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August 13, 2020
[Maintenance knowledge] What are the reasons why the excavator cannot start
Don’t panic when the excavator is unable to start while working outside. The starting circuit may malfunction and the engine may not start normally.
The starting circuit of the excavator is mainly composed of
The starter works abnormally. This type of fault is manifested as when the engine starts, the starter relay can be normally closed. But the starter does not work or does not work normally. The troubleshooting methods are as follows:
1. Check the excavator battery. The battery voltage must be higher than 24V to start the engine. If the battery voltage is insufficient, charge it. If it is still lower than 24V after charging, replace it with a new battery.
2. Check the power switch of the excavator. If the contacts of the main power switch are not in good contact, the voltage drop before and after the contacts will increase, resulting in a decrease in the voltage of the excavator or no electricity. At this time, it is enough to grind the contacts or replace the main power switch.
3. Check the battery relay of the excavator. If the contact of the battery relay is in poor contact when it is closed, the starting voltage may be low and the starter will not work or work normally. At this time, repair or replace the battery relay. The fourth is to check the starting relay. When the starter relay is closed, if the contacts are not in poor contact, the starter terminal voltage may be low, resulting in the starter not working or the speed is too low. At this time, repair or replace the starting relay. The fifth is to check the starter. When the engine is started, the performance of the starter can be judged by measuring the voltage value between the two terminals of the starter. Both the B terminal voltage and C terminal voltage of the starter should be higher than 23V, and the grounding wire should be well grounded. If the voltage of B terminal and C terminal is lower than 23V, the starter should be repaired or replaced. (2) The starting relay works abnormally. This type of fault is manifested as the starting relay does not pick up or picks up badly when the engine starts. The troubleshooting methods are as follows: First, check insurance. Start-up insurance is generally located in a multi-channel fuse box, and its rated current is 7.5A. If the fuse is improperly installed or the wiring harness is damaged and grounded, it may cause the fuse to blow. At this time, check whether the insurance is installed correctly and whether the insurance is intact. If the insurance is damaged, replace it. The second is to check the start relay. If the starting relay does not pull in or pulls in badly, it means that the performance of the starting relay coil is poor. At this time, it can be judged by measuring the power supply voltage of the starting relay. If the voltage is lower than 23V, the starting relay should be replaced. The third is to check the starting protection relay. Before starting the engine, the starting protection relay contact should be in a conducting state. At this time, you can measure whether both ends of the start protection relay contact are conductive. If it is not conductive or the resistance is greater than 1Ω, the start protection relay should be replaced.
4. Check the main controller circuit board of the excavator. When checking, first turn on the ignition switch, and then measure the voltage of the coil control terminal of the start protection relay (the voltage should be about 24V). If there is no voltage at the control terminal, you can remove the wire and test the machine. If the engine starts normally after removing the wire, it may be a problem with the wiring harness and just replace the wiring harness; if the wiring harness is normal, the main controller circuit board should be replaced.
5. Check the excavator satellite positioning system (GPS). When checking, first turn on the ignition switch, and then connect the multimeter between the 22-1.25Y and 21-1.25LY wires connected to the GPS. If the resistance of these two wires is greater than 1Ω, check whether the connectors connected to the GPS are in poor contact, or there is a problem with the GPS setting. If the wire is in poor contact with the connector, or there is a problem with the GPS setting, replace the GPS connection connector or adjust the GPS setting.
6. Check the ignition switch of the excavator. When the ignition switch is turned on (except for the starter, other circuits are turned on), the voltage value of the B terminal should be higher than 23V. When the ignition switch is set to the "Start" position, there should be conduction between its B and C terminals. If the voltage value of the ignition switch B terminal is less than 23V, replace the ignition switch. (3) The engine stalls after the engine is started. This type of fault is manifested as when the engine is started, the starter and the starter relay are working normally, but the engine cannot be started or the engine stalls quickly after starting. The troubleshooting methods of this type of fault are as follows: First, check the oil cut valve relay. Turn the ignition switch to the "Start" position and measure the voltage between the control terminal of the fuel cut-off valve relay and the ground terminal. If its voltage is higher than 23V, and the oil cut-off valve relay still cannot be closed normally, or the voltage difference between the front and back of the contact is greater than 1V after being closed, the oil cut-off valve relay should be replaced. The second is to check the power supply of the oil cutoff valve. If the power supply of the fuel cutoff valve is cut off, the engine will quickly go out after the engine starts. At this time, you can turn the ignition switch to the "ON" position, and measure the voltage of the fuel cutoff valve to be no less than 24V. If it is lower than 24V, check the circuit from the oil cutoff valve to the oil cutoff valve relay. The third is to check the related wiring harness and grounding. According to the composition of the fuel supply control circuit and the specific faults, the related wiring harness can be checked. If the connecting harness is damaged, it should be replaced. The fourth is to check the oil shutoff valve. After the engine is started, observe whether the shutoff valve is operating normally. If the fuel cut-off valve has no pull-in action, first check whether the ignition switch power supply is about 24V, and then check whether the fuel cut-off valve pull-in power cord is about 24V when the engine is started, and whether the grounding wire is well grounded. If the above power cord and grounding wire are normal, it can be judged that the oil cutoff valve is faulty, just replace the oil cutoff valve.