Hello, Troubleshooting a 277C S/N:JWF00898. Having an issue where the machine is bogging down when using the lift and tilt cylinders. It seems to be more common when at lower RPM than wide open. Engine bogs, shakes, and drops about 400-600 RPM when this happens. little to no smoke(smoke that is seen is faintly grey). No codes, no issues noticed when trying to run the drives. Forwards and backwards does not cause the bogging, but sometimes it feels like the machine is not moving as fast as it should at that RPM. I cannot find a diagram of the hydraulic system so i can only run on an assumption. But i am thinking that there is possibly a valve for the lift/tilt controls that is not opening/closing all the way? I have confirmed that the turbo is functional and the air is not restricted. I have also confirmed plenty of fuel flow to the high pressure pump. I have a good feeling that this is hydraulic related. I am going to start with the easiest option and switch the hydraulic filter. Is there any resources for schematics or diagrams of the hydraulic system? Is there any use in testing the pressures of the test ports? I have checked in ET and cannot find any anomalies or codes. Thanks!
I think the first thing you have to take into account is that the drive system and implements are supplied by separate hydraulic pumps. The only thing common between the two systems is the hydraulic tank. So it's quite possible to have a machine that drives fine but has problems with the implements. I would suggest to change the hydraulic filter as a first step then cut the old one open, remove a section of the filter media and look for sparklies. If the filter is clean and free of debris then it's on to pressure testing.
Nige this appears to be a high flow machine. If memory serves there's a service letter on this problem. Think you could pull it up.
No access at the moment. Maybe @heymccall can help.?
I replaced the hydraulic filter this morning cut open the old one and found, what i think is, little to no material in the filter. The photo shown is the most i could find in the ring i cut out of the pleats. I put the new filter in and ran the machine. At all RPMs forward and reverse caused no issue turns, quick changes of directions, nothing would bog the motor. Ran the quick coupler open and closed a few times and no bogging. As for the implement controls. Raising the bucket dropped the RPMs a little lowering the bucket caused a major disruption like before. Rolling the bucket dropped the RPMs about equally in both directions. I did notice that on the roll, if i rolled the bucket back the RPMS would drop if i let go the RPMs would hold at this lowered rate, and if i slightly rolled the bucket forwards it would stop and the RPMs would rebound. This test seems to eliminate the possibility of the issue being the fuel system, air restriction, or anything outside of the implement pump circuit. It also seems to be possible that it is a location that is shared between the lift and tilt controls as it seems unlikely that both the tilt and lift valves have simultaneously failed. That points me to the pilot valve as the most likely culprit. Thoughts?
I agree. This reeks of an implement pump control circuit issue. You really need to run through the Test & Adjust procedures for the high flow implement pump. Also be checking pilot pressure, would be nice to rule that out completely too. Hopefully someone can post the procedures/specs for those. Your implement pump and control circuit is fairly straight forward. It's a variable displacement piston pump that uses a 'signal' pressure from your implement control valve. The signal pressure is what tells the implement pump to stroke up or down, changing a swashplate angle inside the pump which controls pump displacement/output. The pump control valve is a little block-looking thing attached to the pump that has two little spools in it, mounted underneath the pump in your photo, and it's function is to take this 'signal' pressure and stroke the pump (change the swashplate angle) so that pump output pressure is roughly 350 psi higher than the signal pressure. Once we've confirmed pilot pressure is ok, there's two pressure ports you need to stick gages on. One is on the little pump controller block under the pump I mentioned... it reads the signal pressure coming back from the implement control valve. The other is on the implement control valve... it reads implement pump outlet pressure. From your statement... I would love to know what both the signal pressure and pump output pressure are doing while the RPMs are stuck at this "lowered" rate while you're not commanding anything. Re the filter, standard practice is to fold the pleats back up and squeeze out the oil in a vice, then run a torch over it and look for shiny bits. That picture you posted looks promising though.
I was thinking pilot pressure was a good place to start also. Not sure what pressures i am looking for but my test kit should be here tomorrow so I am going to do some testing on those three ports and see what things look like. I will report back. I also pressed and burned the filter. Filter material was very flammable and just caught fire. However after pressing little material presented itself. So i still feel confident that the implement pump is okay.
