Need Help with Komatsu PC55 **Possible Hydraulic Issue**

[Amjad.kamal]

I have a Komatsu PC55-MR3 that I purchased from China and got it shipped here in Calgary, Canada. The machine was dropped at a Komatsu dealership and they filled up the machine with fluids and diesel and performed the following work:

1. Filled hydraulic fluid, engine oil & coolant
2. Change the hydraulic oil filter, engine oil filter & air filter
3. Fixed oil leak from the rear main (broken coupler replaced)
4. Changed the joystick pattern from some weird pattern to ISO pattern (saying weird because the service department guy said I've never seen an excavator move like this ever in my life)

The excavator is now at my place and I am experiencing a major issue with the hydraulics (or at least I think its hydraulics). The engine issues mentioned below are issues but I am not sure if its critical or contributing to the major issue. But I may be wrong. I personally have zero past experience with excavators at all or with hydraulics. However, I've read, re-read and then some more, and continuing to do read the Shop Manual focusing more on all the hydraulic components. So please consider me to be a complete novice.

Hydraulic Issues (Main Issue):

1. When trying to move the tracks/travel or any of the work equipment (without any load in the bucket) it moves and then suddenly stops (with a small but noticeable jerk; like something tripped). All work equipment and travel stops working (joysticks become unresponsive so does the travel levers). However, the swing and the blade continues to work. Turn the engine off and fire it up again and everything works till it'll happen again under the same circumstances. Few observations below
   
   1. If the throttle is set low-medium this happens almost immediately upon trying to move the tracks or lifting the boom.
   2. Happens almost immediately if boom and arm are operated at the same time at low-medium throttle.
   3. At full throttle, I am able to move the equipment very gradually and slow. If pushed too much or too quickly it would result in the same issue described above.
   4. Even at full throttle the engine seems to bog down a little when putting the load before the hydraulics function for the work equipment trips. However, I have noticed the hydraulics tripping even without noticeable bogging down of the engine.

Engine Issues:

1. The engine (Yanmar 4D88E-5XA) seems to be misfiring at full throttle
2. Engine produces excessive white smoke at the start and for about 15-20 mins till it fully warms up (smoke significantly reduces but still present)
3. Engine Oil excessively black despite being recently changed (2 months ago and hardly any run time)

What I have checked so far:

• Checked Unload Pump Pressure: Within specs of standard value ~500psi
• Checked the relieve pressure of the boom, arm, bucket & Travel
  • Boom, arm & bucket relief are ~900 psi higher the standard value as per the workshop manual (4700psi vs 3845 psi)
  • Travel relief pressure ~590 psi lower than standard value (3250psi vs 3845)
• Checked Swing & Blade relief pressure
  • Swing relief pressure is about 250 psi higher (3100 psi vs. 2845psi)
  • Blade relief pressure is ~3200psi right around where it should be (3200psi vs. 3133 psi)
• Checked the Hydraulic Oil filter for any metal shavings or glitter - none whatsoever

Some more History of the Machine:
This is obviously a gray market machine (imported from China). Engine hours and model year cannot be certainly determined. It's a 2019 model allegedly (both the dealer and I highly doubt that's true). Dealer thought maybe anywhere between 2012 to 2015; but it’s just a guess. The seller showed me videos of the machine operational (you decide how much weight you'd want to give that?). The machine was unloaded at local Komatsu dealer in Calgary. I asked them to change the joystick pattern to ISO. If I were to believe that the seller sent a machine that was functional and working; then the hydraulic related issues seems to have started after the dealer changed the pattern. The machine doesn't have a multi-control valve so the dealer must have moved the hydraulic lines and the ppc lines on the control valve. The Machine doesn't have a Control Unit; seems it was pulled out so really can't hook up a computer or anything. The dealer after giving me a big bill basically gave up and asked me to take it work on it myself as my summer project .

I am looking for some expert opinions and guidance on what you think may be the issue OR what should be my troubleshooting steps be next. Any help on this would be hugely beneficial for me and much appreciated.


Thanks.

 

[Vetech63]

YIKES!!! I assume this was a used machine?

