I recently purchased a (2006?) Cat 312CL excavator. Serial # CBA03000. It has 7,000 hours give or take on it. This machine was sold to an equipment sales company by Yancey Brothers Caterpillar when Yancey was selling off part of their demo fleet a couple months ago and then I bought it from the equipment sales company. EVERYTHING on this machine seems to be in tip top condition except now that its on job sites, it feels weak. I have had Yancey pull service records for me and by the looks of things, they kept this machine serviced religiously. The issue I'm having with this excavator is it seems pretty weak under any sort of load. As long as you are operating in mid air or under no load, it is very fast and very smooth, but doesn't perform well under loads. For example: I can grab a 5 inch tree that is 20 ft long on the end and try to swing and the machine wont budge it, but will swing it once I grab it in the middle and its balanced perfectly. Turn right around and I can pick up a 20 inch tree that is cut 20ft long and it will swing it once its balanced perfectly in the middle. The machine will also not dig a full bucket of dirt at once. I constantly have to cut away at it about a half bucket at a time. It will not shove hardly any amount of debris or dirt with the bucket either. Overall it just seems weak, but yet is still fast when not under any sort of load. Spins quick, curls quick, booms in and out quick, and tracks quick. I have operated several smaller excavators that seem much stronger than this one, but I have heard lots of great things about a cat 312cl for a while now, which is why I bought one. To add, the motor on this thing does not bog down at all and runs very well so we can rule out any issues on the fuel and motor side. And also it operates the same whether you run it for 20 minutes or 10 hours, the weakness doesn't change. I do not have gauges to check the hydraulic pressure, but am hoping someone could point me in the right direction of what could be going on with this thing or maybe tell me how to increase the pressure or flow of it. Thanks for any input yall may have!
Before going any further, do you have an Operation & Maintenance Manual for it.? Some of these models have more operator-variable adjustments than you can shake a stick at. Probably the best $50 you might ever spend. I can look up the reference and get back to you.
Yes, I do have one. It came with the excavator when I purchased it. I just ordered a complete service manual for it today as well.
Just for an update. I looked around in the operation manual and didn't find anything really related to any sort of adjustments like this. Thanks
Hi, If you know how to enter the machine's data mode then find out whether engine rpm signal is there. If the speed sensor failed then this kind of thing can happen. And need to check the condition of the PRV solenoide & signal to it from the controller as well. First check whether speed sensor is working or not.
Hi, I can see the engine's RPM signal in the system. I found this the other day when I was cycling through the system service settings to see if maybe someone before me had the computer set on an auxiliary tool or something of the sort, which unfortunately was not the case. Now as far as the PRV solenoid, how do I check the condition & signal of it? and do you by chance know where it would be located on this particular machine? I haven't received my service manual in the mail yet, and probably won't for about a week or so, so I'm currently a little lost on all the locations and testing procedures of this stuff. Thanks for your help. EDIT: I'm assuming we are talking about the Pilot Relief Valve, which for this particular machine should be Cat part # 215-4909. If this is the correct valve that we are talking about then I know it is located on the filter housing of the filter # 5I-8670. If this is all correct, I guess I would just need to know how to check the condition and signal of it.
Hi, No this is not the one i am reffering. PRV means proportional reducing valve and it is normally situated in the pilot manifold. I will serch and post a picture of it with some details.
Awesome! Thank you so much
You can find the location of PRV by reffering the image attached. And turn off the start key and disconnect the prv connector near the prv solenoide and check the resistance of the solenoide coli by using a multimeter and it should be 9 - 15 ohms. And check whether is it shorted inside by checking the continuity by placing one probe to the solenoide body where is free from paint. If those checks are ok then we can move in to check the availability of controller signal to prv. One thing, see whether your pump backup switch is in the auto position if it is placed to manual position changed it to auto positon and check the machines operation. If it is already in the auto position place it to manual position and use the toggle switch near the back up switch to control the governor and see how the machine works and find out that any changes happens.
Sorry for the late reply. I believe I have found the correct part that we're talking about, but I want to confirm with y'all. Is the PRV solenoid Cat Part # 111-9916 on the diagram attached? It's description through Caterpillar states: "Cat® Valve Assembly (Solenoid and Pressure Reducing)"
Hi, Yes this is the correct part number 111-9916 for the PRV solenoid. Before purchasing it do the above mentioned checks on it to confirm whether the part is good or bad.
I will check it and hope that it isn't the issue. Haha! That thing is PRICEY!! Seems like everything with a CAT name on it is on up there though. As far as the part # and diagram, it's just much easier to look at diagram's instead of pictures is some cases, this being one of them. I just wanted to post it for information purposes so someone else could potentially find it easily later down the road if they're having troubles. Hang tight and I'll let you know how everything checks out as soon as I can. Thanks!
