Resolving Hydraulic Lag and Engine Stalling in the Hitachi EX100-2

[MikePhua]

The EX100-2 and Its Electronic-Hydraulic Integration
The Hitachi EX100-2 excavator, part of the Dash-2 series introduced in the early 1990s, represented a significant leap in integrating electronic control with hydraulic precision. Designed for mid-size earthmoving and utility work, the EX100-2 featured a load-sensing hydraulic system, electronic controllers (EC and PVC), and a variable displacement pump regulated by proportional solenoids. With an operating weight around 10 metric tons and a dig depth exceeding 6 meters, it became a staple in Southeast Asia and other developing markets due to its balance of power and serviceability.
However, as these machines age past 8,000 hours, symptoms such as sluggish controls, stalling under load, and erratic hydraulic response begin to surface. These issues often stem from a combination of electronic miscommunication, fuel delivery inconsistencies, and mechanical wear in the pump regulator system.
Terminology and Component Notes
- PVC (Pump Valve Controller): An electronic module that regulates hydraulic pump output based on operator input and sensor feedback.
- EC (Engine Controller): Manages engine speed and communicates with the PVC to balance power demand.
- PDSV (Proportional Directional Solenoid Valve): Controls hydraulic flow direction and volume based on electrical signals.
- Angle Sensor Fork: A mechanical linkage that translates pump swashplate position into electrical feedback for the PVC.
- Banjo Bolt Screen: A fine mesh filter embedded in fuel line fittings, often overlooked during routine maintenance.
Symptoms and Initial Troubleshooting
One operator reported that the EX100-2 ran normally until suddenly all hydraulic functions became slow, and the engine bogged down or stalled when cylinders were fully extended. Despite replacing the EC, PVC, PDSV valves, and checking fuses, the issue persisted. The machine lacked a DR ZX diagnostic tool, making fault code retrieval difficult.
Initial steps taken included:

• Cleaning fuel lines and replacing return hoses
  
• Swapping electronic controllers from a donor machine
  
• Verifying fuse integrity and harness continuity
  
• Attempting to read fault codes via PVC status light
  

These efforts ruled out basic electrical faults and pointed toward deeper hydraulic or sensor-related issues.
Hydraulic Pump Regulation and Spool Behavior
The EX100-2 uses a variable displacement axial piston pump with an electronically modulated regulator. If the regulator spool sticks due to contamination or wear, the pump may fail to adjust displacement properly, leading to low flow and engine overload during high-demand operations.
Recommended inspection steps:

• Remove and clean the pump regulator spool and housing
  
• Check for varnish buildup or scoring on spool surfaces
  
• Verify free movement of the angle sensor fork and linkage
  
• Lubricate pivot points and confirm sensor feedback voltage
  
• Replace O-rings and seals to prevent internal leakage
  

One technician noted that a similar issue was resolved by freeing a stuck spool and recalibrating the PVC using manual voltage input, restoring full hydraulic response.
Fuel System Integrity and Hidden Restrictions
White smoke, stalling, and sluggish performance can also result from restricted fuel flow. While filters are often replaced, the banjo bolt screen—located inside the fuel inlet fitting—is frequently overlooked. A partially clogged screen can starve the injection pump, especially under load.
Fuel system checklist:

• Remove and inspect banjo bolt screens for debris
  
• Replace all rubber fuel lines with diesel-rated hose
  
• Bleed the system thoroughly after component replacement
  
• Test lift pump output and injection timing
  
• Monitor fuel return flow for signs of injector leakage
  

In one case, cleaning the banjo bolt screen restored engine power and eliminated stalling, despite no visible contamination in the main filter.
Reading Fault Codes Without Diagnostic Tools
The EX100-2’s PVC module includes a status light that can flash fault codes. While the DR ZX tool is ideal, codes can sometimes be interpreted manually by counting flashes and referencing service documentation. Unfortunately, many operators lack access to the EX100 manual and rely on EX200-2 documentation as a substitute.
Manual code retrieval tips:

• Turn ignition on and observe PVC status light
  
• Count long and short flashes to determine code sequence
  
• Cross-reference with known fault tables from similar models
  
• Document code behavior during different operating conditions
  

Operators have shared that even without a DR ZX, basic fault identification is possible with patience and a flashlight.
Hitachi’s Dash-2 Series Legacy and Market Impact
Hitachi’s Dash-2 series, including the EX100-2, EX200-2, and EX300-2, marked a shift toward electronically enhanced excavators. These machines offered better fuel efficiency, smoother hydraulics, and improved diagnostics compared to purely mechanical predecessors. Their success in Asia, Africa, and Latin America was driven by parts availability and robust design.
Sales of the EX100-2 were strong throughout the 1990s, with many units still in operation. Hitachi’s modular controller design allowed for field swaps and simplified troubleshooting, though aging electronics now pose challenges for unsupported fleets.
Conclusion
Sluggish hydraulics and stalling in the Hitachi EX100-2 are often the result of pump regulator spool issues, fuel delivery restrictions, or sensor miscommunication. By combining mechanical inspection with targeted electrical testing, operators can restore performance without relying solely on diagnostic tools. In the world of aging excavators, insight and persistence often outperform software—and every smooth boom movement is a testament to hands-on problem solving.