Cat excavator periodic slow hydraulics

[Columbo]

I’ve noticed a strange, periodically reoccurring issue with my excavator- Cat 311B s/n 8GR00401. Sometimes after I’ve been running for awhile the hydraulic functions will slow down. The problem primarily effects the boom/stick/bucket circuits and not the slew/travel functions. It seems to vary on run time before it occurs- I’m not sure if it’s temperature related but today the hydraulic oil temp gauge was at 3-4 bars when it happened. (The oil has never been over 4 bars on the gauge). The machine is usable, but noticeably slow, when the problem happens. If I keep working the problem will eventually stop and the hydraulic functions return to operating normally.

Today when the hydraulics slowed I switched to manual mode and it seemed to “fix” the problem. After running for a few minutes in manual mode I switched it back to auto and the problem did not reoccur. There are no stored codes. Any thoughts on what could be happening and how to troubleshoot it from here?

 

[Welder Dave]

A sticking sensor or something along those lines?

 

[Columbo]

That’s a possibility, I’m just not sure which one?

Mods/admin- I mistakenly posted this here instead on the excavator section. Could you move it please?

 

[Columbo]

Bumping this back up- I ran the machine for several hours yesterday loading trucks, no heavy digging. When I first noted the slow hydraulics it also appears that the engine tone changed, almost like it decreased in rpm. The hydraulic oil gauge was at 4 bars at the time. After I finished loading the truck I shut the machine down for a while (about an hour) and when I resumed working it operates normally. I checked the fault codes at the end of the day and there were no stored codes that would point towards the problem.

Any suggestions for the next steps to diagnose this issue?

 

[zaccolligan]

Put a gauge in your pilot pressure see if its within spec, but id start with replacing your return and pilot filter. Id also check your main relief, it could be getting stuck open once getting abit warm. Put a gauge in the line when it faults and check what your main releif pressure is compared to when its cold

 

[Columbo]

Put a gauge in your pilot pressure see if it’s within spec, but id start with replacing your return and pilot filter. Id also check your main relief, it could be getting stuck open once getting abit warm. Put a gauge in the line when it faults and check what your main releif pressure is compared to when its cold

Ok, that sounds like a good place to start. Would you have instructions from the service manual on where to check the pilot and main relief pressures? And also what the specs are for each? Thanks!

 

[zaccolligan]

On the joystick circuit u will have a P hose thats your primary pilot pressure. Check thats not dropping when getting hot first. Then you can put the guage in before your primary overload releif and see if its getting stuck, but if its only on tour joystick circuit and nothing else its most likely not that. Id start with that primary pilot pressure to the joystick valve.

 

[zaccolligan]

I dont have access to cat manuals only hitachi manuals

 

[Columbo]

So, I have not had a chance to do any further diagnostics with this machine but my brother ran it today on another project and noted the same issue. He agreed that when the problem first appears it sounds as if the engine rpm deceased about the same as one click on the throttle control. As I had observed he also found that after he continued to use the machine for an additional 30-40 mins the rpm’s seemed to recover and the problem resolved.

Does this information indicate anything for diagnosing this issue?

 

[fastline]

Sounds more like you have engine stuff rather than hydro stuff. Remember that with load sensing equipment, they are designed to slow down to match engine output. I suggest you change your fuel filter asap and check that entire area as well as change your air filter. report back. This does not sound hydro related.

 

[Columbo]

I agree that it feels like an engine or engine control issue. New fuel filter last weekend, air filter is clean. The part that really puzzled me is how the problem (slower engine/hydraulics) will resolve if you continue to run it for awhile. The engine still sounds smooth when it occurs and there is still enough power to work, the cycle times are all longer though.

 

[Nige]

Regarding the fuel system have you drained the tank of water & sediment recently.?
Checked that the tank cap is breathing correctly.?
Blown out the fuel lines.?
Disassembled the head of each fuel filter and blown out all the passages with air or run a wire through them.?

You could tell if the problem is fuel-related by temporarily plumbing a pressure gauge into the fuel system and mounting it in the cab. Does the fuel pressure drop at the same time as the machine performance dips.?

 

[Columbo]

Regarding the fuel system have you drained the tank of water & sediment recently.? Yes!
Checked that the tank cap is breathing correctly.?
Blown out the fuel lines.? No, I haven’t tried this, I suppose when the problem starts I could open the fuel cap and see if it clears immediately?

Disassembled the head of each fuel filter and blown out all the passages with air or run a wire through them.? Nope, I haven’t done that either.

You could tell if the problem is fuel-related by temporarily plumbing a pressure gauge into the fuel system and mounting it in the cab. Does the fuel pressure drop at the same time as the machine performance dips.? Good idea, where would you suggest I T into the fuel line?

@Nige I added responses to your questions above. To you this sounds like a potential fuel issue? Would it still run smoothly with the fuel restricted? Thanks for your advice!

 

[Nige]

To you this sounds like a potential fuel issue?

Not necessarily. However to do the diagnostics of this problem you have to start somewhere and what I listed above are my suggestions regarding what you could do (that you haven’t up to now) to eliminate the fuel system as a potential suspect.

There will likely be a plug on the head of the secondary fuel filter where you can plumb in a gauge.

 

[Columbo]

Sounds good, thanks! I’ll investigate the fuel side of things and keep this thread updated.