1. The engine (Yanmar 4D88E-5XA) seems to be misfiring at full throttle
2. Engine produces excessive white smoke at the start and for about 15-20 mins till it fully warms up (smoke significantly reduces but still present)

These 2 are related. Its sound like a failed injector (not atomizing the fuel correctly)

Engine Oil excessively black despite being recently changed (2 months ago and hardly any run time)

This may be normal providing the engine is equipped with an engine oil cooler. It doesn't take much black oil left in a cooler or oil galleys to turn fresh clean oil black. This is oil that doesn't drain from the pan.

You really need to correct the engine problem before you move to the hydraulic problems. Some hydraulic conditions are directly affected by your engine performance and torque curve .

 

[Entropy1]

I had a similar issue on my PC-128. It was the PPC lock-switch/solenoid circuit giving me trouble. The PPC solenoid valve diverts the 500 psig pilot-pressure back to the tank (making the hydraulics appear dead). Normally when you lift up the handle to get into the machine, the PPC switch shifts the solenoid valve (making it safe to enter/exit the machine - should you bump the controls). Put the handle down, 500 psig pilot pressure is available to the main valve body.

The PPC solenoid can go bad electrically (intermittent performance). The hydraulic portion of the solenoid valve can go bad (become sticky). The PPC switch under the machine's handle can go bad (intermittent performance). The wiring could be dirty (intermittent performance).

Based on what you've described, I would replace the PPC solenoid first. It sounds like a weak/worn solenoid issue. Next I'd replace the PPC electrical switch. You could troubleshoot further before buying parts (aka install a current meter in-line with the PPC solenoid, and observe for a current change during the fault) - but these particular parts aren't that expensive.

I don't have the hydraulic circuit for your machine. I would assume a malfunctioning PPC valve would kill everything (including blade & slew) - but maybe not? You'd have to check the diagram.

What you are describing sure sounds like an intermittent electrical issue - which being a Komatsu, is most likely a solenoid going bad. Note: a weak solenoid could be impacted by hydraulic pressure changes/flow on the hydraulic side of the solenoid valve - leading one to falsely believe the problem is not electrical.

 

[Entropy1]

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If you have trouble obtaining PPC parts (availability or cost), you can replace the PPC valve with a manual valve (example linked above). Route 500 psig supply line in. Push down to route oil back to tank (controls deenergized). Pull up to route oil to main controls (controls energized). It will completely eliminate the electric side of the PPC circuit.

 

[Amjad.kamal]

I had a similar issue on my PC-128. It was the PPC lock-switch/solenoid circuit giving me trouble. The PPC solenoid valve diverts the 500 psig pilot-pressure back to the tank (making the hydraulics appear dead). Normally when you lift up the handle to get into the machine, the PPC switch shifts the solenoid valve (making it safe to enter/exit the machine - should you bump the controls). Put the handle down, 500 psig pilot pressure is available to the main valve body.

The PPC solenoid can go bad electrically (intermittent performance). The hydraulic portion of the solenoid valve can go bad (become sticky). The PPC switch under the machine's handle can go bad (intermittent performance). The wiring could be dirty (intermittent performance).

Based on what you've described, I would replace the PPC solenoid first. It sounds like a weak/worn solenoid issue. Next I'd replace the PPC electrical switch. You could troubleshoot further before buying parts (aka install a current meter in-line with the PPC solenoid, and observe for a current change during the fault) - but these particular parts aren't that expensive.

I don't have the hydraulic circuit for your machine. I would assume a malfunctioning PPC valve would kill everything (including blade & slew) - but maybe not? You'd have to check the diagram.

What you are describing sure sounds like an intermittent electrical issue - which being a Komatsu, is most likely a solenoid going bad. Note: a weak solenoid could be impacted by hydraulic pressure changes/flow on the hydraulic side of the solenoid valve - leading one to falsely believe the problem is not electrical.

Are you referring to the 2-spool solenoid valve in the picture? If so, I forgot to mention that this was replaced by the dealer.

 

[Amjad.kamal]

YIKES!!! I assume this was a used machine?

These 2 are related. Its sound like a failed injector (not atomizing the fuel correctly)

This may be normal providing the engine is equipped with an engine oil cooler. It doesn't take much black oil left in a cooler or oil galleys to turn fresh clean oil black. This is oil that doesn't drain from the pan.

You really need to correct the engine problem before you move to the hydraulic problems. Some hydraulic conditions are directly affected by your engine performance and torque curve .

Thanks! I'll look into the injectors and see if I can replace them.