When @Chrisso said "then run a torch over it" he meant use a flashlight, not set fire to it........!! Pilot pressure test attached.
Hmm is this potentially one of those cultural differences ie Rice Bubbles versus Rice Krispies deals?
When I saw "torch" and "shiny" I was 100% certain i was looking for the brass filings to glow under a flame! It must be in my nature to veer to the side of destruction! Planning to run the attached pilot pressure test once I receive the test kit. For now I will be putting away all sources of fire as I do not believe they will be needed for any further testing. LOL!
Wrong procedure attached above. Yours is a High Flow machine with a load-sensing variable displacement pump so it has a different testing procedure. See attached.
Thought this might help it is simplified version of the c series XPS hyd system This illustration shows the optional High Flow XPS Hydraulic System. The High Flow XPS system features a load sensing, pressure compensated, variable displacement piston pump and closed-center control valves used in a Proportional Priority Pressure Compensated (PPPC) hydraulic system. The PPPC hydraulic system divides the oil flow between each operating circuit in the system. The amount of oil directed to a particular circuit is proportional to the position of the compensator control spool. Because the valves are pressure compensated, cylinder speeds will not change as the load varies as long as the pump can meet system flow needs. When the flow demands of the system exceed the total flow available from the pump, the flow is divided proportionally between all activated circuits; however, the work tools will all move slower due to the reduced amount of flow available. The "A1" solenoid and "A2" solenoid provide pilot oil to shift the control spool for the auxiliary functions. These solenoids are proportionally controlled by the Machine ECM. The operation of the valve is identical to that of the B Series valve, however the high flow selector switch has been removed. The High Flow operation is now contolled by the presence of a High Flow enabled worktool being detected across pins F and G on the worktool electrical connector. The high flow operation functions similar to the "standard flow" circuit, except that the Machine ECM directs more current to the A1 or A2 solenoid valves, allowing the auxiliary control spool to shift farther. When the thumbswitch is in the High Flow mode (maximum UP or DOWN position), higher current is sent to the auxiliary solenoid. This will allow more hydraulic oil flow to the auxiliary hydraulic circuit. A dual stage load sensing relief valve is used to maintain system pressure. The system pressure is increased during high flow operation through the "A1" or "A2" solenoid. When only the high flow circuit is active, the Machine ECM will energize the XPS control solenoid for the dual stage load sensing relief valve. The pressure cut-off spool within the Pump Control Valve will now limit the maximum pressure. The "C+" solenoid and "C-" solenoid provide pilot oil to shift the control spool for suppling oil to the secondary auxiliary lines on the work tool lift arm. The "C+" and "C-" solenoids are ON/OFF and controlled by switches on the work tool joystick Operation of these circuits will cause the XPS control solenoid valve to de-energise, (should pins F and G be shorted together) therefore reducing the max system pressure to the “standard” value. Upon releasing the buttons, the ECM will re-energise the XPS control solenoid valve. NOTE: Although the outer two envelopes on each end of the auxiliary/high flow spool are identical on the schematic, more flow is allowed through the outermost envelopes
I received my pressure test kit today and was able to complete some testing. I think the information I gathered should help in starting to piece together this puzzle. Standby Pressure Test Set gauge on the pump discharge pressure port under the tool control. Fired up the machine and saw 700psi at high idle. Testing procedure calls for 420+-44psi. So this failed by around 65% Margin Pressure Test Unable to preform as I do not have a quick connect jumper for the Aux lines Pilot Pressure Test Connected gauge to the pilot pressure port. Access to the charge pressure was limited so i figured i would see if the port caused any concerns as it is past the charge port. Pilot gauges read pretty close to spec. 370psi at idle and 440psi at high idle. Spec calls for 399+-29psi and 479+-29psi Load Sensing Pressure Test Connected gauge to the load sensing pressure tap. High idle ran the bucket all the way down. Bottomed out and saw 2800-3000 psi. Spec calls for 3050+-100 so this seemed fairly close. I went outside of the testing procedure and wanted to see what this would do during the bogging event. when bogging the machine with no input to the controls this port saw ~300psi. As soon as i would bumped the controls enough to get the bogging to stop the gauge dropped back to zero. The bogging only happened when this gauge was reading that ~300 psi. Pump Discharge Test Connected gauge to the pump discharge port and ran the bucket all the way down at high idle. Immediately pegged my 4000psi gauge. Swapped for a 10000psi gauge and repeated. Saw 4400psi. This is far out of the spec at 3335+-145psi. This was off by about 32%. I again went outside of the testing procedure and saw this pressure with no input during the bogging event and saw that when it bogged the pressure remained at 4400psi. When the bucket was moved enough to stop the bogging the pressure dropped to zero. I am not sure what to make of these results. The pump discharge being much higher than spec calls is quite strange but the load sensing holding that 300psi during the bogging event is what confuses me. I am not sure how the load sense interacts with the system pressure. But everything else seemed to follow the controls, although pressures were high. Thoughts?
