Hi all, I've recently had a Cat 317 Serial No. 4M00179 come back from a site where it was stood idle for a couple of years. Upon testing, we found it was struggling to lift the boom and extend the stick under no load at engine idle. With increased revs, it would do it, but slower than it should. We cleaned out the tank, fuel lines, replaced all the fuel filters, got the injector pump and nozzles serviced. Now the engine runs a lot smoother, but it's still got the same issues. On idling, all the operations are extremely slow, and when you put the boom down, it just stops there rather than causing the engine to shut off. It's the same for all the controls. I'm pretty sure it's a hydraulic issue, but I'm not really sure where to start. Any ideas?
Research prv in service manual
I believe the serial number is a 4MM0179 and is likely an A model machine.
Hi, As you explained I think your engine doesn't stall under load. Assuming that it seems to me that there is a problem of hydraulic flow. Lack of flow will slow down the speed of actuators. If we think about the operation of PRV (Proportional Reducing Solenoide Valve ) it will direct the power shift pressure pilot oil to the pump regulators to destrok the pump according to the pwm signal sends from the controller according to the signals that it gathers from 1. Engine speed dial setting. 2. Engine speed sensor. & 3.Pump delivery pressure sensor. And by this operation it will prevent the engine from stalling under loads. If one of these components including PRV is faulty or its wiring circuits are faulty or controller it self is faulty, then engine will stall under load. But I have an experience of over voltage supply to the PRV SOLENOID from the controller due to the problem of the controller and this will destroke the pump unnecessarily causing slow actuator movements. So to check that we should check voltage signal to the PRV Solenoid without disconnecting it from the connector using a multi meter. To check this you will have to pierce the two wires if you don't have the check harness for that. (Standard Voltage level should be 1-11Volts.) when machine runs and all control levers in neutral it should be 6-9 Volts. If the voltage level is much higher than this we can assume that there is a B+ short in the wiring harness or controller is faulty. If the readings are normal then we can eliminate the above mentioned issue. If the main pump has worn-out and if the internal leakages are more then also the flow will be reduced than the normal operation. But before judging that I think there are several things to look at, things like whether the swash plate angle has been reduced by making adjustments from the Adjustment Screws & Etc. I think members who has much more hydraulic knowledge than me will help you to figure this out.
Yes it is as he mentioned it should be a A model one with the above serial number. If it is a A model then the voltage level for the PRV should be 6-6.8 Volts at high idle and all controls in neutral. And If you have a monitor panel switches like this then press the power switch until power mode 3 indicator comes on, If you have a monitor panel like this then press the power switch until power mode 3 indicator comes on & Press work switch until it illuminates highest indicator lights other than the lowest indicator light and see the machine's operation whether there is an improvement.
My bad, the serial no. is 4MM00179. I'll have a look at the PRV solenoid, thanks. Is that the one on the main pump? Unfortunately the monitor display is completely wrecked, it's been that way since we imported the machine from Ireland.
with this serial number it reveals that this is a 317 A model machine as sir John C said. you can identify the prv location by reffering to attached image.
I've just tested the voltage at the PRV solenoid at high idle, and it's about 6-6.2V. When the controls are being operated, at some points it drops down quite sharply, but always recovers to the same level.
It seems like supply voltage signal to PRV from the controller is good. But to check whether it directs correct power shift pressure to the pump regulators, there is a test to do called as "PRV Sweep Test " . But to perform that you should use the monitor panel in order to access the data mode. As well as a pressure gauge & a multimeter is required. As you mentioned if you can't use the monitor, measure the power shift pressure at the power shift pressure port at low idle & high idle. And measure the pilot pressure as well at the pilot pressure port at low idle & high idle as well. And put that results here, then someone will be able to comment on that.
If you need these images will be helpful.
Thank you very much indeed, I'll measure the pressures as soon as I get into work tomorrow. Thanks again.
Would anyone have the hydraulic system T&A specs for this machine? Thanks
You're lucky. It's an old-school machine where the T&A is all in one document instead of about a million separate ones which it would be for a newer machine.
Thanks Nige, much appreciated as always!
Finally got around to working on this excavator again. Powershift pressure at tap 1 is about 20 bar. Pilot pressure at tap 25 is very low, again 20 bar. Adjusting the pilot relief valve both ways makes no difference to the pilot pressure. Before doing this I tried changing out the hydraulic oil for heavier grade 68 to compensate for internal leaks/wear, but it made absolutely no difference. Machine still lacks any semblance of power. Quite stumped at this point, so I'd be grateful for any advice.
Took out the PRV, because the solenoid itself seems to be working fine. Disassembled the valve, and saw the tiny spring at the bottom was completely collapsed. Replaced it with a similar diameter spring, but couldn't really tell the right length to cut it to as the original was completely gone. So I cut it to what I thought would be approximately the right length, put it back in and started up the machine. Pilot pressure went up to about 27 bar from 20 at high idle, and the machine had noticeably more power than before. Then I decided to take it out again, and slightly increase the length of the spring to give me what I thought would be more pilot pressure. On the contrary, pressure dropped back to 20 bar. Put the spring I had cut earlier back in, and again, pressure still at 20 bar. So I had it for a short period, but somehow messed it up. Anyone with any idea on where I could've gone wrong?
hi, if you are able to perform the PRV Sweep Test then you will be able to find whether correct current signal comes to the PRV from the controller & also you can find whether PRV sends the correct PS Pressure to the regulators. if the pilot pressure is below the spec of the pilot pump then first you should correct it before doing above mentioned test. a worn out pilot pump can decrease the pilot pressure and flow and it will reduce the speed and power of all the implements.
