I recently bought a used PC35 with about 3,000 hours on it. I knew that it had this issue when I bought it, and I got an appropriate discount, but now it is time to diagnose and repair. I am very handy, but have zero experience with this kind of hydraulic equipment. The machine works fine when it is cold. But once it warms up, ie once the temp gauge rises off the peg to a normal operating temperature (I have not measured the exact temp at which this happens, and I don't know if it is engine temp or hydraulic fluid temp that matters), the engine will stall if any hydraulic function is run to the limit and held there even briefly. ie, when cold, the main relief valve and related relief components seem to work fine, but when hot, something doesn't work right and the engine stalls. I checked the idle and full throttle RPM, and they are to spec. The first diagnostic step in the shop manual is to check the Main Relief Valve, so as suggested I measured the relief pressure when this happens, and the pressure rises to about 24 Mpa just before the engine stalls. Main relief pressure spec is 26. So that seems ok - I assume that the failure mode is when the relief pressure is too high. My next move, based on the shop manual diagnostic flow for "Engine stalls", was to measure the differential LS pressure. When I started to look into doing that, I discovered a bunch of aluminum foil stuffed between the muffler and the main hydraulic pump. That led me to back to the shop manual, which shows (in pics) the muffler covered in some kind of insulation. That insulation is missing from my muffler. And part of the main hydraulic pump that contains the LS parts is closest to the muffler. Has anyone seen anything like this? Does the heat shield/insulation on the muffler seem important, important enough to cause part of the hydraulic pump to overheat if it is missing? Any hints, suggestions or guidance - esp of the form, "Oh yeah, every PC35 that I have ever seen has this issue when..." would be most appreciated.
You might consider giving a serial number so we have and idea of which Dash series machine you have. I've never had to spend any time working on the Komatsu minis so maybe someone will come along with better insights. As fas as the heat shield for the muffler goes,it is kind of important as the heat will bake the insulation on the wires going to any electric components. The heating problems usually started with the coolers and radiators which were not easy to clean on standard machines and is made exponentially worse on mine exes. Everything is tight and the counterweight many times has to be removed for access just to blow the dust out of the fins. As far as the hydraulics stopping the engine go, that shouldn't happen at all. As I recall, most of those machines had a single piston pump and a gear pump on the back that ran the blade and possibly the swing but I'm not certain of that. I think I have a manual somewhere but won't know if it applies to your machine unless you post a serial number. Does the cab on your machine tilt for access to the control valve?
Thanks for the reply John. Serial # is 09865. Machine is a PC35MR-2 . Canopy, no cab. This machine appears to have a single pump, with a single piston, but it has two output ports. I do not believe that there is a second, separate, hydraulic pump. The problem occurs when any hydraulic function, including travel, is used to the limit. The cab does tilt for access to the control valve.
I've never seen a PC35 so I'll leave that to John C, he seems to be the best answer you're going to get on some of those. You might be barking up the wrong tree looking at the hydraulics first. This isn't a big excavator with a more complicated hydraulic system with lots to go wrong, and lots of "optimization". This will be relatively crude and simple. How about the fuel system? What does the engine do when it stalls? sputter? dark smoke? no smoke? will it recover right away if you let off soon enough? or does it seem like it just switches off? I don't know that fuel system either, but I'd be looking for a cracked rubber fuel suction hose, or a plugged banjo bolt screen.
My source shows your machine to be an MR1 but it may be wrong which would mean you have a gray market machine. My source says there were no MR2 machines sold for domestic use in the US. I"ll see what I have for reference material and get back to you.
The data plate and placards are in English, which is no guarantee but suggests that the original destination market was the US. Also, I know this machine was owned by a local municipal government originally, which again argues against grey market. I can post a picture of the data plate if that would be useful.
All data plates for Komatsu that I have seen in the past dozen years have been in English. PM me your email address and I can send you a link with some information. The machine does have a single piston pump that has the ability to act like a double pump and it does have a gear pump mounted on the back of the piston pump. There were MR-2 machines sold here. It is possible someone messed with the controls on the pump or that there may a problem in the main control valve LS circuits. Look for broken paint on lock nuts for the pump and valve controls for clues concerning tampering.
