Komatsu PC78 MR6 low power and stalling

[CapnDean]

He already ran it with the filler cap off, no change. Good thought though

I like a good puzzle. Injection pumps can go bad, but it’s not as often as you would think. Recommend you clean out that fuel tank for sure regardless of what final problem is. There is a business in Mobile AlaBAMA called Test Calibration that rebuilds these pumps relatively inexpensive. I took them one off an old Farmtrac tractor to get a $400 rebuild, the man came out of the back, said let me test it first. 10 minutes later her came back out and said “it doesn’t need a rebuild, i replaced the one o-ring that was torn..go put it back on”. No kidding! No charge.

 

[heymccall]

My PC128, 228, AND 75 all had blockage issues at the bottom suck port, as did all my Takeuchi TL machines.

 

[TexasDan]

I'm gonna go back to the machine on Monday and look back at all these comments. I really appreciate the comments and brainstorming by everybody. One thing that forgot to mention was the mechanics blew out the fuel line from the fuel separator to the tank with compressed air, the line seemed to take the air well and you could hear a lot of bubbling in the fuel tank. The mechanics were pretty certain that bad fuel or a crumy tank were not likely. Also the water fuel separator did not have any water or debris... not sure if that helps anyone's troubleshooting.

Good point about pressure vs vacuum. I guess that's a sure indicator that there is a transfer pump between the water separator and injector. Ill follow the lines with a inspection camera to find it, but how do I eliminate that as a failure point?

But thinking out loud, because the machine restarts so quickly and easily (and still stalls with the cap off), does that eliminate possible failure points prior to the injector?

I'll also take the inspection camera into the tank on Monday to rule out bad fuel/tank with certainty.

Does running the machine with the
Fuel cap off rule out a blocked dirt dauber?

 

[TexasDan]

Your machine serial number does not come up in my sources. I suspect it to be a gray market machine. Does the engine have one valve cover or individual valve covers? The engine with individual valve covers is a Cummins clone which does not have a strainer in a banjo bolt. It came with an inline fuel strainer that looks like an in line gas filter. If you find that filter, I would suggest you get a new strainer from the Komatsu dealer. The paper gas filters will swell and choke off the fuel flow and the engine will die and usually stay dead. The brass strainers will also do the same thing but you can take it out and blow air pressure through it backwards and clean it out the engine will run fine after that. One other thought is that on some machines the strainer is under the tank under the cab. Follow the fuel lines all the way back to the source to be sure.

I cant be sure off the engine right now before checking it physically, but based on the manual that came with the machine it's a komatsu 4D95LE-3-A

 

[CapnDean]

if running with the cap off and it still stalls out you have ruled out tank venting as an issue.

Your machine is starving for fuel for some reason. You’ll eventually find it. It will likely be something small too. Before I pulled the injection pump, I would do as you are doing - systematically from the fuel tank all the way to the injector pump. Replace fuel lines, replace filter housing, replace filters etc.. hopefully it’s the cheap thing.
I cannot think of anything that could be wrong in the injection pump that would exhibit these symptoms. How about a clogged or pinched return line? Do they return fuel to the tank unobstructed? Does the return flow appear to choke off before the machine stalls?

 

[John C.]

The 95 series engine would make sense for a gray market machine. That engine will have a suction strainer somewhere.

 

[Delmer]

You said, no "noticeably colored smoke" when it bogs down. Does it produce any visible smoke as it bogs down? Visible smoke would suggest a hydraulic problem, no smoke would suggest a fuel starvation issue.

Blowing air back to the tank might clear a blockage, and get better for a while. Or air can blow right around a blockage and sound clear, but still block fuel enough to choke an engine. Looking in the tank won't tell you much unless it's terrible.

Running without the cap will eliminate the cap being plugged, or other vent being plugged. Some injector pumps need to have free flow of fuel to the return back to the tank. Don't know if this is one or not. Restarting immediately just means it's not sucking much air, if enough air got in, then it would take many seconds of cranking before it restarted. I suspect if there's no air then the fuel vaporizes under vacuum, but immediately condenses and also pulls enough through the blockage to start immediately if there's no air leak.

Your mechanic's suggestion is correct, but they either screwed up enough, or it was miscommunicated enough, that I don't trust them.

I'm still thinking along with John C, that you have a strainer you haven't found, or a banjo bolt screen that you haven't found like I described in post#5.

Post some pics of the injection pump and any suspicious parts of the fuel system when you come back, if you don't fix it.

 

[NWH]

I hope this is not the problem with your machine but I recently had a problem much like you describe on my PC78US-6 and it turned out to be the hydraulic pump
Pressures were good and oil analysis showed no problems but it turns out there is a problem with the squash plate in the pump . A new pump cured the problem.
I have found this to be common problem with Komatsu. I have a good friend who also just discovered he has a bad pump on his PC78 with the same symptoms .

