixing the alternator it was found that there were two remaining faults.

There was a bad wire on the DP sensor which caused the pump to go into full squash all the time. The second fault was the Dipper arm was slow caused by the proportional valve. The spool had threaded apart inside the proportional valve so that is could not travel back and forward.

Due to the success of the first machine I was asked to have a look at a second Hitachi Excavator which had a similar hydraulic problem. However on inspection the problem appears to be quite different. The symptoms are as follows

1. THe pump goes in and out of squash but as soon as there is any load it comes out of squash and cannot dig
2. Checked the angle sensor and it looks OK
3. The DP sensor was checked and seems OK
4. The pump is OK as it works perfectly when both solenoids on top of the pump are disconnected so that it goes into full squash.

Regards
Tom
Click to expand...

Were you getting any "hiss" that sounded like a pressure relief valve? (I've got a machine with some related symptoms...)
 
F

fatloser

Member
Joined
Apr 17, 2013
Messages
10
Location
usa
I have 24volts at my pump control solenoids at all times. Also 24volts at travel speed solenoid. Any ideas? I have been struggling figuring out my problem Thank you for any help
 
JDirt

JDirt

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Jun 16, 2017
Messages
83
Location
Competition, MO
The pump control solenoid are supposed to have constant 24v. The computer activates them by grounding the ground wire. You have to rig up a light in between the plugs to see if the solenoid is getting a signal to activate.
 
L

lawrielzee

Member
Joined
Dec 14, 2017
Messages
8
Location
Phillippines
tommurphy73 said:
I forgot to update this thread with the status of the Hitachi Excavator.

Good news is it is working perfectly now. After fixing the alternator it was found that there were two remaining faults.

There was a bad wire on the DP sensor which caused the pump to go into full squash all the time. The second fault was the Dipper arm was slow caused by the proportional valve. The spool had threaded apart inside the proportional valve so that is could not travel back and forward.

Due to the success of the first machine I was asked to have a look at a second Hitachi Excavator which had a similar hydraulic problem. However on inspection the problem appears to be quite different. The symptoms are as follows

1. THe pump goes in and out of squash but as soon as there is any load it comes out of squash and cannot dig
2. Checked the angle sensor and it looks OK
3. The DP sensor was checked and seems OK
4. The pump is OK as it works perfectly when both solenoids on top of the pump are disconnected so that it goes into full squash.

Regards
Tom
Click to expand...
There are possible cause, first the p sensor (electrical) and second the main relief valve (mechanical) it may also be cause by the main control valve (ex. O-ring, and spool stuck)
 
L

lawrielzee

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Joined
Dec 14, 2017
Messages
8
Location
Phillippines
fatloser said:
I have 24volts at my pump control solenoids at all times. Also 24volts at travel speed solenoid. Any ideas? I have been struggling figuring out my problem Thank you for any help
Click to expand...
You should only have 24 volts at travel speed solenoid when you are in rabbit mode, when measuring always measure the two wire connected in solenoid, positive is always present as ground is controlled by the ecu.
 
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