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The Hitachi EX120-2 is a reliable and widely used model in the construction and excavation industries. Known for its durability and efficiency, this hydraulic excavator is designed to handle a range of heavy-duty tasks. However, some operators experience issues where the machine stalls when the control lever is down and the engine is warmed up. Understanding the underlying causes of this issue and finding effective solutions can help operators prevent downtime and ensure smooth operation.
Common Symptoms and Problem Diagnosis
The primary symptom described in these types of problems is the stalling of the engine when the control lever is in the lowered position, and the machine is warmed up. When the machine is in this state, the operator may notice that it becomes increasingly difficult to operate smoothly, or the engine shuts down entirely.
This issue typically becomes apparent after the machine has been running for a while, suggesting that it may be related to temperature or pressure buildup within the system.
Possible Causes of Stalling
Several factors could be causing the stalling issue in the EX120-2. These include:
1. Fuel System Issues
Fuel-related problems are one of the most common reasons for stalling in hydraulic excavators. The EX120-2 uses a fuel system that relies on the timely delivery of fuel to the engine. If there is a fuel delivery problem (e.g., a clogged fuel filter, air in the fuel line, or a failing fuel pump), the engine may lose power and stall, especially under load.
The Hitachi EX120-2 uses hydraulic controls to operate the boom, arm, and other components. If the hydraulic system is malfunctioning, it can cause erratic behavior or stalling.
A malfunction in the electrical system can cause the machine to stall intermittently, particularly when the engine is warmed up. This could be due to faulty wiring, loose connections, or issues with the alternator or battery. Electrical system issues often present as erratic starting behavior or a complete shutdown when the machine is under load.
The engine’s cooling system plays a vital role in maintaining performance and preventing overheating. If the cooling system is not functioning correctly, the engine temperature may rise to unsafe levels, causing the machine to stall.
Sometimes, a mechanical issue with the throttle or control linkage can cause the machine to stall under certain conditions. Over time, the linkage may become worn or misaligned, leading to improper throttle control when the control lever is in the lower position.
To diagnose and resolve the stalling issue in the EX120-2, follow these steps:
1. Inspect the Fuel System
Check the fuel filters for signs of blockage or dirt accumulation. If they appear clogged, replace them. Also, inspect the fuel lines for any signs of leaks or air bubbles. If air is present, bleed the fuel system to remove it.
2. Check the Hydraulic System
Ensure that the hydraulic fluid is at the proper level and free from contaminants. Inspect the hydraulic pump and valves for signs of wear or malfunction. If necessary, replace any worn components and ensure that there is no leakage in the system.
3. Examine the Electrical System
Test the alternator, battery, and wiring for any issues. A failing alternator may need to be replaced, and faulty wiring should be repaired. Also, check for any error codes or diagnostic information from the machine’s onboard ECU (Electronic Control Unit).
4. Monitor Engine Temperature
Check the radiator for any blockages and clean it thoroughly. Ensure that the cooling fan is working correctly and that the engine is not overheating.
5. Inspect the Throttle and Control Linkages
Check the throttle cable and control lever linkage for any signs of damage or misalignment. Adjust or replace these components as necessary to ensure smooth operation.
Conclusion
The Hitachi EX120-2 excavator is a highly reliable machine, but like all complex equipment, it can experience issues such as stalling under specific conditions. By following a systematic diagnostic approach—checking the fuel system, hydraulic components, electrical system, engine temperature, and control linkages—you can identify and address the root cause of the problem. Proper maintenance and regular checks are essential to keep the machine running smoothly and to avoid unexpected breakdowns that can lead to costly repairs and downtime.
Common Symptoms and Problem Diagnosis
The primary symptom described in these types of problems is the stalling of the engine when the control lever is in the lowered position, and the machine is warmed up. When the machine is in this state, the operator may notice that it becomes increasingly difficult to operate smoothly, or the engine shuts down entirely.
This issue typically becomes apparent after the machine has been running for a while, suggesting that it may be related to temperature or pressure buildup within the system.
Possible Causes of Stalling
Several factors could be causing the stalling issue in the EX120-2. These include:
1. Fuel System Issues
Fuel-related problems are one of the most common reasons for stalling in hydraulic excavators. The EX120-2 uses a fuel system that relies on the timely delivery of fuel to the engine. If there is a fuel delivery problem (e.g., a clogged fuel filter, air in the fuel line, or a failing fuel pump), the engine may lose power and stall, especially under load.
