My 320l Cat digger is stalling under load .

[Cat_man320]

My 320l 9kk model was working excellent the last few years. However last week I went to do some digging and under load the engine stalls . I changed the filters and no difference . I then checked the turbo as there was some black smoke as it stalled , turbo didn't spin as freely as i would like so i installed a new one .
same problem , to me it feels like the pilot controls are telling the hydraulic pump to go full pressure and then stalls the engine .
Is this problem common with excavators. really don't know where to turn and desperate . Cheaper to sell machine then to get dealer service call.
I don't have a hydraulic service manual , I know the main pump pressure is 4980 psi and pilot system is 600psi .
The pump control unit is showing normal green light so that must be ok . the main pump must be being stroked too much and hence stalls the engine .
Any ideas ?

 

[Bob/Ont]

It sounds to me like the PRV solinoid has failed or become disconnected. Or as another guy on here recently found a wire to the engine speed sensor was broken.
Look your wireing connections over carefully, especially any place repairs have been done or you have powerwashed.
The the speed sensor tells the computer how fast the engine is turning, when you work the machine the computer looks for a Target RPM and sends a signal to the PRV solinoid which adjusts the Powershift pressure to the pumps. The Powershift pressure plus System Pressure destroke the pump to keep the engine at Target RPM.
Later Bob

 

[Cat_man320]

Where would the PRV solinoid be ? PRV stands for ?? There are no sols or wires on my main pump , however there is a hydraulic block with several sols and hyd. lines going to it and two or three lines going to the main pump.

 

[Bob/Ont]

Where would the PRV solinoid be ? PRV stands for ?? There are no sols or wires on my main pump , however there is a hydraulic block with several sols and hyd. lines going to it and two or three lines going to the main pump.

PRV Proportional Reducing Valve and it's on that block you mention. One of the small lines going from the block to the pump is Powershift pressure and serves both pumps equally. There should be two more lines coming from each end of the main valve and going to the pump feeding that half of the valve. These lines are the NFC lines Negative Flow Control and tell their respective pump when a circuit is activated and flow is needed.
Later Bob

 

[Cat_man320]

Jeeze Thank -you Bob wish I knew as much as you do about this system . So do my 320 have two pumps in that housing. There is a high pressure line on top and one on the bottom of the pump housing and those two go to my control valve body. What kind of voltages would be on those sols on the block( manifold). and when should those be opening and closing ? I don't have a service manual so I'm just flying in the fog . really appreciate your time and info .

 

[Bob/Ont]

The power is low and variable, controled by the computer to provide the needed PS pressure to control pump flow and keep engine RPM on target(around full load) reguardless of system pressure. The solinoids are calibrated by adjusting PS pressure at two points. Need instructions to make computer sweep the pressure and then set the two adjustment points. What's your serial#?
Later Bob

 

[Lee-online]

A quick way to test the PRV is to use the monitor and do a sweep test. Stall the pumps one at a time and listen to the engine. You will hear a nice smooth fluctuation in rpm as it sweeps.

 

[Cat_man320]

The prefix is 9KK, don't have the # right at hand . I wish I had some pics so I would know what valve is what and what each sol does .

 

[Lee-online]

Start with the basics, The fuel system is the first to check but you did that. Did you clean the screen on the transfer pump? The speed sensor is also something to check. Remove it and clean it. Install it by screwing in by hand until it touches the flywheel then back it off 1/2-3/4 turn.

The screen is in the banjo bolt where the fuel enters the pump.



Here is where the speed sensor is located. It is good practice to clean them every so often because they catch the metal that wears off the starter and ring gear.

 

[Cat_man320]

Thanks for the pics Lee, So if the speed sensor was dirty as you say , would that cause the engine to be pulled down on its knees ? The engine runs fine in all positions on throttle range selector . I don't think its a lack of engine power , but its really hard to decipher. If the little screen in the lift pump was plugged, would the engine still give off black smoke as it begins to stall . I can keep the engine from stalling by quickly releasing the load on the joy sticks or letting the sticks go to neutral I will check that tommorrow and inspect that little screen in the lift pump

 

[Bob/Ont]

If the fuel screen was clogged you would likely starve for fuel and not have black smoke.
More likely have an ECM issue like bad signal from speed sensor or PRV signal out of calibration.
Later Bob

 

[Cat_man320]

Thanks again Bob for the reply, going to check speed sensor tommorrow and will check fuel screen for the hell of it .

 

[Lee-online]

ah, I forgot about the black smoke.

I assume your air filters are clean enough?

 

[Cat_man320]

Ser# is 9KK 01222. I pulled off the inlet at the turbo just to make sure . i removed the speed sensor and cleaned it . it was full of what looked like gray grease. screwed it back in until it touched the crank and then backed off about 1/2 turn . still the same . the engine will die if i don't let off on the sticks. still haven't checked the littel screen in the lift pump . its a bitch to get at and it was only 0* this morning and windy at 7:00 AM . hands were frozen .

 

[dirtdobber1]

Cat man,

Take a look at this thread: cat 312 BL hyd problem. You will have to search for it because I'm not smart enough to link you to it. Although it's for a different machine, it contains instructions from Jerimiah Sr on how to adjust the PRV solenoid to isolate it as the potential problem. I was having the same problem with my 312, and it was the PRV solenoid ($100 part from Cat). This adjustment is quick and easy, but be cautious as I have no idea how much the systems changed from the 312 to the 320. Good luck.

 

[d9gdon]

Cat man,

Take a look at this thread: cat 312 BL hyd problem. You will have to search for it because I'm not smart enough to link you to it. Although it's for a different machine, it contains instructions from Jerimiah Sr on how to adjust the PRV solenoid to isolate it as the potential problem. I was having the same problem with my 312, and it was the PRV solenoid ($100 part from Cat). This adjustment is quick and easy, but be cautious as I have no idea how much the systems changed from the 312 to the 320. Good luck.

This one:

https://www.heavyequipmentforums.co...-hyd-problem&highlight=cat+312+BL+hyd+problem

 

[Cat_man320]

Well It looks like I may have found the problem . The is a mode switch in the joy stick housing just under where your left elbow would be . i slid off the cover and the switch was in limp mode or the "turtle position" I switched it to auto and tried the digger and it seems to work as normal . how the switch got to limp mode , i have no idea. I have never had the cover off since I bought it but there were signs that somebody switched it as there was dust disturbed on the name plate. My machine is locked everytime i leave it with power disconnect off and side panel locked also . Somebody must have gotten into it (Cat keys are everywhere) and switched it. Thats the only scenario I can come up with . It was working fine one day and not the next. somebody had to know where the switch was plus the result of switching the switch. No a very nice trick to play, cost me a new turbo plus unnecessary filter change, plus four or five days work. there's no way the switch could change on it own. i'm not happy with the situation but glad I can get back to work to make a living .
My only question now " is "auto" the correct position for the toggle switch?

 

[Bob/Ont]

Yes, the limp home mode is a manual mode to limp the machine to safety. Low power not meant for working.
Later Bob

 

[Cat_man320]

Yes Bob, so would that be why the machine would be stalling in that mode . Now I wonder if the switch is hooked up the right way. I tried the digger in auto mode this morning and it seems to run great.

 

[Cat_man320]

WELL IT LOOKS LIKE MY PROBLEM IS NOT FIXED . THE MACHINE WORKS OK IN THE AUTO MODE BUT IS SLOW , WHEN I GO TO THE LIMP MODE (TURTLE ) the machine speeds up but will stall when i induce a load . So I'm wondering if the wires on the switch is crossed. I wish i knew what sol was the PRV one . I would change it. So back to sq. one.