Cat 320CL low hydraulic power

[gcsupraman]

Hello.

A few weeks ago I purchased a Cat 320CL which is my first piece of heavy equipment.

I used it for the first time today and the hydraulics seems weak. I can scoop a full load of dirt but it’s very slow. Same with raising the boom and loading a dump truck - very slow. It’s like the engine is on level 8 speed and the hydraulics are on 4. The engine doesn’t stall and otherwise the machine seems to run great.

I tried to do some reading on the job site and I don’t believe the hydraulic pressure adjustable. Any ideas on where to start?

I’ve owned mini excavators for several years but nothing this size so I apologize for this basic question

Serial number PAB03299

Thanks

 

[gcsupraman]

I made a video today.

It was a little hard to hold the phone at the same time but there is barely enough power to dig a full scoop of dirt. If I hit a boulder digging with my cat 305.5 it would drag the mini - the 320cl didn’t move. It picks up a full scoop of dirt very slowly.

The machine only has about 3600hrs on it

 

[digger_hunter]

could be a range of issues. main culprit would be the pressure switches. you can try this first, open the right side armrest and switch to manual mode (display switches off I believe) and see if the machine is operating quicker.

if it doesn't help the power of the machine I think the issue is a faulty main relief valve. there's a few things you an do to diagnose further and even fix it by tweaking the main relief valve. But better take it step by step as I think you have a easy fix for the issue. PM me if you need any diagrams etc

 

[gcsupraman]

could be a range of issues. main culprit would be the pressure switches. you can try this first, open the right side armrest and switch to manual mode (display switches off I believe) and see if the machine is operating quicker.

if it doesn't help the power of the machine I think the issue is a faulty main relief valve. there's a few things you an do to diagnose further and even fix it by tweaking the main relief valve. But better take it step by step as I think you have a easy fix for the issue. PM me if you need any diagrams etc

Thank you for the response.

Unfortunately I scheduled field service with the local Caterpillar dealer and they were out this morning at 8am.

After 2 hours of diagnosis they are claiming that the machine is operating normal ‍♂️. I believe they said the pump pressure was holding at around 5000psi. They claimed the PRV valve could be intermittently sticking - but nothing was done since they weren’t able to find anything obvious.

I will run the machine a little more next week and circle back

 

[digger_hunter]

So I reckon the problem is that the pumps are developing pressure but not flow, hence the reason its so slow. Depending if the entire system is slow or just some functions you can eliminate certain problems. In your case I think its the whole system that's slow?

Main relief valve: usually when this gives up the machine ends up being slow as the flow just goes straight to the tank from the control valve, you could try adjusting it but just mark where it was originally if you don't have a pressure test gauge

Faulty pump pressure sensor: one of the 2 or both pump high pressure sensors could be faulty

If the pressure develops and then dies after a second or less could be faulty regulators, we have seen that a lot with the C/D range of Cats

You can go into diagnostics from the monitor and eliminate a lot of the issues, even read the pressure signals etc. So better do that methodically and you can trace it to the fault. Let me know if you need the manuals or any help just PM me. The code for getting into the SERVICE MODE is FFF1 or FFF2.

Good luck!

 

[gcsupraman]

I just wanted to post an update in case others are having the same problem.

Digger hunter has been helping me diagnose this issue and I think we have made some progress towards identifying the issue.

The machine seems to be generating proper pressure as displayed in the service menu. At least the pressure switch thinks so

On engine speed 9+ the machine runs perfect, it’s only in lower speeds the machine has very low power. The decrease in power is not lineal. On the 330cl at work and I’m my 305.5 I can do everything I need on level 6 or 7. On the 320cl it will hardly dig dirt on the same setting. I did discover that in manual mode the machine has noticeably more power so it was suspected that there is the issue with the PRV valve.

