Komatsu PC21O-8 slow in B mode

[rockfall]

Hey guys,

My PC210-8 was working great all of a sudden it became slow in B mode. The boom, one track and the arm curl was very slow. I checked the pressure switches on the junction box and all the pressure switches were damaged along with the hydraulic sensors behind the control valve for F and R pump. I replaced all the three pin switches which are 6 and the rest two are two pin (Red color) which I did not change because they were working. Also didnt change the pressure switches behind the control. The excavator worked great for a week and now the machine has low power in B mode. Replaced all the 3 solenoids on the pump and 2 on the merge-divider valve. Checked the LS valves on the pump that looked great. In addition, I changed the self reducing valve for pilot pressure but no difference. Any clues what I can do next.

Thanks

 

[rockfall]

Anybody there??

 

[mikebramel]

The malfunction is only in one mode, you are sure of this

 

[rockfall]

Yes. I think its because B mode is lowest among all other modes. I have also noticed another thing. The pressure sensor for F pump reads 426 at low idle and doesnt change at high idle which the other pump reads 35 at low idle.

Looks like the pump is leaking pressure internally or the merge-divider is malfunctioning both of which is leading to power loss

 

[Hydraumind]

Can you please specify the unit of the pressure reading: PSI? bar?

 

[rockfall]

Its kg/cm2

 

[John C.]

So the problem only exists in one mode of operation. That seems to rule out any problem with the pump itself. Next issue could be the computer has a problem that only exists in that mode. Are you getting your pressure readings from the monitor panel or have you plumbed in gauges to check the pressures? You mention those pressure switches were damaged along with the pressure sensors. What kind of damage are you talking about and what caused the damage? You don't mention any fault codes but if there was damage on any of those electrical components there would have been a bunch of fault codes. Are they still there or did you clear them out of the computer?

 

[rockfall]

Hi John,
By damaged I mean it stopped working. The accelerator was not kickin with 6 functions that had a 3 pin black color sensor for it. Accelerator was kickin for two functions only which is lowering boom and extending stick which had red color sensor. Those were working. Dont know but the technician said that all six sensors had a common wire which was touching and damaged them.
I also tried to work on cuttinh off the computer but still the same. The readings are there on the monitor screen and I also plumbed gauges which was showing 350 bars.

 

[John C.]

Sounds like you have more problems than you know right now. I would suggest you start by listing all the fault codes on the monitor panel. Do you know how to pull them up?

 

[rockfall]

Hi John,
I had the merge-divider valve taken out and noticed a spool stuck. The equipment is working gr8 as far as hydraulics are concerned. Hope I dont get electric issues later. Thanks a lot!

I will post a new thread about my other PC220-7 excavator. Need your input on that.

 

[rockfall]

Hi John,

The machine worked fine for 3 days. Now again it started acting up. The accelerator doesnt kick in bucket curl, arm curl etc.. . Why is this happening again and again? Is the computer faulty or what or is there a short circuit? I have seen some PC210-8 machines with the solenoids on the pump reading on the screen is more than 900 Ma (Milli Ampere). My solenoids doesnt go above 750 Ma. Why is that though. Does this low Ma has to do something with the computer being faulty and not energizing the solenoids properly?

One more thing. What is the function of the two oil pressure switches on the merge-divider valve and overload sensor located on a block between the two boom cylinders? Is it only for displaying pressure on the screen or it plays a role in speeding up lever functions and de=stroking or up-stroking the pump?

There are lots of codes:

 

[John C.]

It is sounding more like a wiring issue. Pressure switches are usually used to tell the computer that something is being used. They are usually just on and off type switches that are normally open and close when a specified amount of pressure is applied. Possibly when the machine was last worked on a harness was moved around and the short circuit stopped until after working for a time the harness settled back into the position that allowed the problem again.

I'll have to do some studying on the pressure switches. I've never heard of an overload sensor on a Komatsu excavator before. I haven't had to fix a Dash 8 so maybe it is something new to me.

 

[John C.]

For some reason I didn't see the photos when I answered your post. I see the machine shows 17,000 plus hours on the display. All those codes are symptoms of a bad wiring harness. I have seen those harnesses short through inside the outer covers. I seems oil and heat over time degrades the insulation on the wires. I used to use an ohm meter to check for continuity between the wires looking for shorts. You also need to check your grounds. I have had a few high hour machines get corrosion on connections and not make ground anymore.

 

[rockfall]

Hey john,

Problem fixed. Replaced all three solenoids, one LS valve was stuck had it polished a little bit and for some reason the two pilot hoses from pump to control valve were swapped and had it swapped to its original location on the pump.
Thanks for your input