My first instinct was fuel or air too! But the shop manual wants me to diagnose the hydraulics first, and my gut says that that is consistent with the actual behavior of the machine. That said, I had a generator with too much oil in the crankcase, and it would die in just this same way if you asked it to produce 220 instead of 110 (it had a switch). I changed the oil and filter, and replaced the air filter, first thing (with genuine Komatsu parts lol). I have a new fuel filter element and will replace that too. It certainly is possible that there is an issue with the fuel system that causes insufficient fuel to be delivered, stalling the engine. But why would that be temperature related if it was, e.g., a fuel filter problem? When the engine stalls, it feels like it is lugging, like the load is too high. No sputtering, smoking, coughing, or anything like that. It just slows down quickly and stalls. I would estimate that it takes maybe half a second to go from 2,500 RPM (approx) to stalled. It does that if you hold any hydraulic control to the full in or out position. If you hold the control for a fraction of a second, the engine starts to lug (RPM's falls). If you then release the hydraulic control, the engine returns to normal RPM. You can do that over and over. And again, it only happens when the machine is warm. When it is cold, you can hold the control at full all you want and nothing bad happens.
Are you saying that you have a service manual for the machine?
Yep, I have both the Shop Manual and the Operations and Maintenance Manual. There is a diagnostic procedure in the Shop Manual for "engine speed lowers extremely or engine stalls" - that is where I started (and why I measured the main relief pressure as my first step).
You could say the manual is designed for the dealer diagnosing new machines, and they will have more likely issues after 3,000 hrs. If a hose was cracked and sucking air, that would usually get worse as it got hotter. I'd like to see at least a little visible or dark smoke to indicate the engine was getting enough fuel.
I was going to send you the manual but since you already have one I think would be a waste. Maybe if I explain how the system is supposed to work it might help. It is a closed center load sensing type of system. The basics are that the pump supply a little more oil to the functions than is necessary. Trying to make it simple here, if the amount of oil you need is twenty gallons a minute, the pump will put out 23 gallons a minute. It is done by monitoring pressures. Output pressure of the pump is sensed on the torque variable control valve which also senses pressure on all the functions after flow leaves the main control valve. That is normally called load sensing pressure. The standard difference or "delta" is around 300 PSI normally. Load sensing "delta" is difficult to actually measure and Komatsu uses a special gauge that can sense both pressure and read out the difference or "delta." I usually do it with two gauges and note that they only show approximates as I have to figure the difference in my head. So I suspect what is going on is that the TVC valve is reacting too much and keeping the pump on stroke which pulls more horse power than the engine can produce. Study your book and try to find something that references the TVC valve and shows you where it is at. It will be on the pump somewhere but I haven't worked on this model of machine so can't tell you where it is and what it looks like. Usually it will be a big lock nut on a slotted bolt on the side of the pump. You will have to find out which way to turn it to back off the pump enough to quit killing the engine. Let us know what you find.
Right! Very helpful. On this machine, that TVC valve is called the LS valve. They ask you to measure the differential pressure using the special gauge that you mentioned. I tried to buy one, but can't find one for a reasonable price. So I will do as you suggest, and measure with two gauges then do the math. Now, here is the suspicious thing. The LS valve (or at least the ports that you measure the differential pressure from) are on the back of the hydraulic pump near the muffler. My working theory is that the muffler, which is missing its heat shield, is overheating some component in the LS valve, which is causing it to (as you suggest) fail to do its job once the machine gets hot. I will measure the LS differential pressure while both cold (and thus working fine) and hot (and thus not working fine) and report back. Thanks very much to everyone for their help and suggestions, I really appreciate it very much!
I'd like to see fuel pressure after the lift pump, both at full throttle unloaded and loaded. Certainly that will be a lot easier to measure
Turns out that there is neither a spec for fuel pressure in the Shop Manual, nor a procedure for measuring it... Anyone have a sense of what proper fuel pressure might be?
As I recall those have an electric fuel pump and they work or they don't. The the line off at the fuel injection supply connection and see if fuel comes out when you turn the key on.