The settings of the PRV valve were adjusted in the monitor to see if there were changes in performance. At +30 low and + 30 high the machine would barely move (as expected). At -30 / -30 it was a huge improvement. I am however surprised that the machine is not stalling at the maximum setting so I suspect there could be another issue

I purchased some gauges to do some testing and will update soon.

 

[gcsupraman]

I was able to hook up the pressure gauge today and double check pressures. The PRV valve seems to be working. I can see a real time change in the PRV low and high pressures when adjusting the calibration.

I have confirmed with the gauge that the machine is generating ~5200 PSI of pressure - even in level 6 - so I'm assuming it's a flow issue.

What controls the hydraulic flow of the machine in slower speed settings and how can I validate it's working correctly?

 

[92U 3406]

I believe it is possible to tune the pumps but its been such a long time since I've done it I couldn't possibly trust myself to give you the proper info. I seem to recall it involves setting the margin pressures using gauges and a flowmeter.

 

[gcsupraman]

That’s actually helpful.

Most likely the Caterpillar dealer will be returning to attempt to figure out what the issue is.

I could suggest they look into it that

 

[John C.]

On Cat C series mid size excavators the hydraulic output of the pumps have a programmed output based on engine speed up to level 9 on the throttle dial. In throttle level 10 the hydraulic system is load sensing where the output of the pumps is matched to the RPM levels of the engine as the machine is operating.

As I recall there is a process in the diagnostics of the onboard computer to calibrate the engine throttle control to the throttle dial and then another procedure to calibrate the PRV. I don't have enough experience on these machines to tell you how that is done but if you bring out the Cat people again, I would make sure to bring it up with them and then to stand there and make sure they actually do it.

 

[gcsupraman]

John.

I was able to calibrate the PRV but I was not aware of the throttle dial calibration.

There definitely seems to be a flow issue. I was convinced it was the PRV but now I'm not so sure as it appears to be working.

Pump pressure is good at any engine speed. Maybe the pump flow can be increased or maybe you are correct and a calibration will resolve the issue. I really need to get a service manual for this machine.

Here is level 7 loading loose dirt....raising and swinging was at full speed.

 

[gcsupraman]

The dealer is sending the tech back out on next Tuesday to diagnose the machine further.

Based on comments above, I am going to ask the mobile repair tech to check/test the following:
1. Faulty Main relief valve
2. Faulty pump pressure sensor. (I just went to order one in an attempt to "throw some parts at it" and discovered they are $919 each)
3. "Tune" the pumps using a flow meter.
4. Calibrate the engine throttle control to the throttle dial
5. Pump Controller? This was a suggestion by an in house repair tech at the CAT dealer.

The machine easily generates full pressure at lower RPMS so it seems like a flow issue. The PRV seems to be functioning.

If there are any other issues which would cause significantly reduced flow at lower RPMS please let me know.

 

[JPV]

One thing I would check is the engine speed sensor that is screwed into the bell housing under the muffler. It can pick up metal filings off the ring gear and foul up the signal the computer needs to tune the pump to the motor to keep the motor running at a constant rpm. It will basically default to a low flow condition. Unscrew it, clean it, run it in until it touches the ring gear then back it out 5/8ths of a turn and try that. I have seen that be the problem you describe before.

 

[gcsupraman]

One thing I would check is the engine speed sensor that is screwed into the bell housing under the muffler. It can pick up metal filings off the ring gear and foul up the signal the computer needs to tune the pump to the motor to keep the motor running at a constant rpm. It will basically default to a low flow condition. Unscrew it, clean it, run it in until it touches the ring gear then back it out 5/8ths of a turn and try that. I have seen that be the problem you describe before.

Thank you for the suggestion.

That looks like something that would be easy to check - I’m on it.

 

[JPV]

After thinking about it that could only affect it when the throttle is at 10. I don't know if it affects it at lower throttle settings. Will be curious to hear.

 

[fastline]

Thank you for the suggestion.

That looks like something that would be easy to check - I’m on it.