Thanks for the info! What's the procedure for doing the sweep test? Thanks
I removed the PRV today morning, cleaned it out and put it back. Bled out all the air from the system, and when I started the machine the pilot pressure was at 34bar at high idle. Tested it and the power was good. Switched it off, started again a few minutes later, and no power again. Measured pilot pressure, it was down to 17bar at high idle. Would this be a relief valve somewhere in the system sticking, or is it a sensor/solenoid issue? Like I mentioned earlier, the cab monitor isn't working, so I can't really access any error codes on that.
What Do you mean here as pitot pressure ? Is it power shift pressure on power shift pressure port or pilot pump pressure at pilot pump pressure port ?
Pilot pressure at the pilot pressure port just about the pilot relief valve.
So bit of an update, excavator is still having the same issues. Measured pump pressure, it’s within spec. I’ve taken the entire control valve block apart twice, checked and adjusted all the relief valves twice, checked all the spools, and still no change. Then I had a power loss issue on a 320D, and the monitor displayed a message saying “low mobility mode”. Turns out someone had flipped the auto/manual switch behind the right hand armrest to manual. When I flipped it back to auto, power was back to normal. So I tried that on this excavator, but there’s no change. So I opened up the panel and measured all 6 wires with a voltmeter, and all of them are at 0V. Does anyone know whether this would cause the issue? Cheers guys
Sounds like computer doesn't have control of prv valve but it's more than that if it doesn't work in manual mode. Manual mode Should send steady power to prv so machine can be operational not as fast as normal but useable
So it’s got a manual throttle control on it, so when we rev up higher, it does have enough power to do a reasonable amount of work. But after a while, say half an hour, it loses power, and you need to increase the throttle further to get consistent power output. I’ve measured pump pressure once it loses power, and it’s still the same as it was on start up.
Pump pressure is how big of a rock you can move. pump flow or volume is how fast you move it. Flow of pumps should decrease as engine feels a load. The prv valve is controlled by computer and it when working properly changes pilot oil pressure going to pump regulators to destroke pumps. In service manual there's theory and operation section which would explain it better. Get a book or download one. Understand the theory then test valve and report back.
Hi, Did you check the pilot pump delivery pressure at the pilot manifold pressure port near the pilot relief valve ? If you didn't check, place the machine on to power mode 3 using monitor pannel power mode selection button and place the engine speed dial to position 10. Turn OFF the AEC switch from the monitor pannel. Bring the hydraulic oil temperature to 50 - 60 celcius by stalling implements several times. Now check the pilot pump delivery pressure at the pilot manifold pressure port. It should be 500 ± 30 psi. As you said, if the power looses after working some time then check the pilot pump pressure at that time also as i mentioned above. Because sometimes if the pilot pump is bad it will looses its delivery pressure when temperature raises.
Makes sense. Any chance anyone would have a copy of the relevant pages in the manual?
Thanks, I’ll check that and revert.
Also, is there any chance anyone would have some diagrams of the relief valves, and their specific components? I feel like someone has taken these apart before me, and fiddled with them, and I think they might be missing either some seals or some circlips. I’ve tried to get blown up pictures on the internet, but no success so far.
Seems like an awful lotta work when u can bump the throttle and “fix” the problem..lol
That’s certainly true. The only issue is that as the machine carries on working, we have to bump up the throttle more and more to get a consistent power output. So I’m worried about engine/pump wear from running at very high rpms for extended periods.
I’ve also been considering something else. I’m running several much older machines on a daily basis, like Cat 12F graders, Champion D-740 graders, Cat 955Ls, an IH TD14A…all purely mechanical. Would it then be feasible to just eliminate the whole PRV system and just run it purely mechanically? Or is it even possible/does it make any sense?
My dad years ago made a plate with a bolt for adjustment to set pump control on a 320 that ECM was bad and customer was tight on funds. It was sort of slow but kept rpms up.
Absolutely brilliant. So that would go on in place of the PRV solenoid? And would tightening the bolt increase or decrease main pump pressure?
I’ve checked the pilot pump pressure, and it’s about 250psi at high idle. Does this indicate an issue with the charge pump?
I’ve tried adjusting the pilot relief valve, but there’s no difference in pressure even if I screw it all the way in.
Hi, That means it doesn't have enough pilot pump delivery pressure. It may be the cause of your problem.
If you can, remove the pilot pump relief valve and disassemble it and see wheather is it good in condition. If the pilot relief valve is faulty or debries stuck in it, then sometimes it will open before the system pressure rises to its intended pressure limit.
I disassembled the valve, but couldn’t find anything especially untoward. Would you have an exploded view of the same, just so I can check all the components are there and arranged properly?
Disassembled the pilot pump, and the top plate on the driven gear side is completely worn (nearly 0.2mm). So currently trying to source a replacement plate or pump.
Any ideas why just one gear would wear the plate and not the other one?