Troubleshooting of Caterpillar 320B Excavator Engine Stalling under Load
2013-07-08
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The common problem of excessive load (engine stalling, lugging) in Caterpillar 320B models typically manifests as a drop of more than 200 rpm under normal working conditions, which is considered stalling.
First, it is necessary to clarify the direction of approach and start checking from simple aspects. Do not complicate the problem from the beginning. (Stalling) is definitely due to a mismatch between engine power and hydraulic pump power. The elimination method is usually adopted, checking mechanical, electrical, and hydraulic systems one by one.
First, a simple engine power check: listen to the sound. At no load and low idle, cut out each cylinder one by one and listen for changes in sound. If there is no change, it indicates the injector is not working (replace or clean). During rapid acceleration, listen to whether the engine sound comes quickly, powerfully, and steadily. If not, check the high-pressure pump, injectors, fuel circuit, intake, valves, and timing. Also observe the smoke color. When stalling, check the degree of black smoke from the exhaust pipe: large, medium, or small. Large may indicate problems with injectors, diesel filter, air filter, or turbocharger. Small may indicate air in the diesel circuit or insufficient fuel supply; check the return oil pressure limiting screw, oil circuit, and gaskets.
Second, electrical circuit. First, set the work mode to boom priority, and set the user mode to U3. Then enter the monitor as follows: on the left, there are four buttons numbered 1, 2, 3, 4 from top to bottom; on the right, four buttons numbered 5, 6, 7, 8 from top to bottom. Press and hold 8 while pressing 3 and 4 for a few seconds until the display shows (00 00 00). First enter the password (0E323A): 1 is to increase the number, 2 is to decrease, 3 is to move the blinking character right, 4 is to move left. After entering, the display shows (10---1). Adjust to 12 to check whether the maximum throttle no-load speed is above 1850. If there is no speed or it is unstable, check the speed sensor and wiring. If the speed is insufficient, adjust the cable or the maximum throttle limit screw and perform throttle calibration. Then adjust to 16-2-OF for the upper structure pressure switch; when operating, it should display 16-2-ON. If there is no change, check the upper structure pressure switch and wiring. Measure the proportional solenoid valve (PS) pressure. Normally, at maximum throttle with no load, the pressure is 3.0 MPa; during operation, the pressure is about 1.6 MPa (related to adjustment). When stalling, the PS pressure will increase as the speed decreases (1800 rpm = 1.6 MPa, 1600 = 1.9 MPa, 1400 = 2.4 MPa, 1200 = 2.8 MPa; inaccurate pressure values for reference only). If the speed and PS pressure changes are normal, perform a PS calibration (L=1.0 MPa, H=3.0 MPa) and throttle calibration. PS pressure calibration method: start the engine, increase throttle to maximum, enter 71, the display shows (71-L-0). 1 is to increase the number, 2 is to decrease, 3 is to move the blinking character right, 4 is to move left. Adjust until the (0) character blinks, then increase the number and the pressure will increase accordingly; decrease the number and the pressure will decrease. Press 8 to save. Normal PS pressure values are (L=0.5 MPa, H=2.5 MPa). Throttle calibration method: enter 70, the display shows (70-P-00). Start the engine, press 8, the speed will rise to high idle, and the display shows (70-P-SP). Press 8 again, the display shows (70--03, to 70--10), and 70--END indicates calibration is complete.
Third, hydraulic pump, model SKP-10. First measure the main pressure. Normal pressure values are: unloading pressure (4 MPa), relief pressure (35 MPa). The working principle of the 320B hydraulic pump is somewhat different from that of the 320. In the 1=1, 2=1 work mode, that is, when a single pump works, the engine also runs at full power (therefore, single-side travel and bucket power are large, which also makes it easier to stall during single bucket relief operations). Its throttle pressure becomes: 1=50%, 2=1. For a single pump, the relief pressure is 35 MPa, and the throttle pressure is 17.5 MPa. For dual pumps, the relief pressure is 35 MPa, and the throttle pressure is nearly 35 MPa. High unloading pressure is also one of the causes of stalling due to clearance. Check whether the power adjustment screw is adjusted too much, and check the plug oil seal inside the adjustment screw. Low throttle pressure is also a main cause of stalling. Low throttle pressure is mainly caused by excessive clearance between the control valve (lifter) servo piston and the pump housing. The standard is no scratches, and the clearance between the lifter and pump housing should be within 0.02 mm, and between the servo piston and pump housing within 0.05 mm.
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