To clarify, the speed sensor issue will be easily confirmed both in the diagnostic codes and a 0 form engine speed in the diagnostic screen in the monitor. If it is reading realistic RPM, it is probably fine.

You need to run all your diagnostic codes. I suspect your "tech" is more or less a quack if he thinks that is 'normal'. Don't pay that bill!

Your pumps are not up-stroking. If you are not familiar, the pumps are variable displacement and there is an electric servo that controls the swash plates thus the volume the pumps put out. You need to implore that your tech investigate servo positions and recalibrate if needed. What I suspect if they are not doing a damn thing so the only increase you might get is just the RPM bump. Basically running on idle flowrates, just with higher RPM.

 

[digger_hunter]

Hey,
Just make sure you check these out if the dealer is coming out.
-Governor/stepper motor calibration (you can do this yourself pretty easy) from what you have already done this should be ok so just a check of the RPM from display monitor should suffice
-Check Negative Control pressure from MCV to pump is ok, it should go to zero when you operate any implement fully. This is what increases pump stroke and there's one for each pump going from each half of the MCV. Would be interesting to see if the pressure is dropping but pumps flow is not increasing. We have seen SBS80 pumps with the regulator arm spinning back so could be that. However haven't see a SBS120 on a 320C do that yet! If its has gone back then the stroke angle would be reduced quite a lot and that could be a an issue.
-Check current at PRV is within spec, should be between 0.1-1.0amps from idle to when pumps are being relieved

Hopefully they sort you out this time!

 

[Mobiltech]

From all your testing and the video I would doubt very much that it is a main relief problem. You say the pressure is good at all speeds so if it was a relief problem you should see a drop in pressure at low rpm.
I would definitely be looking at negative flow control settings and also pump control head adjustments.
I didn’t see any mention of pilot pressure testing at all rpms. That could also be an issue if it’s dropping off at lower rpm.
I would also do a track speed test to see if both are equal to rule out one pump being weaker.

 

[fastline]

From all your testing and the video I would doubt very much that it is a main relief problem. You say the pressure is good at all speeds so if it was a relief problem you should see a drop in pressure at low rpm.
I would definitely be looking at negative flow control settings and also pump control head adjustments.
I didn’t see any mention of pilot pressure testing at all rpms. That could also be an issue if it’s dropping off at lower rpm.
I would also do a track speed test to see if both are equal to rule out one pump being weaker.

This is something I meant to mention and it should be checked! Weak pilot pressure will not allow main spools to move as they should even if you are applying full stick. What I would probably do is select one side of one spool on the main valve block, command that function with full stick, and verify full pilot pressure is there. Sort of checking the pump, relief, etc, all at the same time.

 

[gcsupraman]

To clarify, the speed sensor issue will be easily confirmed both in the diagnostic codes and a 0 form engine speed in the diagnostic screen in the monitor. If it is reading realistic RPM, it is probably fine.

You need to run all your diagnostic codes. I suspect your "tech" is more or less a quack if he thinks that is 'normal'. Don't pay that bill!

Your pumps are not up-stroking. If you are not familiar, the pumps are variable displacement and there is an electric servo that controls the swash plates thus the volume the pumps put out. You need to implore that your tech investigate servo positions and recalibrate if needed. What I suspect if they are not doing a damn thing so the only increase you might get is just the RPM bump. Basically running on idle flowrates, just with higher RPM.

I was able to go into the diagnostic screen and I did see RPMS which looked realistic to me. There were no fault codes detected so maybe I'll suggest the speed sensor if the other items check out. Or maybe i'll just clean it myself while he's working on other things. Unfortunately the $1500 bill was paid. They took my credit card prior to coming. I basically paid $1500 for 3 hours of the tech checking pump pressures. He did fix the thumb at least

I'm trying my best to keep up with you guys but I'm out of my comfort zone with heavy equipment repairs. I'm going to add your suggestion about the servo positions / calibrations and show this to the tech on Tuesday. I really appreciate the suggestion.