 

[Amjad.kamal]

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If you have trouble obtaining PPC parts (availability or cost), you can replace the PPC valve with a manual valve (example linked above). Route 500 psig supply line in. Push down to route oil back to tank (controls deenergized). Pull up to route oil to main controls (controls energized). It will completely eliminate the electric side of the PPC circuit.

What I am struggling to understand is that if its pilot line/pressure related issue how would the swing and the blade continue to operate while I loose boom, arm, bucket and travel. Wouldn't the PPC switch/solenoid related issue kill the entire pilot pressure feed?

 

[Entropy1]

There could still be a problem with the circuit. There's a minimum amount of voltage/current required for the solenoid to throw with full force. An undervoltage condition - aka dirty wire connectors, dirty contacts within the PCC switch, even some corrosion on a fuse - can drop enough voltage to keep the solenoid from switching like it should. Why was the old solenoid replaced? It is safe to assume that the technician suspected a PPC problem. And more importantly, did the replacement actually fix the problem? It sounds like it didn't.

To positively confirm (or eliminate) the PPC circuit as being at fault, you'll need to install a pressure gauge downstream of the PPC valve (on the pressure inlet side of the controls circuit - not on the pressure-inlet side of the PPC valve). If gauge pressure drops when the machine is malfunctioning, you've got a PPC fault (or remote possibility of a pump issue). If the pressure holds steady at 500 psig when the machine is malfunctioning, the problem is NOT associated with the PPC circuit.

 

[Entropy1]

Does your machine have an offset boom? If so, there are other solenoid valves in your machine that will prevent arm movement in certain conditions (aka driving the bucket into the operator's cab). In this case, just the arm controls would die - but not necessarily the slew & blade. You'll need to download the maintenance/troubleshooting manual.

EDIT: you need to dig into the manual. Look at the hydraulic circuit and the electrical circuit for your specific machine. Find the fault combination (component malfunction/failure) that results in the symptoms you're seeing. The good news is that intermittent control problems are usually electrical, not mechanical (pumps are expensive).

 

[Entropy1]

Komatsu excavators with offset boom have rheostat sending units in the boom/arm. When these go bad, you can get quite irritating intermittent control faults. Again, the fault signal triggers a solenoid valve (on the 500 psig side) and stops movement for that portion of the control circuit. Not saying this is your problem, but it could be. It would explain why only some circuits in your machine stop working (as you've pointed out, the PPC fault normally stops all motion).

 

[Amjad.kamal]

There could still be a problem with the circuit. There's a minimum amount of voltage/current required for the solenoid to throw with full force. An undervoltage condition - aka dirty wire connectors, dirty contacts within the PCC switch, even some corrosion on a fuse - can drop enough voltage to keep the solenoid from switching like it should. Why was the old solenoid replaced? It is safe to assume that the technician suspected a PPC problem. And more importantly, did the replacement actually fix the problem? It sounds like it didn't.

To positively confirm (or eliminate) the PPC circuit as being at fault, you'll need to install a pressure gauge downstream of the PPC valve (on the pressure inlet side of the controls circuit - not on the pressure-inlet side of the PPC valve). If gauge pressure drops when the machine is malfunctioning, you've got a PPC fault (or remote possibility of a pump issue). If the pressure holds steady at 500 psig when the machine is malfunctioning, the problem is NOT associated with the PPC circuit.

Would this be the right test?

 

[Amjad.kamal]

Komatsu excavators with offset boom have rheostat sending units in the boom/arm. When these go bad, you can get quite irritating intermittent control faults. Again, the fault signal triggers a solenoid valve (on the 500 psig side) and stops movement for that portion of the control circuit. Not saying this is your problem, but it could be. It would explain why only some circuits in your machine stop working (as you've pointed out, the PPC fault normally stops all motion).

Yes, originally it has boom swing but its disabled on this machine. I'll have to look into it's ppc valve under the hood. However in the cabin the control for boom swing is welded so it can't be operated. Here is the hydraulic layout of the ppc valves from the shop manual.

 

[Entropy1]

What do you mean the control for the boom swing is welded? You are talking about the boom offset? Where is it welded?

If you haven't purchased a gauge & adapters yet, there is a way to troubleshoot without them. It's crude, but often works well. You'll need to uncover/access the main valve body. Loosen the 500 psig pilot line going to the blade spool valve (either the raise or lower - whichever is easiest to access). You don't need to fully disconnect it. Just loosen it up. Do the blade first because it's known good (working).