Ok, I have made some progress, but am definitely stumped. I tested the Main Relief Valve, and it appears to function normally. I also tested the LS valve (the differential pressure valve that controls the variable output pump), and it also appears to function normally. By "function normally" what I mean is that while the machine is "cold" I can measure the pressures and they are correct by the book. When the machine is not, I can't measure the pressures because the engine dies when I try to do so, but they seem to be trending normally immediately before the engine dies. But more importantly, while conducting these tests, I verified that the machine operates completely normally when "cold", and that the engine quits predictably and reliably (and very quickly) if any hydraulic control is run to the limit while the machine is "hot". I need to run more detailed tests, maybe with a temperature measuring device installed, but it appears that "cold" = engine temp gauge on the peg (which I assume also means that the thermostat between the block and the radiator is still closed). "Hot" = any movement of the needle off the peg, which I am guessing correlates to the thermostat opening. The one other data point that I have is that when I went to replace the air filter elements (mine has dual elements), I found an old thermostat sitting on the air filter housing. That suggests to me that someone else went down this road - and perhaps replaced the thermostat (or took it out and left it out, I have not verified that there is one installed currently). I am now beginning to think that this must be an engine problem, most likely a fuel problem, and not a hydraulic problem. I just can't figure out any reason for the hydraulic system to be effected by engine temperature. There is no hydraulic fluid cooler associated with the radiator. I did insulate the muffler, which is close to the hydraulic pump, and that made no difference at all. Anyone have any thoughts about what to check in the fuel system, or how to plumb in a fuel pressure sensor? This machine has a Komatsu 3D88E-5P Diesel engine. I suspect that there may be a shop or MX manual for the engine that is separate from the book for the machine, I am going to go look and see if I can find it. Maybe it will shed some light on the fuel system.
what kind of hoses and fittings are the fuel supply to the injection pump? get a tee and run a line to the cab with a pressure/vacuum gauge so you can see what the pressure is at idle, high idle, and under load cold, , then hot. The specific fuel pressure isn't so critical to me, more looking for it to stay somewhat steady. If it drops off with engine load more when hot, then you have something to check further. How about some pictures of the fuel filters, lines, and injection pump? There's a few components that LOVE to fail, that are easy to ID from pictures, but I'd be guessing what you have without a picture.
I will take some pics tomorrow and post them. Turns out this machine has three fuel pumps. Maybe everyone knew that except me lol. An electric pump to get fuel out of the tank. It is positioned between the water separator and fuel filter behind the engine, and is very easily accessible. An intermediate pump that they call the trochoid pump (built in to the main injection pump) that raises the pressure to the required input pressure for the injection pump, and then the main engine driven injection pump.
I forgot to mention (again) sucking air, you could run the return into a section of clear tubing, or into a glass jar to see if there's any air bubbles when it stalls.
Hey. I’m from Sweden and I’ve got a komatsu Pc 35 like you. Whit exactly the same problem. I have change the main hydraulic pump. But it is still the same. I just curious if you did find out what’s wrong with your machine? My English is not perfect sorry. / drevern
Any updates on this machine ? Mine has same problem ..
Its a bad hydraulic pump, gate will stick when it gets to operating temp. Not rebuildable, and before you spend 6k on a pump check your compression those yanmars are pricey to rebuild.
This thread is as old as the wind but i have the exact same issue. When the rams reach limit with control engaged it will almost stall. finally hit full overheat and i shut down then it would not start because the pump seems to be on full output. tested the main supply from the pump and getting 4000 psi when turning the engine over but would not start. disconnected the hose to a pail and it started right up. I am not sure if its a Swash issue or the LS Valve. any further steps to diagnose before purchasing a new pump? $$$$ thanks in advance 20007 PC35MR-2 SN-9736
I welcome all members. I have a komatsu PC35MR produced in 2006. I need a pdf to see the hydraulic system diagram. If anyone can help us, where it can be downloaded and in what way, we would be grateful. I have a problem when the machine warms up, and after a while the hydraulics become too slow, so I have to turn off the machine and wait 1 hour for it to cool down. I assume that something is wrong with the hydraulic system.
have any of you tried heavier hydraulic oil? I 'fixed' a kubota tractor that way years ago - it used some AW15 lightweight oil for it's hydrostatic transmission. tractor had over 4k hours on it - which for a little one like is about half-life I think. anyway, went to see the guy - he wanted to sell it for $1k, and really I should have just bought it. But I felt sorry for the guy, and told him to just put AW46 in it and see. The pumps are worn, your tractor works great cold, but not well warm. it's the oil viscosity slipping through tolerances greater than it's ready for. That tractor is still working today - on AW46. As I recall, it had an Eaton hydrostatic in it. Betting your pumps are the same. These aren't my rigs, but I do it on my stuff. On my old 83 Backhoe, I no longer run that thin HyGuard in it which is 20W I think. I run AW46 made by Hyperion (??), they sell it at my local tractor shop. Seems like good oil, the old 410B has been running just fine one it -in both the drive clutch and main hydraulic reservoirs. If these are commercially used machines, probably you should fix them professionally. If they are just homeowner machines that you are on the short end of the stick already... give this a shot, I bet you are pleasantly surprised.
Well said!!
Thank you, I'll try to do that too, maybe it'll be good for a while.