First thing I would do is verify it is hitting hi idle. See what it is and compare to what it is supposed to be. Our 320c's have a tendency to stretch the cable and lose RPM's over the years. Adjusting the cable fixes it until the cable eventually breaks and then it gets replaced. I am not sure if the 312 is the same setup but I suspect it is. A few hundred RPM make a huge difference.
Before you start throwing parts at it first check pressures with gauges and check rpm, cycle times will give a good indication of flow. I know a few rental companies here that turn down the main relief pressure when they take delivery of a new machine. Maybe the rental company that had yours done the same.
Alright, here is some updated information for y'all. The PRV solenoid's resistance is 13.3 Ohms. There is no short in the solenoid. The backup switch was originally set in "Auto" - I switched it to manual, maxed out the RPM's, and had no change in hydraulic performance. While I was in the cab, I logged into the system to pull a little more information off the computer. Just to confirm, there are no active codes. My idle speeds are as followed: #1 - 831 RPM's #2 - 1053 RPM's #3 - 1272 RPM's #4 - 1385 RPM's #5 - 1549 RPM's #6 - 1752 RPM's #7 - 1888 RPM's #8 - I guess I missed that one #9 - 2004 RPM's #10 - 2209 RPM's While in the system, I pulled up the Service - Calibration - PS PRV - Low & High. The low was set to +12 & the high was set to +2. Not exactly sure what that means. Was hoping one of y'all could explain that to me please? I also pulled some more information from the system screen under "Machine Info" while idling at #10, "IMPL PUMP (D)" pressure - 4600 KPA - while idling, not moving joy stick. "IMPL PUMP (D)" pressure - 23700 KPA - while lifting the boom "IMPL PUMP (I)" pressure - 5400 KPA - while idling "IMPL PUMP PWR SHIFT" pressure - 2528 KPA - while idling Again, not sure if any of this will help or not. If its useless information, feel free to tell me! Haha
Hi, It seems prv is good. Now if you can turn off start key & reconnect the prv connector & check the supply voltage signal level to the prv solenoide from the controller after turning on the start key.( back up switch must be in the auto position) To do this if you have not correct tools you have to pierce the two supply wires to prv near the prv. But make sure not to get shorted both together or to the machines body. And the voltage level should be 6 - 9 dc volts. And when the machine starts and control lever operates then the voltage level will drop.
Thanks, I will check that in the morning and let you know what it is. If the voltage checks out good, what would be the next thing that I should check?
it looks as though your engine RPM figures are close to specification. At least it proves the High Idle RPM is being achieved, See attached.
Awesome! I was wondering if the RPM's were where they were supposed to be or not. Thanks for that!
I checked the voltage going to the prv solenoid and it was 15.6 volts before starting & 17.1 volts after starting.
Hi, I hope that you did not disconnect the prv from it's connector while measuring voltages. If it is yes, then this might be the problem for your machine's weak feeling. Because this voltage level should be with in 6 - 9 dcv. If it is around 15 -17 volts means too much current for the prv solenoide. Because of that prv will send high power shift pressure all the time to the pump regulators which will reduce the angle of the swash plate all the time which will reduce the flow rate. Because of this when you work, machine will slow down very quickly with the load. Because angle of the swash plate will control by the combination of internal pressure of the pump and with the power shift pressure that comes from prv. Here what happens power shift pressure is always high from the prv. So now less internal pressure will need to reduce the angle of the swash plate. Because of this comparing to normal conditions when your machine operate with some load machine will slow down quickly due to the high power shift pressure. I think this will be a controller broblem. But before come to a conclusion we have to check the wiring lines for the prv to find out whether are there any shorts. As you checked voltage earlier to the prv, now place the back up switch to the manual position and measure the voltage again. Is there any different from ealier reading. After that again check the voltage between the A769 Gray colour wire of the prv with the body ground when key switch on and back up switch at auto position. And voltage should be 0 volts. If you check the wiring these two wires goes to the back up switch. From there when you place the back up switch to the auto position then these two wires connects with two wires that comes from controller. A769 gray colour wire connects with L968 orange colour wire. A768 Blue colour wire connects with L969 White colour wire. These are the wires you should check whether are there any short circuits presents or continuity exists. If you do the continuity check switch off the disconnect switch and key switch before doing that. If you need i will send the wiring diagram to you.
Hi, When you take this voltage reading was the back up switch on auto position ? If not place it to the auto position and take the reading again.
It was in the auto position, but I completely didn't catch the part where you said to pierce the wire. I just unhooked the connector from the PRV and grabbed the voltage from the connector itself. Sorry about that. I'll skin the wire a little and check it again in the morning. I will check it in both Auto and Manual mode. I will also check for shorts while I'm in there as well to rule that out. Once that is complete, what should be the next thing I check if everything on the PRV checks out to be okay? Also, thank you again for all of your help. It is greatly appreciated!
