Komatsu pc200-5 slow operation after hammer hooked up.

[John C.]

You are correct about the computer modulation. You can check the solenoid by removing it and checking the plugger. Turn the key on and hold your finger over the plunger on the end of the solenoid. You should feel it move in and out as you shift the mode switch on the monitor panel. The other thing you can do is reinstall the solenoid and disconnect the harness connector and then operate the machine. The pump should be able to overload the engine in that case. You can check the pressure coming out of the solenoid as well. You can also check TVC pressure. If you look at the center of the pump and in between the two control blocks on the pump, you will see an eleven sixteenths bolt head. That is the passage for checking the TVC pressure. With the engine at high idle, mode in HO and power in H and the controls in neutral, the pressure should be somewhere around 360 PSI. With two pumps running with a control dead headed over relief, you should see somewhere around 270 PSI.

 

[davecampbell]

You can also check TVC pressure. If you look at the center of the pump and in between the two control blocks on the pump, you will see an eleven sixteenths bolt head. That is the passage for checking the TVC pressure.

I tried the overide switch, no difference. I went out and cut the wire to tvc solenoid (the plug has been eliminated), still no difference and no load on motor. So I pulled the solenoid and touched the wires to 24 volt and it pushes out. It doesnt retract, but with power removed I pushes back in smoothly. I tried pushing down in the center of the hole I removed it from to see if I could feel the spring it moved against, but I felt no movement. Maybe it opposes hydraulic pressure? I looked in vain for the 11/16 test port. Could not find it on my 150 either. The only 11/16 head I could find looked like an adjustment of some sort on the bottom of each control block. There is a hard line between the two control blocks. Could that be carrying tvc pressure between the two blocks?

 

[John C.]

As I recall the fitting is on the side of one of the control blocks. The lifting eye in the photo is the center of the pump. As I recall, the fitting will be on the forward valve block.
The fact that the solenoid moved usually meant there was no problem with it. Judging from the oily dirt all over the pump in your photo and the age of the machine, it is probable the the piston inside the valve block that the TVC solenoid pushes against is stuck in place. The oil that operates all those controls is not filtered directly by the return filter. There are small button looking filters inside the pump that by this time have holes poked through them. It looks to me like you will have to at the least remove the control valve blocks, dismantle, clean them up and reassemble with new seals. Just a guess at this point based on experience.

 

[davecampbell]

I had an old 888 case, it had a shutoff on the suction. I dont see that on this one, do I just need to drain the tank to do this?

 

[John C.]

I would just drain the tank below the level of the pump control valves. If the oil is old, I would just drain it all. I use a barrel pump instead of trying to open the drain plug on the bottom.

 

[davecampbell]

it is probable the the piston inside the valve block that the TVC solenoid pushes against is stuck in place.

laying in bed last night thinking through this. It seems like a stuck piston should make it work slow all the time. Since it works at decent speed for a couple minutes before it slows down it makes me think it is either something plugging up as it runs, or some pressure building somewhere that is giving the pump a false signal to flatten out. I am really confused by the combination of a jet sensor in the valve body that is plumbed back to pump controls and the computer controlled solenoid. Is this pump electrically controlled or hydraulically?

 

[Ronsii]

Go over to insanehydraulics.com and do some reading up on how some of the komatsu tvc pump stuff works.

 

[John C.]

I have reviewed that site and find that the guy really doesn't understand what he is talking about on the Komatsu systems. His explanations will just confuse you.

 

[davecampbell]

Go over to insanehydraulics.com and do some reading up on how some of the komatsu tvc pump stuff works.

I have reviewed that site and find that the guy really doesn't understand what he is talking about on the Komatsu systems. His explanations will just confuse you.

I've been on that site, but I was confused before I got there, so I cant blame my confusion on him. I'm pouring over the hydraulic schematic for my machine and I'm not understanding much of it.

 

[davecampbell]

It could just be a coincidence, but it definately started after I hooked up the hammer. I didnt flush the attachment, but since the return goes straight to the filter it seems like any trash would have to have gone straight there and be picked up by filter. Since the tvc seems to do different settings for different functions, could the hammer control circuit be building pressure somewhere that would send tvc a false signal?

 

[John C.]

It takes time. Focus on the pump controls first. This system uses pilot oil to stroke and destroke the pumps. Pilot oil is provided first to the TVC valve and then the NC valve and finally the Cut Out valve. The TVC valve supplies both pumps, so your observation about the cross over tube is correct. Since both pumps seem to be affected, it would be logical to assume the problem is in the TVC valve block. You can see the actions of the pump control valves by following the dotted lines from those valves back to their origins.

 

[John C.]

The TVC is only controlled by the computer. It is a regulator valve that controls pilot pressure.

 

[davecampbell]

Since I couldnt find the pressure tap for pilot pressure I put it on what I think is a charge pump. Looks like a small gear pump piggybacked onto main pump. I got a little over 500 psi operating cold. Ran the machine until it went into slow mode (about 15 min this time). Still maintained 490 psi. Then I went hunting for the pilot tap again. I believe I found it on the front side of front control block. It isn't even hitting 100lbs with operation. About 60 at idle and drops when motor is pushed to high idle. That seemed strange to me. Then hits about 80 with boom up topped out. I'll try to let it cool off enough to get pilot pressure readings with it operating cold. I'll also try to upload a video of pressure guage on pilot pressure.

 

[davecampbell]

Let I sit for a couple of hours and saw over 200 on pilot pressure. Only lasted about 15 seconds. So now, what can cause loss of pilot pressure?

 

[davecampbell]

 

[John C.]

You have a piston stuck in the TVC valve. Get a hold of a parts breakdown so you can see how it comes apart. You can pull off the end plates to get access to the piston. I believe there is a spring on the opposite side of where the solenoid plugs into and you have to push the piston out. Make sure you note the orientation of the piston when it comes out. I can't recall if it has to be in the right direction or not, but I seem to remember that it does.

 

[davecampbell]

Is it just sticking when it gets warm?

 

[John C.]

It likely has crud in the bore.

 

[davecampbell]

It had been working when I first fired it up, and then slowing down after it ran a bit. This morning I went out and cleaned 100 mesh screen. Then fired it up and it was slow right from get go and pressure never reached 100psi. I was hoping that when i cleaned the screen i was going to get good pressure. I would sure like to be able to tell where on the hydraulic schematic I have my pressure tap at.

 

[davecampbell]