i would remove and cap the signal line and fitting on the valve on the bottom of the pump if the pressure still remains high the pump or the valve on the pump are faulty i have seen the swash plate pivots on these get flat spots and cause all sorts of odd results Mark
You never mentioned anything in your OP, but how did this problem start.? Slowly getting worse over time or literally changed from no problem to problem between one day and the next.?
So looking at the schematic and the explanation you sent removing this line should make the pump only run at standby pressure correct? Since the pump will not see input on the load sense circuit it should not attempt to increase pressure to make up for the flow? I purchased the machine in this state but the previous owner explained that the problem started recently but has gotten much worse within the last week of his ownership. Machine was being used daily.
yes that is what should happen
I got plugs today and capped the line into the pump fired up the machine and saw around 500 psi standby pressure(seems within spec i was using a 6000 psi gauge so there is some uncertainty). Ran the bucket tilt up and down, and saw no bogging. Went to lift the bucket and found that the bucket moved very slowly and stopped around 2 feet off the ground. Went back down with no issues. tried going back up and only got around 18 inches high. back down no problems. Then the bucket could barely move an inch. The entire time the pump discharge was sitting around 500 psi, never bogged or saw anything like the 4400psi from before. I couple spikes(700 psi) when rocking the tilt function but mainly ~500psi the whole time. The bucket raise definitely has an issue based off what I saw. Is it possible that a bad or worn raise solenoid is to blame? Not sure how this would correspond to the load sense spiraling out of control to 4400psi. Thoughts?
I should add also that when running the functions, tilt down, tilt up and lower all could be seen on the pump discharge when initially triggered by a "dip" in the discharge pressure very quickly before the bucket started to move. When raising the bucket this was not seen.
First place I would check is the load sensing relief valve. You had 700 psi getting past this relief valve during the standby pressure test when there should only be 420 psi. We now know the 700 psi isn't backfeeding from the pump control valve. I wonder if the o-rings are worn?
Be aware with the signal line disconnected from the pump. The pump out put should not increase. What you are seeing is pretty normal for a pump on minimum output. The reason to check with signal line disconnected is to make sure that the pump is not delivering high output without a commanded signal from the control valve. Having said that, the swash plate in the pump could hang up due to flat spots on the swash plate pivots and cause problems
I was out of town for a while so I am just getting back to this and getting to work on it. As stated before I do not see the odd jump in discharge pressure with the load sense disconnected. This seems to me that it is possibly an issue with the load sense valve as stated. I am looking at a parts diagram of the load sense valve and from my under standing the adjustment with the smaller spring is for the Margin pressure adjustment and the larger bottom spring is for the High flow pressure adjustment. I am also seeing some pins and orings on the left side labeled "14". Just want to bounce this off you if there is anywhere i should be looking first? It seems like it could be sending the pressure high if the discharge pressure being sent to this valve was getting around the regulating springs and causing issues. I may just start taking it apart and see what i can find.
Is there any reason that the load sense input line coming from the controls would/could be faulty? Just want to make sure i am looking at the right side of this issue.
So during the bogging event with no operator input, you have 300 psi signal pressure and a pump at max displacement. For me that pump is doing what it should be doing. Anyone disagree?