Hi, If the prv supply voltage with in the specifications that means 6 -9volts dc then that means prv solenoide works fine. But there is prv sweep test to do to exactly confirm that by entering to machine's data mode. But you will need a pressure gauge to perform it. Next we can recalibrate the prv using machine's calibration mode to see whether it will solve the issue. But again you will need a pressure gauge to perform it correctly. We can calibrate it without a pressure gauge as well but that is not recomended.
If you can find out the pressure readings of bucket in, out arm in, out etc. Move the control lever to its full stroke until pressure rises to its release point and then note the max pressure readings on the monitor.
Okay, awesome! I certainly will check all of that and let you know what it is. (Just to add to the quote above) I was messing with it again earlier today and on the "IMPL PUMP PWR SHIFT" pressure reading, it was still 2528 KPA while idling, but dropped down to around 750 KPA as soon as I tracked the machine forward or anything to do with the hydraulics. My calibration readings for the "PS PRV - Low" are +12 and "PS PRV - High" are +2. Not sure if that's any help as well or if that is even close to where it is suppose to be but figured I would throw that in there as well to see if it helps. But overall, I will most definitely get the accurate readings of the PRV voltage for you, will make sure it isn't shorted out anywhere, and will get all of the pressure readings to you as soon as I can in the morning.
Hi, I asked you to see at the pressure readings because as "Kobelco ireland" said this may be a thing we should look at as well. I think this reduction of power shift pressure is happens as it should be. Because at idle swash plate angle kept at a minimum angle to reduce the flow rate. ( hence power shift pressure is high) But when implements or tracks start to work it will monitor by the pressure switches at the main control valve and send that signal to the controller and then controller will decrease the out put voltage level to a certain point and it will reduce the current to the prv solenoide therefore power shift pressure also will decrease and it allows the swash plate to increase its angle to provide required flowrate. Next time put the machine to high idle and operate the control lever to its full stroke on bucket, arm in and out until pressure increases to its release point and then note the power shift pressure at that point, at that moment power shift pressure should be at its highest. But i am not sure whether above readings you mentioned are the correct pressure readings. I will check on that. If these readings are ok then it means prv is working correctly. So 1.check the voltage level correctly at the prv when key swich at on position and start the machine and operate the stick out until pressure reaches to its release point and note the voltage level at that moment also.(should be with in 6-9 volts.) 2.check the pressure readings on the monitor when you operate implements in and out to reache to its highest pressre until release and note the each pressure values. By doing this we can get an idea of whether relief valves have been adjusted.
Hi, here's some information. Key on at prv, 7.1vdc Engine running while operating control is 5.1 to 5.6 full lift. Impl pump (D) pressure- 5100 KPA at idle - Bucket in - 6600 KPA Bucket out - 15,900 KPA Boom up 16,000 KPA Boom down - 17,400 KPA Stick out - 17,000 - 18,000 KPA Stick out - 16,600 KPA Forward tracking 9,400 KPA Reverse tracking 10,100 KPA. Imp pump pwr shift pressure Idle - 2528 KPA Bucket in - 977 KPA Bucket out - 977 KPA Boom up - 1300 KPA Boom down - 977 KPA Stick in - 977 KPA Stick out - 977 KPA Swing left and right both - 977 KPA
Hi, when you take these readings did you operate the control lever to its full stroke until pressure build up to its release point ?
Yes I did.
Hi, It seems to me you have to check the main relief valve relief pressure settings. Because as an example if bucket closes until pressure build up to release point that pressure setting should be around 29900 kpa. So i think it is worth to check main relief valve pressure settings. To do this you will need a pressure gauge and i will send you some informations regarding this.
Hey everyone. I hate leaving a thread wide open like this so just wanted to post an update on the machine in case anyone else ever is having issues like mine. I changed all of the hydraulic fluid and filters and it seems to have fixed the weakness. There were some small pieces of sponge like foam caught in the return filter so I suspect that that may have had something to do with it being a little weak as well, but now it seems to be doing fine and has been working all day every day for the last couple of months and has been great. Thanks very much for all of y'alls help. It was great appreciated.
Just to clear up a misconception... That is not true. The protocol on these machines (Caterpillar) is to maintain target engine rpm, period .... so, in order to do so, the pumps get destroked as needed in order for the engine to not fall below target rpm. A poor performing engine (say restricted fuel filter) will still maintain proper rpm, even it means full destroking of the pump(s). Only after full destroking of the pumps can the engine rpms falter if the hydraulic load is still too high for an engine with a performance issue.