Komatsu PC78 MR6 low power and stalling

[Tags]

Could it be a travel valve hanging up and overloading the hydraulics when you're trying to dig?

 

[TexasDan]

Could it be a travel valve hanging up and overloading the hydraulics when you're trying to dig?

Interesting, but if that was the case wouldn't it be pretty strong while traveling? It seems like it's almost never strong traveling, it will struggle, and occasional stall when tracking up a 1 degree incline. It also will barely counter track. If im going uphill and I want to turn to the left I can't just track forward with the right track, I need to reverse with the left track to use gravity to assist the machine. It'll generally stall if I just track uphill with one track.

 

[John C.]

I’ve been kind of watching this thread from time to time. Were it me I would install a couple of gages and watch what happens when you are traveling the machine.

 

[TexasDan]

I’ve been kind of watching this thread from time to time. Were it me I would install a couple of gages and watch what happens when you are traveling the machine.

I've never personally messed with gauges on the hydraulic circuits, so a couple of dumb questions...

Anything I need to know about disconnecting hydraulic connections?

Do you need to de-pressure the hydraulic system before uncoupling the connections?

Do you need to bleed the system after installing the gauges?

Any particular valves you think would be most important to monitor?

I'll see if I can buy some gauges next time I go to TSC. I should be able to find a hydraulic manifold diagram on the service manual. Sorry for the dumb questions, I'm not as mechanically savvy as most people on this forum.

Thanks for the input though!

 

[thepumpguysc]

Incase u missed it, your injection pump DOES HAVE a hand primer on the supply pump.. it just has a white/clear plastic cover over it..
Remove the cover..and get a rider to pump the hp when it starts to stall and see if it doesn’t catch up..

another thing, I find it hard to believe that it doesn’t have a screen in the banjo bolt below the hp..

I see your inlet at the front of the pump, but do u have a return.??
If so, it’ll b a banjo bolt w a spring and ball in it.. it’s called an OVERFLOW VALVE..
It’s purpose is to hold fuel pressure in the fuel gallery..

If your loosing fuel pressure when u stall or turn it off.. either the overflow valve is bad(if equipped)
OR the valves in the supply pump ate the seats outta the supply pump.. and allowing the fuel to leak back/down.. or the piston in the sp is scored..
U can get a new sp for just about the cost of having a fuel shop to o/h it and there’s no telling if they’ll cut the seats or not.. it’s a crap shoot..
There’s a p# on the supply pump itself..

 

[John C.]

thepumpguysc is spot on. That white plastic accordion piece is covering the hand wheel of the priming pump. The banjo bolt is underneath that component and connects the fuel line from the tank to that pump.

Take a photo of the monitor panel and post it here. There is a good chance that you can watch your travel pressures from the monitor panel. I just need to see what you have.

 

[thepumpguysc]

BTW.. WHERE did u take the fuel pressure reading from.??
I like to take it at the inj. pump INLET.. but on your unit, it looks like there isn’t enough room.??
If it has an overflow valve, u can take it out and push on the ball or shake it to hear if the spring is broken..
Good luck

 

[TexasDan]

Incase u missed it, your injection pump DOES HAVE a hand primer on the supply pump.. it just has a white/clear plastic cover over it..
Remove the cover..and get a rider to pump the hp when it starts to stall and see if it doesn’t catch up..

another thing, I find it hard to believe that it doesn’t have a screen in the banjo bolt below the hp..

I see your inlet at the front of the pump, but do u have a return.??
If so, it’ll b a banjo bolt w a spring and ball in it.. it’s called an OVERFLOW VALVE..
It’s purpose is to hold fuel pressure in the fuel gallery..

If your loosing fuel pressure when u stall or turn it off.. either the overflow valve is bad(if equipped)
OR the valves in the supply pump ate the seats outta the supply pump.. and allowing the fuel to leak back/down.. or the piston in the sp is scored..
U can get a new sp for just about the cost of having a fuel shop to o/h it and there’s no telling if they’ll cut the seats or not.. it’s a crap shoot..
There’s a p# on the supply pump itself..

The hand primer pump was just replaced, that was the last repair that the shop tried. But when we we had gauges hooked up to the fuel system there wasn't a drop of pressure before the stall, but there was a gradual drop of pressure after the stall.

Next time I get out there I'll check that banjo bolt and look for a screen

 

[TexasDan]

thepumpguysc is spot on. That white plastic accordion piece is covering the hand wheel of the priming pump. The banjo bolt is underneath that component and connects the fuel line from the tank to that pump.

Take a photo of the monitor panel and post it here. There is a good chance that you can watch your travel pressures from the monitor panel. I just need to see what you have.

I'll try to get out there in the next two days to take a picture

 

[TexasDan]

BTW.. WHERE did u take the fuel pressure reading from.??
I like to take it at the inj. pump INLET.. but on your unit, it looks like there isn’t enough room.??
If it has an overflow valve, u can take it out and push on the ball or shake it to hear if the spring is broken..
Good luck

When we monitored the pressure we had a gauge hooked up between the fuel filter and hand pump.

