Hey everybody, New member and first time posting here. I recently purchased a used PC78 with ~6k hours on the machine. I wasn't able to test the equipment too much at the dealership (used equipment lot), but the machine appeared to operate well. After the machine was delivered I started to put it to work and noticed it was significantly under-powered. After working the machine for 10-15 minutes it began stalling very easily under almost any load, or sometimes no load at all, with any/all combination of functions (travel, boom, arm, curl, swing, counter-steer, push dirt with blade, etc). The machine is always operated with full RPM. The machine will immediately crank back up after stalling with no issues, and no error codes are indicated on the computer screen. The machine will put off a little dark smoke when immediately starting but after that it runs smooth (less than 2 seconds). If I wasn't operating the machine I have full confidence that it would run without stalling until the machine ran out of fuel. Also, until the machine bogs down and stalls it sounds like its running smooth. Also, when I'm operating the hydraulics there is no unusual noise coming from the hydraulic pump. When the machine bogs down and stalls it doesnt produce any noticeably colored smoke either. All the fluid levels on the machine are good, I replaced the fuel filter and hydraulic filter, tried running the machine with the fuel cap off (I read on another post that that could indicate something), and put clean fuel in the machine and treated with dry gas and algae killer, just in case. All had no effect. The fuel-water separator had no water in it, and very little dirt/sediment. I also checked the banjo bolts going to/from the fuel filter, they didn't have any screens or signs of clogging or dirt. My guess is maybe there are some more banjo bolts in the fuel system to look into. I'm pretty limited when it comes to mechanic skills, I have the basic skills, but if anyone has any ideas on what this could be, where to look, or things to do to test/troubleshoot or eliminate possible causes I'm all ears. Thanks for reading and any help provided. -Dan
Welcome aboard TexasDan. Sounds like you've done most of the simple things already. Check out this thread, sounds like those machines have a lot going on as far as operating and diagnosing the hydraulic/engine systems. HeavyEquipmentForums
Thank you sir, I'll review this thread right now. I thought I saw all the PC78 threads, but I missed this one!
Whats your serial number?
I would check your fuel flow and supply pressure 1st thing . Make sure you don't have a fuel line restriction between your supply pump and the fuel tank.
Had this very issue pop up today on a skid loader my guys are mistreating.
Yes your problem sounds to me like fuel starvation. There isnt a whole lot that can go wrong with a diesel engine that will allow it to run but not put in the work OTHER than fuel problems. A bad injector would make it run rough for example, a broken valve would be evident as well. If youre for certain that you have ample fuel supply and no air leaks - - check your intake for obstruction. Starving for air is just as bad as starving for fuel. All in all I have to rely on what a much older much wiser man once told me. "If your diesel engine wont run and you dont see a rod sticking out of the block, YOU have a fuel problem. You have started down the right trailL Fuel filter is number one. Check to see if you dont have any fuel lines that are cracking and allowing air into the fuel supply. I am not sure on your specific machine, but if you could somehow rig up a way to feed fuel gravity wise to the injector pump you could do that temporarily and see if that doesnt change the power situation.
If u have the inline injection pump, the banjo bolt that has the filter screen in it is the 1 under/below the hand primer..on the supply pump.. Good luck
Do you have one of these things bolted to the side of your injection pump? https://www.ebay.com/itm/2009537787...efaultOrganicWeb&_trksid=p2047675.c101224.m-1 See the two bolts in the plastic bag? one of them has a white ring sticking past the threads, that's a screen that UNSCREWS from INSIDE that bolt. That bolt is installed pointing down, remove it, remove the screen, clean it, put it all back together without loosing the washers. If it doesn't run right, replace any rubber fuel line.
Serial Number is 4030 Sorry I had some family come in to town and then I worked and just haven't had the time to put into this project.
All the pressures were good pre and post fuel filter, leading up to the pump. When there was a failure (stalling) the pressures would gradually go down to nothing.
Thanks for the reply, you seem to be quite wise as well. I should probably have put this out there in my first reply, just to catch everyone up. Here are where things stand now: After running out of ideas I contacted a local heavy equipment mechanic at White Star Equipment. The service manager I've talked through on the phone and all the mechanics that have came out on site have been great. First they noticed that fuel filter was not properly secured (it was broken off of the mounting portion of the fuel filter housing assembly and hanging up with wire). This led them to further inspect the areas immediately up and downstream of that. They noticed where the in/out lines going into the fuel filter have been rubbing for quite a bit, and they suspect it may have a small hole introducing air into the lines. They go to napa, replace the lines and restart the machine. Immediately the machine feels like it has a lot more power, and runs well, but then starts stalling again in 5 minutes. The mechanics look back in the engine compartment, see fresh liquid around the fuel filter, and now believe it must be the fuel filter housing assembly which is bad, and that is introducing air into the system. So they're about to leave the site with the intentions of ordering the part, returning tomorrow, and then everything is well. They turn around their truck and say lets just bypass the fuel filter to make sure. So they bypass the fuel filter and fuel is going right from the tank to pump. I test the machine again and it begins to run with a lot of power, and run a lot longer, well beyond the point it would normally fail. The mechanics were about to leave but I insist to stay just for a few more minutes. Right after is say that it feels like the machine bogs down. Ultimately it bogs down and then begins stalling again. The mechanic says he needs to come back the next day with gauges. They show up the next day with gauges. Check the pressure of fuel system. From tank to pump it was i believe above 50 PSI. when the machine would fail it would still have good pressure, then gradually return to nothing after stalling. The mechanics advised me a sudden loss of PSI followed by engine failure would indicate something in the fuel system (dirty tank, weird blockage, etc), however, engine failure followed by a loss of PSI would indicate the problem was in the injection pump. So back to your question. The fuel lines are in good shape, no concern for air getting in. The intake is very clean, no issue on the air side. I don't think there is a primer pump on this machine, because just prior to the injection pump the machine was getting 55psi on the fuel line. Would I be right to be right to assume the mechanics are correct on this?
