Komatsu pc490-10 slow boom up

[tbone1471]

We have a pc490-10 and occasionally the boom will raise slow. Some other function like stick out and slew seem to also be slow. It is very random.

What we are seeing is the rear pump not increase displacement. It sits at 24cc while the front pump will go to 206cc. When the boom functions normally both stroke to 206.

Both pumps will deliver the same pressure. Pcc boom up pressure is 380psi when both fast and slow.

I have attached screenshots of what the computer is seeing when it is acting slow. Is there a valve that could be randomly hanging that would cause the rear pump to not increase displacement but would still allow it to build pressure?

Machine has 7000 hours and has been trouble free up until now. We did a hydraulic service recently and there were no contaminants. Issue had come up prior to the service. The main reason for the service was a leaky return to tank line.

Looking for some insight as komatsu doesn’t seem to have any techs readily available.

 

[funwithfuel]

Well you might want to check your manual. I think your pilot oil is too low. Should be closer to 500psi iirc. If there's no sense of demand, then the rear pump is unlikely to give full flow. Are you working in P mode or E or L?

 

[tbone1471]

This is in p mode. I also thought this was on the low side but I am more familiar with Deere where they run around 550.

What led me away from pilot pressure issues was it functioning normally with the same amount of pilot pressure.

I should have noted it will do this more often with a full bucket but will also do it with an empty bucket.

 

[funwithfuel]

I will look up specs in AM . That is if Lachou doesn't beat me to it. Did you notice if merge/divide solenoid was energized?

 

[tbone1471]

I did not. Does it have a specific callout in the menu or does it need to be checked on the control valve? I’m unsure of the location..

 

[funwithfuel]

Its in monitoring, pre-selected

 

[tbone1471]

I will check in the am. Thanks for your help.

 

[funwithfuel]

Please see attached

 

[LACHAU]

@tbone1471:
You should check 02 items 08000 (Merge-divide Sol Current Main) and 08001 (Merge-divide Sol Current LS) to see what their values are.

If their values are correct, then I would say that you should disassemble the Merge-Divider valve to check, most likely this valve is stuck

 

[aareeyesee]

Sorry to revive a sorta dead post but I have a pc490 that is slow on all functions. The pump isn't stroking and I've checked most of the things in the merge and ls circuits. It's there an way to see if the pump controller is causing this? Is the pump controller a regular failure? I'm a cat field tech and I've been "gifted" this pc490-11 cause it moves too slow to get it far enough away from me.

 

[tbone1471]

We never fixed ours. Komatsu came out and has suggested we replace the quick dump valve for the stick circuit on the control valve.
Parts showed up but no time to sort it out.

They recommended this replacement because they were seeing pilot pressure on both sides of the stick pilot . I.e. when stick in on control we would have a few psi on the pilot for stick extend. Almost like they are fighting each other.

 

[funwithfuel]

We never fixed ours. Komatsu came out and has suggested we replace the quick dump valve for the stick circuit on the control valve.
Parts showed up but no time to sort it out.

They recommended this replacement because they were seeing pilot pressure on both sides of the stick pilot . I.e. when stick in on control we would have a few psi on the pilot for stick extend. Almost like they are fighting each other.

I apologize for not asking sooner, does your machine have a pattern change valve? If those things aren't all the way one side or the other, you get all kinds of issues with boom and stick. This applies to you as well tbone, check for a pattern change and make sure it's all the way in ISO or backhoe. No in between.

 

[tbone1471]

We checked ours and the initial issue followed the sticks ruling out the pattern valve.

I am supposed to be on that job site tomorrow and if everything works out I am going to put the quick dump valve on.

 

[funwithfuel]

Not seeing how quick dump is gonna put pilot oil on the other side of the spool. I think I'd be gauging pilot oil at the RCVs. They are monitored, you could observe in the service screen.

 

[aareeyesee]

After tearing this control valve all to hell and checking all sorts of electrical stuff, if the damned pattern change fixes it I'm gonna have to write one hell of a story. And drink quite a bit.

 

[aareeyesee]

Well it isn't the pattern valve. I did find that the pmf and pmr pressures are 150psi at low idle and 150psi high idle. Spec is 300/150 tore apart the can behind the main control valve, saw nothing unusual.

 

[funwithfuel]

What kind of pilot pressure do you have, At the spool caps?

 

[aareeyesee]

the bucket dig pilot is 175-200psi at the spool and I put a gauge on the #10 epc valve posted on the pic lachau posted above and no pressure ever came to that solenoid no matter what I moved.

 

[aareeyesee]

Well I knew this was going to end up being weird. I pulled off the pressure reducing valve block and pulled everything out of it. One of the valves has a sharp little pin in it. I took some scotchbrite and cleaned up a wear ring on the pin and stretched the spring out and now it works fine. Everything else in there looked ok other than the pin and seat. I'll order one of those and replace it later, but at the moment its running fine.