Hydraulic Surge and Control Lag in the Hitachi EX220-3 Excavator

[MikePhua]

The Hitachi EX220 Series and Its Engineering Legacy
The Hitachi EX220-3 excavator belongs to a lineage of mid-sized hydraulic excavators that helped define the brand’s global reputation for reliability and precision. Developed in the late 1990s and early 2000s, the EX220-3 was part of Hitachi’s third-generation series, integrating improved hydraulic control, fuel efficiency, and operator ergonomics. Hitachi Construction Machinery, founded in 1970, had already established itself as a leader in hydraulic systems, and the EX220 series became a staple in infrastructure development, quarrying, and forestry operations.
The EX220-3 is powered by an Isuzu 6BG1T turbocharged diesel engine, delivering approximately 150 horsepower. Its hydraulic system features a variable displacement axial piston pump, load-sensing control, and electronically modulated pilot valves. With an operating weight around 22 metric tons and a bucket breakout force exceeding 14,000 kgf, the machine balances power with finesse.
Terminology Annotation

• Main Hydraulic Pressure: The pressure generated by the primary pump to actuate boom, arm, bucket, and swing functions.
  
• Pilot Control: A low-pressure hydraulic signal system used to modulate the main control valves based on joystick input.
  
• Angle Sensor: An electronic sensor that detects the position of control levers or actuators, used to adjust hydraulic response.
  
• DP Sensor (Differential Pressure Sensor): A sensor that monitors pressure differences across hydraulic components to optimize flow and response.
  

Symptoms of Hydraulic Surge and Control Delay
Operators have reported a peculiar issue with the EX220-3: when gently pulling the boom, arm, or bucket control lever, the engine loads heavily and the main hydraulic pressure spikes from 800 psi to over 4,000 psi before any movement occurs. Once the lever is pulled further, pressure stabilizes and responds proportionally to load and stroke. This behavior is consistent across all engine modes and speeds.
Additionally, when traveling and simultaneously engaging one of these three functions, the tracks surge forward then abruptly slow down—similar to pressing and releasing the accelerator in a car. Notably, swing and travel functions alone operate smoothly, suggesting the issue is isolated to the boom, arm, and bucket circuits.
Diagnostic Path and Sensor Evaluation
Initial diagnostics focused on the angle sensor, which was recalibrated by a technician. However, no improvement was observed. This led to suspicion around the DP sensor, which plays a critical role in modulating pump output based on demand. If the DP sensor fails or sends erratic signals, the pump may overcompensate, causing pressure spikes and engine load before actual movement occurs.
To verify sensor integrity:

• Measure voltage output from the DP sensor during idle and actuation
  
• Compare readings against factory specifications (typically 0.5–4.5V range)
  
• Inspect wiring harness for abrasion, corrosion, or loose connectors
  
• Test pilot pressure at the control valve block to ensure signal consistency
  

If the DP sensor is confirmed faulty, replacement should be followed by a system recalibration using Hitachi’s diagnostic interface or manual pressure tuning.
A Story from the Field
In 2011, a contractor in Alabama experienced this exact issue on a newly acquired EX220-3. After replacing the angle sensor and consulting with a technician who declared the system “normal,” the operator remained unconvinced. Eventually, a retired mechanic suggested inspecting the DP sensor. Upon replacement, the machine’s response normalized, and the erratic pressure surges disappeared. The contractor later noted that this was their first—and last—Hitachi/Deere hybrid, citing the diagnostic complexity compared to older mechanical systems.
Hydraulic System Design and Load-Sensing Behavior
The EX220-3 uses a load-sensing hydraulic system designed to adjust pump output based on actuator demand. Ideally, when a control lever is slightly moved, the pilot signal triggers a proportional response in the main pump. However, if the sensor feedback loop is disrupted, the pump may default to maximum output, causing unnecessary engine load and pressure spikes.
This behavior can be exacerbated by:

• Contaminated hydraulic fluid affecting valve response
  
• Air in the pilot lines causing delayed signal transmission
  
• Sticky spool valves or worn seals in the main control block
  

Routine maintenance should include:

• Hydraulic fluid analysis every 500 hours
  
• Pilot line bleeding after filter replacement
  
• Valve block inspection during annual service intervals
  

Industry Trends and Sensor Reliability
As excavators evolve, electronic sensors increasingly replace mechanical linkages. While this improves precision and fuel efficiency, it also introduces vulnerability to moisture, vibration, and electrical noise. In 2024, Hitachi introduced a new sensor suite with built-in diagnostics and vibration-resistant connectors, reducing false readings and improving uptime.
Aftermarket suppliers now offer upgraded DP sensors with reinforced housings and gold-plated terminals. These components are especially valuable in high-cycle environments such as demolition and quarrying.
Preventative Recommendations and Operator Tips
To maintain optimal hydraulic performance:

• Replace DP and angle sensors every 2,000 hours or during major service
  
• Use OEM-spec hydraulic fluid and filters
  
• Avoid aggressive lever movements during cold starts
  
• Monitor engine load and pressure spikes via onboard diagnostics
  
• Keep spare sensors and pilot line fittings in the service kit
  

Conclusion
The EX220-3’s hydraulic surge and control lag issue is often rooted in sensor miscommunication, particularly involving the DP sensor. While the machine’s core systems are robust, electronic feedback loops must remain intact for smooth operation. By combining sensor diagnostics with fluid maintenance and valve inspection, operators can restore full functionality and extend the life of this iconic excavator. As technology advances, balancing electronic precision with mechanical reliability remains the key to successful earthmoving.