Thanks for the reply. I don't believe my machine has one of these on the injection pump, but I can try and get back to the machine on sunday or monday to make sure.
Thanks for the reply, I will try and get to the machine on monday to get a good look, and then get back to this board to update everyone.
Gutsy move to bypass fuel filter when chances you have crap in your fuel tank are high. But now that it’s done here is my take: if you do not have a lift pump and you are counting on the injection pump to suck fuel….. then you’re looking for a vacuum between the tank and the pump. Not pressure. Have you removed the fuel cap to see if perhaps the tank is not properly venting?
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.
They're correct that the pressure dropping after the RPM drops is normal. But that assumes you have a mechanical transfer pump, so which is it? If the pressure that the injection pump sees is constant until the the engine slows and the engine slows before the pressure drops, then thepumpguy is going to need the numbers off the pump, unless he knows what it is from the serial number. Fuel filters are almost always under pressure from the transfer pump. Strainers, water separators are usually on the suction side, that is, between the tank and the transfer pump. So where's the transfer pump? follow the hose from the tank to the injection pump and back. I agree with CapnDean, bypassing the filter is a dumb move. Three reasons I don't like the guys, and I'll think of more later.
Isn't that machine equipped with a 3 cylinder yanmar and a DOC/DPF? Has anyone measured exhaust back pressure or unfastened the exhaust pipe to the muffler? Just a thought.
OK: I just read your mechanic report a second time. Machine runs fine, but after a while under load it stalls out. Bypassing fuel filter housing that you suspect is leaking.... allows machine to run strong much longer, but ultimately it loses power and stalls out. Could it be this? Your fuel tank vent is obstructed by a dirt dauber. So when you start the engine fuel can easily flow from the tank to the engine. As you use fuel faster than the air can enter the tank, you're creating a vacuum in the tank until the engine cant get enough fuel hence it starves. Removing the filter housing that was leaking simply eliminated that one other place that the system was getting vent air. Try this: run it til it stalls - - when it stalls, remove the fuel tank fill cap...... see if you hear a whoosh of air. What is truly telling in this situation is that after stalling....you are not having to bleed the injectors to get the fuel back to the cylinders. If it was truly a bad air leak - - in order to re start the engine, you would be having to prime the heck out of it. You know....how they say never let a diesel engine run out of fuel...
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.
My PC128, 228, AND 75 all had blockage issues at the bottom suck port, as did all my Takeuchi TL machines.
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?
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
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?
The 95 series engine would make sense for a gray market machine. That engine will have a suction strainer somewhere.
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 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 .
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.
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
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
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..
Someone is missing something simple I bet. Start from the beginning and don't assume anything.
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.
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.
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..
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.
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.
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!
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..
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.
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
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
I'll try to get out there in the next two days to take a picture
When we monitored the pressure we had a gauge hooked up between the fuel filter and hand pump.
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
Too many different stories, I can't believe them all.
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.
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.
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).
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?
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.
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.
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.
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.
I have the same problem as you with my 2007 US-6. Did you get yours fixed? Did you find that banjo bolt? I just ordered a camera snake to check my fuel tank. And a new monitor as mine stopped working from internal corrosion. Here's notes from my last encounter: Pc78 notes Control panel no power. Buy new one. Machine arm stick and bucket and rotate works fine The machine stalls instantly when the blade is lowered and extended to the end of its stroke. It also bogs down and stalls if I don't baseline travel controls when trying to travel. Can travel very slowly for a few feet at times then all of a sudden will stall. I can move a bit if I try to travel fast immediately but then stalls after a few feet. After it stalls and if I try to travel again immediate it will stall again. If I wait a minute then travel I can move a few feet again before it bogs down to stall. Possibly is worse after hydraulic oil warms up. If almost stall from tracks and then I try to spin the spin can cause to stall too. If one track lifted and free spinning. It may spin a few revolutions and then all of a sudden stall or gradually bog down and stall. Both sides. After a few bouts of near stalling from the tracks then extending bucket or spin or lifting boom or extending stick can cause the stalling as well. No difference if with engine rpm change. Fuel filter changed. Fuel tank full. Injectors were bled. No water in fuel.