Then carefully have someone attempt to raise/lower the blade and watch for oil spitting out past the threads. Take visual note - this is what presumably good 500 psig pilot pressure looks like (observed weeping/spraying past the loosened threads).

Tighten the blade line up, then loosen up the boom (raise or lower). When the machine is malfunctioning, carefully have someone attempt to raise/lower the boom and watch for oil spitting out past the threads.

Conclusions: no oil spray means you have a problem on the 500 psig side of the control circuit. If you have oil spray with no movement, it means there's likely a problem with the high-pressure side of the pump.

 

[Amjad.kamal]

What do you mean the control for the boom swing is welded? You are talking about the boom offset? Where is it welded?

What do you mean the control for the boom swing is welded? You are talking about the boom offset? Where is it welded?

If you haven't purchased a gauge & adapters yet, there is a way to troubleshoot without them. It's crude, but often works well. You'll need to uncover/access the main valve body. Loosen the 500 psig pilot line going to the blade spool valve (either the raise or lower - whichever is easiest to access). You don't need to fully disconnect it. Just loosen it up. Do the blade first because it's known good (working).

I do have the pressure gauges but it seems I am going to need an adapter (which is showing to be 500 bucks for what seems to be a t-adapter). I think your suggested method would be a good start to rule out no oil pressure on the pilot line.

I'll report back here when I get a chance to do the test.

Thanks!

 

[Amjad.kamal]

Alright, so the pilot pressure line is not the issue it seems. I tested like you suggested as well as with a pressure guage. Both before and after the fault occurs I have about 550 to 600 psi of pressure.

I tested on the boom raise port on the control valve. Hooked up a pressure gauge to it. Got 550 psi. Then I forced the failure by putting load on the tracks and got a trip sort of situation (no motion in travel, arm or bucket). Pulled the joystick to raise the boom and the gauge read around 550 psi again.

 

[Entropy1]

If the pilot controls are sending the proper pressure to the main valve body, and the machine is not responding, it can only mean the high-pressure pump is not making pressure. If your PC-55 is like my Takauchi, there's a twin variable displacement pump for the main machine functions, with a small positive-displacement gear pump on the end (which drives just the slew and blade).

It has been my experience that when hydraulic pumps go bad, it's not intermittent. They either catastrophically fail, or progressively lose pressure. Thus I would hold out hope that something is commanding your variable displacement pump to idle. Hopefully it's not a fault within the pump itself.

I would dig into the troubleshooting guide - for troubleshooting the high-pressure circuit.

 

[Amjad.kamal]

If the pilot controls are sending the proper pressure to the main valve body, and the machine is not responding, it can only mean the high-pressure pump is not making pressure. If your PC-55 is like my Takauchi, there's a twin variable displacement pump for the main machine functions, with a small positive-displacement gear pump on the end (which drives just the slew and blade).

It has been my experience that when hydraulic pumps go bad, it's not intermittent. They either catastrophically fail, or progressively lose pressure. Thus I would hold out hope that something is commanding your variable displacement pump to idle. Hopefully it's not a fault within the pump itself.

I would dig into the troubleshooting guide - for troubleshooting the high-pressure circuit.

You are correct, it is a variable displacement pump like yours with a gear pump in the middle for swing and blade.

I tested pressure port 1 and 2 with the pressure guage. At idle the pump reads 500 psi which is as per the specified range. Then when the fault occurs the pressure drops to zero. In other words something is causing the pump to stop producing any pressure at all when the fault happens. And as soon as you power cycle the machine the pump is giving out the 500 psi unload pressure till the fault occurs again under load.

My next guess is the pump regulator. There is solenoid on the pump that I can't figure out what it does exactly. It's right next to the pc adjustment screw. Picture below in case you know what it does. The interesting thing is that when I disconnected the solenoid wire, it made no impact at all on the operation or the fault.

 

[Entropy1]

Have you checked all the other easy stuff? Hydraulic tank oil level? Return filter? Kinked/collapsed pump suction hose? New pump is not cheap. You'll want to check all the other longshots first. The worst thing in the world is replacing an expensive component, only to have the same fault. . . .