That is correct. It is my understanding of the machine that if there is no input to the controls the pump should not be trying to build this much pressure. So it is possible that the issue is inside of the controls and is sending signal pressure when it should not be? Edit: Confirming question, 300psi signal pressure causes 4400psi pump discharge?
I have an idea that i think might work to help tell what's going on. I plan to leave the load sense input signal disconnected and use a hand hydraulic pump to give this input a little pressure when i try to move the bucket. This should allow me to confirm if it is the hydraulic pump "running away" or if this input signal from the valve body is sending bad pressure. Any reason i wouldn't want to do a test like this? I would of course not send any pressure over the 300psi I see.
During the bogging event, what happens if you move another machine function... does the load sense pressure come back up and bogging corrects itself? That's basically doing the same test as you describe above but using another circuits load sense signal. Can you get to the load sense relief valve I mentioned in post #21 without pulling the implement control valve out?
I will run the controls a bit more tomorrow with the load sense hooked back up and two pressure gauges at the same time to get a better description of what is happening when another function is used. If i am understanding correctly when i run the machine at any given time I should see the pump discharge pressure around 350psi more than the load sense signal pressure. I am going to check on the location of that load sense relief valve, Based on the attachments above i am pretty sure i will be able to access it. Also I dont think i mentioned this but during the bogging event the empty bucket will barely move as if it is attempting to lift too much weight. Not sure if that changes things or not. I still plan to check these pressures.
That's basically it. And that 350 psi is what they call margin pressure. It's controlled by the margin spool in the pump control valve and set/adjusted by changing the margin spool spring compression. Margin pressure in most cases (and in yours) needs to be checked or adjusted while an implement is being moved, hence why the procedure calls for that auxiliary hose that connects and loops around your auxiliary ports. I've had success using the raise command to check margin pressure... the problem with that is you only get 1.5 seconds or so to check your gauges while the boom is between roughly mid way up and full stroke. Not ideal but it does get you in the ballpark.
So I took the machine out yesterday with a fresh mind and a better understanding of the how an axial pump like this works. hooked gauges into the load sense port and the pump discharge port. Fired up the machine and saw that the pump discharge was around 750psi and the load sense was 0psi. Ran the machine around for a bit, worked all controls had had the bogging event regularly. The entire time the machine was operating and not bogging i saw ~750psi of margin pressure. I was able to confirm that at the bogging event the machine would surge the discharge pressure to ~4200psi and when I let go of the controls the load sense would drop to 0psi but the discharge pressure would stay hung up at 4200psi. If i bumped the controls a bit i was able to "knock it loose" and it would go back to normal. I decided to address the margin pressure first as that was adjustable and would start to eliminate causes. This is where it got interesting. I found the margin adjustment on the load sensing valve and went to loosen the set screw, it felt like it was hand tight at best, loosened it about 2 turns and adjusted the valve about 1-1/2 turns(247 psi per turn). which would give me the 350psi margin pressure. I went to tighten the set screw and it took nearly 4 full rotations to tighten it back down. Very odd. I did also notice at this time that the entire pump was painted OEM back, but this load sense valve was rusted like it had been replaced at some point. Hoped in the machine and fired it up. Pump discharge ~350psi, load sense 0psi. Perfect. Ran the machine around and did some digging. Did not bog one time, pressures never got hung up like before. No matter how hard i pushed the machine or tired to get the bogging event to happen it could not do it. The machine ran like a top. I am going to run the machine some more before I call it fixed. But I think that has resolved this issue that i was having. I can only imagine that at some point that load sense valve was replaced or adjusted, and that set screw was not tightened back down correctly. Over time it worked itself higher and higher. This would not really be noticed as it would not slow down the movement or lack power. It kept creeping until the point that the limits of the pump were reached and something was hanging up. My thought currently is that the swash plate was "hyper extended" and the angle created between the swashplate and actuating rod could not be overcome as easily. This would explain the random occurrence and the slow period over which the issue arised. Again I am 98% sure that this issue is fixed but I am 100% sure this troubleshooting would have been much more difficult without your help. Thank you for your quick responses and extremely helpful graphics, procedures, and descriptions. I feel that i have not only fixed my machine but have learned much about the hydraulic system that will be of benefit in the future. Thank you again!