 

[CapnDean]

Cmon TexasDan....enquiring minds want to know

 

[TexasDan]

Cmon TexasDan....enquiring minds want to know

CapnDean, Sorry I had to punt it to a service center cause it was getting over my head, essentially what they did was:

Isolated the fuel system to see if the error could be recreated. The hooked up a 2 gal tank to a hand pump to the primer pump, just prior to the injection pump. The issue persisted so the thought everything prior to that in the system wasn't a problem (fuel, gunk in the tank, lines, filter, fuel filter housing, fuel water separator, etc).

The were certain it was the primer pump. The replaced it (took a month due to supply chain and covid issues at their shop. They said they ran the machine for a hard 4 hours never bogged down once. The machine got delivered back a few days later, I have the same issues. Im thinking about disputing the payment. Curious if ppl think I should. The mechanics were stand up guys, but it was a 3k repair, with no change in performance.

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.

If you would like to have a longer conversation I could talk over the phone, just shoot me a PM and I'll call ya.

 

[TexasDan]

You said, no "noticeably colored smoke" when it bogs down. Does it produce any visible smoke as it bogs down? Visible smoke would suggest a hydraulic problem, no smoke would suggest a fuel starvation issue.

Blowing air back to the tank might clear a blockage, and get better for a while. Or air can blow right around a blockage and sound clear, but still block fuel enough to choke an engine. Looking in the tank won't tell you much unless it's terrible.

Running without the cap will eliminate the cap being plugged, or other vent being plugged. Some injector pumps need to have free flow of fuel to the return back to the tank. Don't know if this is one or not. Restarting immediately just means it's not sucking much air, if enough air got in, then it would take many seconds of cranking before it restarted. I suspect if there's no air then the fuel vaporizes under vacuum, but immediately condenses and also pulls enough through the blockage to start immediately if there's no air leak.

Your mechanic's suggestion is correct, but they either screwed up enough, or it was miscommunicated enough, that I don't trust them.

I'm still thinking along with John C, that you have a strainer you haven't found, or a banjo bolt screen that you haven't found like I described in post#5.

Post some pics of the injection pump and any suspicious parts of the fuel system when you come back, if you don't fix it.

I make try to get out the machine today and take pictures. if you see this in time message me your number and I can send pics to you

 

[CapnDean]

I would not dispute the payment. I would take it back and say…. It’s not fixed. Let them throw more parts at it since that’s what they did

 

[thepumpguysc]

3k.!! A hand primer is less than 20.00.. THATS a lot of labor to diagnose a a “bad hand primer”.,
I to would take it back.,
Sorry for your troubles..

 

[Vetech63]

Someone is missing something simple I bet. Start from the beginning and don't assume anything.

 

[TexasDan]

3k.!! A hand primer is less than 20.00.. THATS a lot of labor to diagnose a a “bad hand primer”.,
I to would take it back.,
Sorry for your troubles..

I agree, im just concerned about bringing it back when they clearly have no problem charging a lot of money to not actually fix the machine.

Im gonna get another guy from Kirby Smith to come look at it. I talked to another mechanic and he told me it may be the pump merge valve, pressure control switch or auto decel switch. But essentially I need a true komatsu rep to come out and look at the bit codes, although, as i mentioned earlier it doesn't show any error codes when it stalls.

 

[TexasDan]

I would not dispute the payment. I would take it back and say…. It’s not fixed. Let them throw more parts at it since that’s what they did

Its not my style to dispute payments, but I tried to offer any other arrangement of renting out equipment, or getting mechanics to come out and look at it again, but their opinion was they spent so much time on the machine that they were actually giving me a deal. So essentially, they're not interested in fixing the problem any more, unless were starting from scratch with a fresh balance, and I'm not interested in that. Especially when I saw how the last 3k went.

Also their next recommendation was rebuilding the injector pump and I have no intention of spending 4k on that, as I'm starting to lose faith in the idea that the issue lies in the fuel system.

 

[thepumpguysc]

Can post a picture of the pump.??
If it’s to difficult to post here, u can send it directly to me..
just use my screen name @ aol.com from your home mail server..

 

[Delmer]

Could they at least answer some questions? like did they travel with the machine while they worked it? or did they just dig and not experience the problems?

 

[TexasDan]

Can post a picture of the pump.??
If it’s to difficult to post here, u can send it directly to me..
just use my screen name @ aol.com from your home mail server..

 

[TexasDan]

Could they at least answer some questions? like did they travel with the machine while they worked it? or did they just dig and not experience the problems?

They said they tested everything, but I don't believe it.