- Fuel Filters: Over time, the fuel filters can become clogged with debris, dirt, or even wax buildup from poor-quality fuel. When the filters are blocked, the flow of fuel to the engine is restricted, causing stalling when the engine is under load.
- Air in the Fuel Line: If air is present in the fuel line, it disrupts the proper flow of fuel, leading to engine hesitation or stalling. This issue can be especially prevalent in older machines with worn-out fuel lines or seals.
- Fuel Pump Failure: A faulty fuel pump can also cause stalling, as it may fail to maintain the correct fuel pressure required for proper engine operation.
The Hitachi EX120-2 uses hydraulic controls to operate the boom, arm, and other components. If the hydraulic system is malfunctioning, it can cause erratic behavior or stalling.
- Hydraulic Fluid: Contaminated or low hydraulic fluid levels can lead to improper hydraulic pressure, which may cause the machine to stall when certain control levers are engaged. A hydraulic fluid leak can reduce the fluid levels and affect the system’s operation.
- Hydraulic Pump or Valve Failure: A failing hydraulic pump or valve may struggle to maintain adequate pressure for the system, causing the engine to stall.
- Overheating: Overheating of the hydraulic fluid, due to blocked filters or poor maintenance, could also lead to stalling, particularly in warm conditions.
A malfunction in the electrical system can cause the machine to stall intermittently, particularly when the engine is warmed up. This could be due to faulty wiring, loose connections, or issues with the alternator or battery. Electrical system issues often present as erratic starting behavior or a complete shutdown when the machine is under load.
- Alternator Issues: A malfunctioning alternator may fail to charge the battery correctly, especially when the engine is under load, leading to stalling. If the alternator is not producing sufficient power to the electrical system, the machine may shut down after running for a period.
- Sensors and Control Units: Modern excavators like the EX120-2 rely heavily on electronic sensors and control units to regulate engine operation and hydraulic system functions. A faulty sensor or control unit can send incorrect signals to the engine or hydraulic system, causing the machine to stall.
The engine’s cooling system plays a vital role in maintaining performance and preventing overheating. If the cooling system is not functioning correctly, the engine temperature may rise to unsafe levels, causing the machine to stall.
- Radiator Clogging: A clogged radiator can hinder the cooling system's ability to dissipate heat, leading to engine overheating.
- Cooling Fan Problems: If the cooling fan is malfunctioning or clogged with debris, it will not properly circulate air around the engine, causing it to overheat.
Sometimes, a mechanical issue with the throttle or control linkage can cause the machine to stall under certain conditions. Over time, the linkage may become worn or misaligned, leading to improper throttle control when the control lever is in the lower position.
- Throttle Cable: If the throttle cable is sticking or improperly adjusted, it could lead to stalling when the control lever is used.
- Control Lever Malfunctions: Issues with the control lever mechanism itself, such as a damaged spring or linkage, can prevent the machine from operating smoothly, causing engine stalling.
To diagnose and resolve the stalling issue in the EX120-2, follow these steps:
1. Inspect the Fuel System
Check the fuel filters for signs of blockage or dirt accumulation. If they appear clogged, replace them. Also, inspect the fuel lines for any signs of leaks or air bubbles. If air is present, bleed the fuel system to remove it.
2. Check the Hydraulic System
Ensure that the hydraulic fluid is at the proper level and free from contaminants. Inspect the hydraulic pump and valves for signs of wear or malfunction. If necessary, replace any worn components and ensure that there is no leakage in the system.
3. Examine the Electrical System
Test the alternator, battery, and wiring for any issues. A failing alternator may need to be replaced, and faulty wiring should be repaired. Also, check for any error codes or diagnostic information from the machine’s onboard ECU (Electronic Control Unit).
4. Monitor Engine Temperature
Check the radiator for any blockages and clean it thoroughly. Ensure that the cooling fan is working correctly and that the engine is not overheating.
5. Inspect the Throttle and Control Linkages
Check the throttle cable and control lever linkage for any signs of damage or misalignment. Adjust or replace these components as necessary to ensure smooth operation.
Conclusion
The Hitachi EX120-2 excavator is a highly reliable machine, but like all complex equipment, it can experience issues such as stalling under specific conditions. By following a systematic diagnostic approach—checking the fuel system, hydraulic components, electrical system, engine temperature, and control linkages—you can identify and address the root cause of the problem. Proper maintenance and regular checks are essential to keep the machine running smoothly and to avoid unexpected breakdowns that can lead to costly repairs and downtime.
