Troubleshooting the EX-200 with Conversion Kit: Stalling When Boom Is Lowered

[MikePhua]

The Hitachi EX-200, a popular model in the EX series of hydraulic excavators, is known for its versatility, durability, and powerful hydraulics. However, like any heavy equipment, it can encounter operational challenges, particularly when modifications are made to its systems. One such issue is when the EX-200 stalls after the boom is lowered, which can be perplexing for operators.
This issue is especially relevant for machines that have undergone a conversion kit installation. Conversion kits, often used to upgrade or modify the machine's capabilities, can sometimes introduce complications that weren’t present in the original configuration. Understanding the root causes of stalling when lowering the boom can help resolve this problem effectively.
Overview of the Hitachi EX-200 and Its Capabilities
The Hitachi EX-200 is a mid-sized excavator that is commonly used in construction, demolition, and mining tasks. With a 120-horsepower engine and advanced hydraulics, the EX-200 is known for its efficient digging, lifting, and material-handling capabilities. However, when modifications such as a conversion kit are installed to alter its configuration, these changes can occasionally introduce issues that affect its overall performance.
Conversion kits are typically used to enhance certain features of a machine, such as improving fuel efficiency, increasing hydraulic power, or making the equipment more adaptable to different attachments. However, these modifications must be installed correctly to avoid unexpected mechanical problems.
Common Causes of Stalling in Modified EX-200 Machines
When the EX-200 stalls after the boom is lowered, it can typically be traced to specific causes within the hydraulic or fuel systems. Since the issue arises when the boom is lowered, it suggests a hydraulic problem, which could be linked to the machine's load management, pressure regulation, or system compatibility with the newly installed conversion kit. Here are some common causes of stalling:
1. Hydraulic Pressure Imbalance

• What Happens: The hydraulic system in the EX-200 works by creating and maintaining pressure to perform various tasks, including lifting, digging, and moving the boom. When lowering the boom, the hydraulic system should be able to release pressure gradually. If the pressure is not managed correctly, it can cause the engine to stall.
  
• Possible Causes:
  • Improper Pressure Relief Settings: After installing a conversion kit, the pressure relief valves might not be properly adjusted to account for the changes in the hydraulic system. This imbalance can lead to excessive pressure, which causes the engine to stall when the boom is lowered.
    
  • Hydraulic Fluid Contamination: Contaminated hydraulic fluid can cause the system to operate inefficiently, resulting in excess pressure build-up. This can affect the operation of the boom and lead to stalling.
    

2. Incompatibility with Conversion Kit

• What Happens: Conversion kits often alter certain specifications of the machine, such as the hydraulic flow rate or pressure settings, to adapt the excavator for new functions or attachments. However, these kits are sometimes not fully compatible with the original system, leading to stalling issues.
  
• Possible Causes:
  • Incorrect Kit Installation: If the conversion kit was not installed correctly or was not intended for the EX-200 model, it could cause performance issues, such as excessive hydraulic pressure or poor system calibration.
    
  • Flow Control Problems: The flow rate in the hydraulic system is critical for smooth operation. If the conversion kit alters the flow rate or hydraulic capacity without proper adjustments, the machine may stall when the boom is lowered due to insufficient hydraulic support.
    

3. Fuel System Problems

• What Happens: Fuel system issues, such as air in the lines, improper fuel flow, or low fuel pressure, can also cause the engine to stall, especially under load conditions like lowering the boom.
  
• Possible Causes:
  • Air in Fuel Lines: After a modification or during routine maintenance, air can enter the fuel lines, leading to inconsistent fuel delivery to the engine. This could cause the engine to stall under higher load conditions, such as when lowering the boom.
    
  • Fuel Pump Malfunction: If the fuel pump is not supplying enough fuel to the engine, the system will not operate at optimal capacity, causing the engine to stall when the hydraulic demand increases.
    

4. Excessive Load on the Boom or Hydraulic System

• What Happens: If the EX-200 is tasked with lifting or moving too much weight, the hydraulic system may become overwhelmed. This puts a strain on the entire system and may lead to stalling when the boom is lowered.
  
• Possible Causes:
  • Overloaded Boom: When the boom is overloaded, the hydraulic system has to work harder to manage the load. This additional strain can cause the system to stall.
    
  • Incorrect Load Distribution: If the load is unevenly distributed or improperly balanced, the hydraulic system might struggle to handle the extra pressure, leading to stalling.
    

Step-by-Step Troubleshooting Guide
To resolve the stalling issue in the EX-200 when lowering the boom, follow this step-by-step troubleshooting guide:
1. Check Hydraulic Pressure Settings

• What to Do: Inspect the pressure relief valves and ensure they are properly adjusted for the system after the conversion kit installation. The pressure settings should be matched to the new specifications of the kit.
  
• Why It Matters: If the pressure relief settings are too high or too low, they can cause the hydraulic system to become unstable, leading to stalling.
  

2. Inspect Hydraulic Fluid Quality and Levels

• What to Do: Check the hydraulic fluid for any signs of contamination or degradation. If the fluid is dirty, drain and replace it with fresh fluid to prevent clogging and ensure smooth operation.
  
• Why It Matters: Contaminated fluid can reduce the efficiency of the hydraulic system and cause blockages or pressure inconsistencies, which lead to engine stalling.
  

3. Verify Conversion Kit Compatibility

• What to Do: Ensure the conversion kit is fully compatible with the EX-200 model. Check the installation manual to confirm that all components, such as pressure regulators and flow control devices, are correctly installed and calibrated.
  
• Why It Matters: Incompatibility between the kit and the original system can create pressure imbalances, flow restrictions, and other issues that lead to stalling.
  

4. Examine the Fuel System

• What to Do: Inspect the fuel system for air in the lines or fuel pump issues. Ensure there are no blockages and that fuel is flowing smoothly to the engine.
  
• Why It Matters: Air in the fuel lines or an improperly functioning fuel pump can cause the engine to stall, particularly when under load.
  

5. Check Load and Boom Operations

• What to Do: Assess the load being lifted by the EX-200 and ensure it is within the machine's rated capacity. If the boom is overloaded, reduce the weight or redistribute it more evenly.
  
• Why It Matters: Overloading the boom puts unnecessary strain on the hydraulic system, leading to stalling issues when the boom is lowered.
  

Preventive Maintenance Tips

• Regularly Monitor Hydraulic Pressure: Regularly inspect and adjust the hydraulic pressure settings, especially after any modifications or upgrades.
  
• Use High-Quality Hydraulic Fluid: Always use the recommended hydraulic fluid and change it at regular intervals to prevent contamination.
  
• Check for System Leaks: Ensure all hydraulic hoses and connections are tight and free of leaks to prevent pressure loss.
  
• Ensure Proper Load Handling: Always ensure the load is within the rated capacity of the machine, and avoid sudden, jerky movements with the boom.
  

Conclusion
The stalling issue in the Hitachi EX-200, particularly after a conversion kit is installed, is often related to problems in the hydraulic or fuel systems. Ensuring that the hydraulic pressure is properly balanced, the fuel system is free of air, and the conversion kit is compatible with the original system will help resolve the problem. Regular maintenance, combined with proper troubleshooting, can prevent further stalling issues and keep the EX-200 operating efficiently.