 

[Kobelco ireland]

Looking at the dirt dirt on your lift pump I seriously don't think that was changed. But like said above bango screen is the first thing to check

 

[Delmer]

When we monitored the pressure we had a gauge hooked up between the fuel filter and hand pump.

Too many different stories, I can't believe them all.

 

[lmcnei3]

When we monitored the pressure we had a gauge hooked up between the fuel filter and hand pump.

New poster here;

I have a PC78US-6 SN 9319, and I'm dealing with exactly the same problem. I pulled off the Zexel supply pump yesterday, thinking it could be bad, to replace it with an aftermarket one($58 from amazon, PN105220-5960). The supply banjo bolt was full of crud/algae. Cleaned it off and replaced with the original pump, thinking the restrictions on the banjo bolt were the problem and maybe the pump wasn't bad. Machine was running poorly as it was before. Going to pull off the OEM supply pump and install the aftermarket in the next few days.

I've been troubleshooting this for a couple years, one of these days I will get it.

 

[Acoals]

But I was able to notice something when it comes to recreating the issue: Whenever I track somewhere it restarts the problem cycle. for example: If i go out to the machine, start it up and start digging a U around the machine, I can dig hard indefinitely with lots of power. If i track the machine 2 feet in one direction, when I stop and start using any function (swing, arm, boom, bucket curl), the machine bogs down and wants to stall. The second I try to perform work, the machine stalls. The machine will stall 2-3 times, and then the 3rd or 4th restart, the machine can dig hard indefinitely again. But again the second I move the machine it will stall. Additionally the machine will almost never push dirt well. I know the machine isn't meant to push dirt, but i can make a 1 foot high pile of soft broken up dirt (1-2 buckets of material), and if i try to push that dirt, the machine will stall.

It seems like if the machine will run properly for an indefinite period until it starts tracking the problem is not on the engine side, unless it is related to the vibrations cause by tracking.
Before moving the machine, when it is running good, perhaps use the blade and the boom to get the tracks airborne, and run the tracks in the air, without vibration or load.
Can you try to recreate tracking vibration by rattling the boom or striking down with it?
The basic idea I have is that the engine doesn't know where it's load comes from. Dig load is load, track load is load.

 

[TexasDan]

When we monitored the pressure we had a gauge hooked up between the fuel filter and hand pump.

Sorry man. I'm trying my best to explain what was explained to me by the mechanics that worked on the machine. Essentially the pressure was monitored immediately prior to the injector pump, and the mechanics told me the replaced part of the pump that bolts into the injector pump, I guess I got confused with how everyone is describing everything.. the mechanics either replaced the primer pump (trying my best here). I thought, incorrectly it seems, that hand pump, lift pump and primer pump were all different names for the same part (primer pump).

 

[TexasDan]

New poster here;

I have a PC78US-6 SN 9319, and I'm dealing with exactly the same problem. I pulled off the Zexel supply pump yesterday, thinking it could be bad, to replace it with an aftermarket one($58 from amazon, PN105220-5960). The supply banjo bolt was full of crud/algae. Cleaned it off and replaced with the original pump, thinking the restrictions on the banjo bolt were the problem and maybe the pump wasn't bad. Machine was running poorly as it was before. Going to pull off the OEM supply pump and install the aftermarket in the next few days.

I've been troubleshooting this for a couple years, one of these days I will get it.

Is it the same with your machine, in that, it gets worse after you track somewhere, but if you're just digging in one place it will work fine?

Also, is supply pump the same thing as the primer pump?

 

[TexasDan]

It seems like if the machine will run properly for an indefinite period until it starts tracking the problem is not on the engine side, unless it is related to the vibrations cause by tracking.
Before moving the machine, when it is running good, perhaps use the blade and the boom to get the tracks airborne, and run the tracks in the air, without vibration or load.
Can you try to recreate tracking vibration by rattling the boom or striking down with it?
The basic idea I have is that the engine doesn't know where it's load comes from. Dig load is load, track load is load.

I'm gonna be working for the next 24-48 hours, but I'll try to get back out to the machine as quick as I can and test this.

I talked to a mechanic over the phone and they were thinking it could be a "pump merge valve", I'm gonna do some more research on this and see if there are any diagnostic tests i can perform to check.

 

[Acoals]

Also, is supply pump the same thing as the primer pump?[/QUOTE]

No. The supply, or lift pump feeds low pressure fuel to the high pressure injection pump continuously during engine operation. The prime pump is for bleeding air out o the fuel system after service. Guys aren't always to particular about how they refer to things, either, so I am not sure exactly what is going on in your situation.

 

[Vetech63]

You need to bring up the hydraulic pressures on the monitor and observe them while operating different functions. From what I have read, this seems to be a travel function problem and not an engine problem.

 

[lmcnei3]

Is it the same with your machine, in that, it gets worse after you track somewhere, but if you're just digging in one place it will work fine?

Also, is supply pump the same thing as the primer pump?

My machine tracks very slowly, and curls in the bucket slowly if bring the boom in at the same time. Then it will stall out if i'm attempting to dig.