Hitachi EX120 Engine Stalling Under Load: Causes and Solutions

[MikePhua]

The Hitachi EX120 is a reliable hydraulic excavator known for its durability and versatility in various construction and digging tasks. However, like any piece of heavy machinery, the EX120 can face operational challenges, one of the most common being engine stalling under load. This issue can occur for a variety of reasons, ranging from fuel system problems to electrical issues, and can lead to significant downtime if not diagnosed and fixed promptly.
This article will explore the potential causes of engine stalling under load in the Hitachi EX120, common symptoms, diagnostic steps, and possible solutions to resolve the issue.
Understanding the Hitachi EX120
The Hitachi EX120 is part of the EX series of hydraulic excavators, which are known for their efficient fuel consumption, powerful hydraulic systems, and exceptional digging capabilities. The machine is powered by a diesel engine that provides the necessary torque and horsepower to operate heavy equipment effectively. The EX120 is used in a variety of applications, including construction, demolition, and mining.
The engine stalling issue is one of the problems that operators may encounter with this machine. Stalling under load refers to the engine shutting off or losing power when the excavator is required to exert more force or work under demanding conditions, such as digging into hard soil or lifting heavy materials.
Potential Causes of Engine Stalling Under Load
Several factors can contribute to engine stalling in the Hitachi EX120 when the machine is under load. These factors can involve the fuel system, air intake system, electrical components, and engine management system. Let’s break down these potential causes.
1. Fuel Delivery Issues
A common reason for engine stalling under load is inadequate fuel delivery. If the engine isn't receiving enough fuel, it can stall when the machine is under load, as more power is required.
Possible Causes:

• Clogged fuel filters: Over time, fuel filters can become clogged with dirt and debris, restricting the flow of fuel to the engine.
  
• Faulty fuel injectors: Worn or malfunctioning fuel injectors can lead to poor fuel atomization, causing inconsistent combustion and stalling.
  
• Fuel pump issues: If the fuel pump is not working correctly, it may fail to supply enough fuel under load.
  

Symptoms:

• Engine stalling after working for a while under load.
  
• Difficulty starting the engine after stalling.
  

Solution:

• Inspect and replace the fuel filters if they are clogged or dirty.
  
• Check the fuel injectors for proper functioning and clean or replace them if necessary.
  
• Test the fuel pump and replace it if it is malfunctioning.
  

2. Air Intake Problems
The air intake system is crucial for the engine's combustion process. If there is a blockage or restriction in the air intake, it can cause the engine to stall under load due to a lack of air.
Possible Causes:

• Clogged air filters: If the air filters are clogged, the engine may not be receiving enough air for proper combustion.
  
• Air intake leaks: Any cracks or leaks in the intake manifold or hoses can lead to an air-fuel mixture imbalance, causing the engine to stall.
  

Symptoms:

• Decreased engine performance, especially under load.
  
• Increased fuel consumption.
  

Solution:

• Inspect and replace air filters if they are dirty or clogged.
  
• Check the air intake system for leaks or cracks and repair any found.
  

3. Fuel Contamination or Quality Issues
Contaminated or poor-quality fuel can cause the engine to stall under load by affecting the combustion process.
Possible Causes:

• Water in the fuel: Water can enter the fuel tank due to condensation or during refueling, causing the engine to misfire or stall.
  
• Contaminants in the fuel: Dirt, rust, or other debris in the fuel can clog the fuel lines and injectors, affecting performance.
  

Symptoms:

• Sudden stalling or misfiring under load.
  
• Rough engine operation.
  

Solution:

• Drain and replace the contaminated fuel with fresh, high-quality diesel fuel.
  
• Inspect and clean the fuel tank to remove any contaminants or water.
  

4. Electrical or Sensor Malfunctions
The engine control unit (ECU) and various sensors in the Hitachi EX120 work together to regulate engine performance. A malfunction in these components can lead to stalling under load.
Possible Causes:

• Faulty sensors: Malfunctioning sensors, such as the mass airflow sensor (MAF) or crankshaft position sensor, can cause the engine to stall when they fail to send accurate data to the ECU.
  
• Electrical issues: Loose connections or damaged wiring in the electrical system can interfere with engine control, causing stalling.
  

Symptoms:

• Intermittent stalling, especially under load.
  
• Engine running rough or in "limp mode."
  

Solution:

• Check the electrical wiring and connectors for signs of damage, corrosion, or loose connections.
  
• Inspect and replace any faulty sensors to ensure proper engine control.
  

5. Engine Overheating
An overheating engine can cause it to stall when under load. When the engine temperature rises above normal operating levels, it can trigger a safety feature to prevent further damage.
Possible Causes:

• Low coolant levels: Insufficient coolant can lead to overheating.
  
• Faulty thermostat or cooling fan: If the thermostat is stuck or the cooling fan is not working, the engine can overheat quickly.
  

Symptoms:

• The engine temperature gauge reading higher than usual.
  
• The engine stalling after running for a while.
  

Solution:

• Check the coolant levels and top them up if necessary.
  
• Inspect the thermostat and cooling fan for proper operation and replace them if faulty.
  

Steps for Diagnosing and Fixing Engine Stalling Under Load
To troubleshoot engine stalling in the Hitachi EX120, follow these steps:

1. Check Fuel System: Inspect the fuel filters for clogging and replace them. Test the fuel pump for adequate pressure and clean or replace the fuel injectors.
   
2. Inspect Air Intake: Check the air filters for blockages and replace them if necessary. Look for any leaks or cracks in the air intake system.
   
3. Test Fuel Quality: Drain any contaminated fuel and replace it with fresh fuel. Clean the fuel tank if necessary.
   
4. Examine the Electrical System: Inspect the wiring and connectors for damage. Test and replace any malfunctioning sensors, such as the mass airflow sensor or crankshaft position sensor.
   
5. Monitor Engine Temperature: Keep an eye on the engine temperature gauge. If the engine is overheating, inspect the coolant levels and the cooling system components.
   

Conclusion
Engine stalling under load in the Hitachi EX120 is a frustrating issue that can hinder productivity and lead to unnecessary downtime. By identifying the root causes of the problem, such as fuel delivery issues, air intake blockages, or electrical malfunctions, operators can address the issue efficiently and restore the excavator to full working condition.
Regular maintenance and timely diagnostics can prevent most stalling issues and ensure that the EX120 remains a reliable and powerful machine in demanding work environments. If the stalling persists after performing basic troubleshooting, it may be best to consult a qualified technician or Hitachi service center for further assistance.