Komatsu PC78US-6 Low Power/Stalling

[lmcnei3]

Evening members,


I've been reading some threads on here and it seems to be a common issue with these machines.
Little background;

Machine Serial # 9319


I bought this machine knowing it wasn't running properly. It would run for a bit, and had slow functions. Mainly tracking and curling the bucket in are the slowest/weakest. When I'm digging a hole it won't curl the bucket while it is in the ground which should be the strongest function. After doing multiple functions for a while the machine would eventually stall out. The engine runs strong, and doesn't blow out a cloud of smoke at all except for startup. I can operator the boom and bucket in digging motions in the air for about a minute before the machine stalls out. Starts right back up immediately. It never smokes when it stalls out. At first I thought it was a fuel problem, so I completely cleaned out the tank, put new diesel, replaced the filters, blew the lines back from the fuel water separator back into the tank, and from the fuel water separator back to the supply pump. No restrictions either way, fuel flows out like a faucet. I pulled off the banjo fitting on the supply of the fuel pump at the hand primer on the injector pump, and the screen is clean. So maybe the fuel supply pump is bad? well, i replaced that today. Didn't change a lick how it was running. There is one more screen on a banjo bolt directly on the injection pump, pulled that off and it was clean as could be. The filters didn't have any crud or residue in them.

I feel I've ruled out fuel as being the problem, it seems to be something hydraulic is overriding the engine. Next step i plan on doing is pulling the hydraulic filter off and checking out that system and clean it completely. I want to pull out the control valves and see if anything is gummed up.

I haven't checked the pressure on anything as of yet, these hydraulic systems are pretty new to me. That's going to be next, next. People tell me to sell this machine. I'm too hard headed for that.


Any tips or pointers would be appreciated, thanks guys.

 

[uffex]

Good day
Attached some Komatsu info may be helpful.
Kind regards
Uffex

 

[John C.]

I ran the serial number of your machine through my materials and it doesn't show up. That usually means it is gray market. I'm guessing at the year being around 2005 or 2006. Do you know if the engine is a genuine Komatsu or a Cummins clone? The machines in that Dash series had lots of issues and lots of changes in the pumps and main control valves. Killing the engine with no extra smoke generally indicates a fuel problem and I would guess by what you say you have already done, that I would be looking at pulling that injection pump off and have it gone through. The other key piece of information that you haven't stated is how many hours are on this machine?

 

[lmcnei3]

The machine was purchased from H&E in Baton Rouge, LA in 2006. It currently has 5300 hours, and the pretty sure the engine is a genuine Komatsu. Would it benefit me to TEE off each hard line with a gauge coming out of the injection pump into the engine?

 

[John C.]

Have you checked for fault codes on the monitor panel? Does your engine have a common rail injection system or a mechanical pump with individual injector lines.

 

[lmcnei3]

It has a mechanical pump with individual injector lines.


On the fault codes; I'll have to get back to you on that once i figure out how to pull it up on the monitor panel

 

[NWH]

I had a similar problems with my 08 pc78us-6. It turned to be the pump swash plate sticking. This is aknown problem with these machines .

 

[lmcnei3]

I had a similar problems with my 08 pc78us-6. It turned to be the pump swash plate sticking. This is aknown problem with these machines .

You had to replace the whole hydraulic pump didn't you?

If I could just replace the swash plate that would be preferable, and get some use out of this thing

 

[lmcnei3]

Pulled up the error codes

now if it doesn’t have an E underneath it that means the codes are old and dealt with correct?

here is what I found

 

[John C.]

Code 304 is short circuit or ground fault in engine stop circuit solenoid relay system
Code 233 is disconnection in TVC-EPC solenoid system
Code 213 is disconnection in swing holding brake solenoid system.
You are correct about the E not being displayed indicates the codes are not currently active.
I haven't heard of a swash plate sticking issue on those machines but like I said above, there were lots of problems on the Dash 6 line for quite awhile. As I recall the swash plate sits in a cradle that is part of the pump housing. If it is sticking, I believe that it would kill the engine when you let off a function as the flow in the pump would not change but the opening on the valve would be closing up and now there is nowhere for the oil to go except over the main relief.

Interesting problem. Let us know what you find.

 

[lmcnei3]

After doing more digging, I had two active codes pop up on the machine 233, and 213

then the machine stalled out again.


Also managed to pull up one of the computer screens that showed fluctuations in my pressure. Let me try to upload that one.

 

[lmcnei3]

Can’t seem to upload videos

this was on my monitor before the machine shut down

 

[Bn127953]

I am experiencing the exact same issue with my 2007 Pc78 with 8600 hours. What was the solution to your problem?

 

[Evan Mutchler]

Have you come up with a solution? I have an '04 machine doing the same as both of y'all. I haven't had time to pull codes yet, have you checked the wiring harness to the pump controls? Trying to get an idea of where to jump in on troubleshooting

 

[Hunter91]

I have an 08 pc88 mr-6 with similar issues. Hydraulics are OK but a bit slow and weak when cold but as she heats up. Multiple functions and heavy loads will will bog the engine and stall if I dont stop the function quick enough. Can anyone tell me how to use the dash to pull fault codes? Same control panel as the pictures above.

 

[lmcnei3]

Had a komatsu Tech hook up gauges to my pump, and turns out my pump isn’t destroking. So I Brought the pump to a local shop to get rebuilt, which should be finished soon. This shop has a good reputation, so I’m hoping he can get it taken care of.. because komatsu wanted $12,000 for one of their Reman pump.

 

[lmcnei3]

Got the rebuilt pump in my machine, and pressure is reading what it should be/within spec. The engine doesn't bog down anymore. BUT, it still has slow compound function of boom up and arm in. I pulled the main boom cylinder and all seals were good, without any scarring or marks on the rod or barrel. After hooking gauges up to the main valve body, the book is stating the compensating valve is bad. we pulled it out for inspection, and it is scarred. Now we are going to pull the control valve and inspect it for debris and damage. THE NEVERENDING PROJECT CONTINUES.