Hitachi ex120-2 intermittent slow hydraulics for all functions.

[Diesel Dave]

I looked up that part number and it sends me to one that Friday parts sells. I’ve looked at that sensor and in the application section it doesn’t specifically list an ex120-2. Does anybody know if that is still the correct part for my machine??

Per post # 16, the P sensor part # I quoted is 100% accurate for an EX120-2 .
The (2) original Hitachi part # ‘s subbed to # 4436271 .

 

[Newberryi]

I checked that I have more than 4.75 volts but that’s just reference voltage right? Couldn’t I have reference voltage and still get a false output reading if the sensor is bad internally? Sorry for so many questions just trying to fully understand what and how it works. Is rhe pressure sensor just and on or off type sensor or is it a sensor that gives various readings depending on what is input to it?

 

[Newberryi]

Thanks for the info diesel Dave I’ll get one coming from Friday parts

 

[Diesel Dave]

I checked that I have more than 4.75 volts but that’s just reference voltage right? Couldn’t I have reference voltage and still get a false output reading if the sensor is bad internally? Sorry for so many questions just trying to fully understand what and how it works. Is rhe pressure sensor just and on or off type sensor or is it a sensor that gives various readings depending on what is input to it?

Of the 3 sensor wires ,the one in the middle position is the signal wire back to the PVC. Under normal conditions the signal voltage back to the PVC varies between .26 V and 4.74 V depending on the hydraulic pump pressure.
What @ Shopguy is suggesting is to back probe the middle wire with key on engine not running.

 

[Newberryi]

Should it be low voltage with key on engine off or is it just good if it’s under 4.75?

 

[Newberryi]

Key on engine off we have .04 volts on p sensor middle wire

 

[Diesel Dave]

Should it be low voltage with key on engine off or is it just good if it’s under 4.75?

I want to say low voltage , something above .26V

Key on engine off we have .04 volts on p sensor middle wire

You are back probing the middle wire with the harness connected to the sensor ?
With that low of a voltage , fault code # 28 should be produced.

 

[Newberryi]

Yes middle wire is only .04v

 

[Diesel Dave]

Yes middle wire is only .04v

Per the manual , Fault code 28 indicates that the sensing signal (input
voltage of the sensor) is lower than 0.25V, and pos-
sible cause may be disconnection of the harness be-
tween the P sensor and the PVC.

 

[shopguy]

Stall a cylinder and see what the voltage is also I would try another volt meter 1/4 volt ain’t much

 

[Newberryi]

Had some time to mess with machine again today. Replaced the pressure sensor and everything seems to be working well except the curl on the bucket. We removed the solenoid/valve made sure is didn’t look clogged and reinstalled. Manual says it should ohm out between 5 ane 23.2 ohm. Our solenoid reads 23.9 but so does the one above which seems to be fine so I don’t know where to go from here. There is no more codes for pressure switch but when I re checked codes it looks like I have a code 14 but I don’t see a code 14 in the manual. Help please!

 

[Diesel Dave]

Had some time to mess with machine again today. Replaced the pressure sensor and everything seems to be working well except the curl on the bucket. We removed the solenoid/valve made sure is didn’t look clogged and reinstalled. Manual says it should ohm out between 5 ane 23.2 ohm. Our solenoid reads 23.9 but so does the one above which seems to be fine so I don’t know where to go from here. There is no more codes for pressure switch but when I re checked codes it looks like I have a code 14 but I don’t see a code 14 in the manual. Help please!

What issue are you having with the bucket curl ?
What solenoid valve did you remove and check ?
I don’t see a code 14 listed in the EX120-2 or EX120-3 manual.

 

[Newberryi]

the bucket curl was so slow. Prob 10-15 seconds to only use half the range of the cylinder. So we unplugged the solenoid valve and and started machine and it’s curling normal speed now. It’s the solenoid that works the bucket curl for the pilot circuit I’m pretty sure. That block area has spots for 8 solenoid valves and on the engine side has two relief valve looking things.

 

[Newberryi]

After running the machine with that solenoid unplugged for 20 minutes or so the hydraulics for the tracks would get slow but you could get them back if you messed with the boom functions and vice versa. If you grab the pilot lines where the pilot filter is located back by the main pump, it’s like the line is hammering or pulsing when you are using any function. Seems to be a sharp hard pulse almost like it’s loosing pilot pressure in the line for a split second then slamming all the line pressure back.

 

[Newberryi]

I do not know if the pilot lines were pulsing before today I didn’t grab the lines while it was running until after we unplugged solenoid

 

[Diesel Dave]

After running the machine with that solenoid unplugged for 20 minutes or so the hydraulics for the tracks would get slow but you could get them back if you messed with the boom functions and vice versa. If you grab the pilot lines where the pilot filter is located back by the main pump, it’s like the line is hammering or pulsing when you are using any function. Seems to be a sharp hard pulse almost like it’s loosing pilot pressure in the line for a split second then slamming all the line pressure back.

I want to say the pulsing in the pilot line is normal. The pulsing is created by the (2) displacement solenoid valves (on the top of the hydraulic pump) being cycled on and off by the PVC to maintain a constant pump flow while you using a function.

 

[Diesel Dave]

@Newberryi, did you ever end up being able to get the pump displacement angle sensor adjusted to the 4.4 volts ?

 

[Newberryi]

No sir, the best I got was 2v with the original and the new angle sensor. I really don’t understand the system good enough to know what would be the effect of have an angle sensor that was only set to 2v? Would that tell the pump to pump more or less or does is tell the EC to tell some other sensor information? I’m kind of at a loss. I don’t understand why unplugging the solenoid for the bucket curl sped the curl up and I don’t understand how you can get track speed to get back to normal when operating the boom functions when it’s acting up. Any help or direction would be so much appreciated

 

[Diesel Dave]

No sir, the best I got was 2v with the original and the new angle sensor. I really don’t understand the system good enough to know what would be the effect of have an angle sensor that was only set to 2v? Would that tell the pump to pump more or less or does is tell the EC to tell some other sensor information? I’m kind of at a loss. I don’t understand why unplugging the solenoid for the bucket curl sped the curl up and I don’t understand how you can get track speed to get back to normal when operating the boom functions when it’s acting up. Any help or direction would be so much appreciated

You tried adjusting the angle sensor exactly as per the manual ?
The small spring clip between the pump and the sensor is in place ?
Are you able to achieve 4.4 V if you turn the angle sensor shaft by hand ?
If all above is ok, maybe someone has limited the maximum pump swash angle by performing the electronic control bypass procedure. The procedure is from a Deere 490E operators manual but does apply to an EX120-2 as well.
.

 

[Newberryi]

Definitely wasn’t aware of a procedure like that so it’s possible but what does that procedure do to the functionality of the pump? Seems like the machine is working properly most of the time but intermittent slow functions but can get them back if you mess with multiple functions simultaneously. If you put it in the locked position does it hold the pump at a specific angle and keep it there?