Not sure what the solenoid/component does on that particular pump. I would absolutely look into it more. Does the service manual identify any pump adjustments, and/or troubleshooting steps? (other than pump replacement)?

 

[Amjad.kamal]

Have you checked all the other easy stuff? Hydraulic tank oil level? Return filter? Kinked/collapsed pump suction hose? New pump is not cheap. You'll want to check all the other longshots first. The worst thing in the world is replacing an expensive component, only to have the same fault. . . .

Not sure what the solenoid/component does on that particular pump. I would absolutely look into it more. Does the service manual identify any pump adjustments, and/or troubleshooting steps? (other than pump replacement)?

I've ruled out the easy stuff like the things you've mentioned. I agree with you and I am not willing to replace/repair the pump until I am reasonable sure that it is a pump related problem. It doesn't seem like it because the symptom is quite unique in the sense that all the troubleshooting scenarios from the shop manual talk about either slowness, lack of power or no work equipment function at all; but nothing like what I am experiencing where the pump completely stops producing output/pressure once the fault occurs. With my minimal knowledge and understanding it seems that its got to be electrical as power cycling (shutting down the engine and turning it on again) somehow resets the pump, and oil flow/pressure returns immediately and then goes out once the fault occurs under load.

There is a section in the shop manual to measure and adjust the LS pressure and adjust it. Also a section to adjust the PC valve. Both of these are pump tuning related. As per my understanding the LS pressure coming into the pump from the control valve moves the spools in the regulator to keep the LS and pump discharge differential pressure constant by increasing/decreasing the pump discharge. The LS pressure is adjustable. Once its set per spec the manual calls for PC adjustment if engine bogs down under pressure (which is something I am experiencing). But I need to test/adjust the LS pressure before I touch the PC valve according the manual.

Challenge is that I need a T-adapter on the LS line on the pump side (as it doesn't have a pressure plug) that is for 500 bucks! I really can't wrap my head around 500 dollars for an adapter which sounds like a regular T where I can connect the line on one end, attach the T to the pump and plug in the pressure gauge on the T. Am I missing something? Do you think there is something special about this adapter (L2) in the image below? This really where my lack of experience with hydraulics kick in .

 

[Entropy1]

The most unique thing about Komatsu is Komatsu threads. They use 30-degree metric threads, which are inappropriately expensive IMHO. They can't use 37-degree JIC & SAE like the rest of the world. Even BSPP fittings on Takeuchi are tolerable (price and availability wise).

You don't need to by a high-end Komatsu test gauge with quick disconnects. Recommend getting the items below. These are surpluscenter.com part numbers. Note: the 6-foot 1/4" hose might be overkill, but it will last a lifetime, and you can put the gauge within eyesight when you're in the cab troubleshooting.

Gauge, 600 PSI 2.5" ITEM NUMBER: 21-1246-G
Gauge, 5000 PSI 2.5" ITEM NUMBER: 21-1246-L
Hose, 1/4" x 72" JIC 4F Assy 5800 PSI, ITEM NUMBER: 920-2272
Adapter, JIC 4 Male x 1/4" NPT Female Straight, ITEM NUMBER: 9-2405-4-4 (x2 - one for each gauge)

For the other end of the hose, Surplus Center (link below) offers adapter fittings for JIC-4 male to various other threads (NPT, SAE, BSPP, ORFS) - unfortunately they do not sell 30-degree Komatsu adapters (you must shop elsewhere for those). Looking at your picture above, those fittings appear to be straight thread with o-ring seal, not 30-degree Komatsu - presumably metric. Get yourself a set of SAE & Metric thread pitch gauges, and also a dial-caliper (if you don't already have them). Use these to positively identify the threads required to construct your tee. Find a suitable tee through Parker (bottom link) - the hardest part will be adapting the tee to JIC-4 Male on one end (to connect your gauge hose).

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https://www.parker.com/content/dam/Parker-com/Literature/Tube-Fittings-Division/4300_Catalog_Cover.pdf

Additional notes: If you are unable to find an adapter thread-combination that works (without spending 500 dollars) - you can TIG weld fittings together to "force" them to adapt. If you end up doing this, recommend you stick with 300 stainless fittings only. The steel adapters sold through Surplus Center are made from free-machining carbon steel and are not suitable for welding (high risk of cracking when welded). If you buy 300 series stainless fittings through Parker, they will weld together just fine when welded with 308 filler rod.