10-23-2025, 01:27 AM
A Hitachi EX100-2 excavator experiencing jerky bucket curl-out and engine stalling during hydraulic functions likely suffers from pump control failure, electrical lockout, or limp mode activation. Systematic inspection of the PVC controller, fuses, and pump stop rod orientation is essential to restore normal operation.
Hitachi EX100-2 Overview
The EX100-2 is a mid-size hydraulic excavator introduced by Hitachi in the early 1990s, designed for general excavation, trenching, and light demolition. It features a 4-cylinder Isuzu diesel engine, dual hydraulic pumps, and an electronically modulated control system. Hitachi Construction Machinery, founded in 1970, has delivered thousands of EX-series machines globally, with the EX100-2 widely used in North America and Asia for its reliability and ease of service.
The EX100-2 uses a PVC (Pump Valve Controller) to regulate hydraulic output based on operator input and engine load. When the PVC fails or enters limp mode, the pump stroke is mechanically limited, reducing flow and disabling full hydraulic function.
Terminology Notes
The machine tracked and operated normally except for the bucket curl-out, which became jerky and caused engine stalling. Later, all hydraulic functions began stalling the engine, suggesting the pumps were stuck at full stroke. The PVC controller behind the seat showed no flashing light, indicating a possible electrical fault.
Steps taken:
In limp mode, the stop rod faces away from the engine, physically limiting piston stroke. This reduces hydraulic flow and allows the machine to operate with minimal load. To engage limp mode manually:
Field Anecdotes and Practical Insight
In Ontario, a technician restored limp mode on a Deere 490E (similar pump design) by removing the solenoids and manually lifting the piston. He used a wooden dowel and gentle pressure to avoid scoring the pump housing.
In Alabama, an operator discovered that a fried PVC resistor had disabled all hydraulic modulation. He bypassed the controller and used limp mode to drive the machine back to the shop for full repair.
Recommendations for Repair and Recovery
Hydraulic failure on the Hitachi EX100-2 often stems from electrical faults in the PVC or mechanical issues in the pump control system. Understanding limp mode mechanics and stop rod orientation allows operators to recover functionality and transport the machine safely. With careful inspection and methodical troubleshooting, even complex failures can be resolved in the field.
Hitachi EX100-2 Overview
The EX100-2 is a mid-size hydraulic excavator introduced by Hitachi in the early 1990s, designed for general excavation, trenching, and light demolition. It features a 4-cylinder Isuzu diesel engine, dual hydraulic pumps, and an electronically modulated control system. Hitachi Construction Machinery, founded in 1970, has delivered thousands of EX-series machines globally, with the EX100-2 widely used in North America and Asia for its reliability and ease of service.
The EX100-2 uses a PVC (Pump Valve Controller) to regulate hydraulic output based on operator input and engine load. When the PVC fails or enters limp mode, the pump stroke is mechanically limited, reducing flow and disabling full hydraulic function.
Terminology Notes
- PVC (Pump Valve Controller): An electronic module that controls pump displacement and hydraulic response.
- Stop Rod and Plate: A mechanical limiter inside the pump that restricts piston stroke when rotated into limp mode.
- Limp Mode: A fail-safe condition that limits hydraulic output to prevent damage when the control system fails.
- Solenoids: Electrically actuated valves that modulate hydraulic flow based on PVC signals.
The machine tracked and operated normally except for the bucket curl-out, which became jerky and caused engine stalling. Later, all hydraulic functions began stalling the engine, suggesting the pumps were stuck at full stroke. The PVC controller behind the seat showed no flashing light, indicating a possible electrical fault.
Steps taken:
- Checked all fuses, found an oversized fuse in slot F7, possibly damaging the PVC.
- Inspected the PVC resistor under the top cover for burn marks.
- Noted the pump stop rod was facing the engine, indicating normal mode.
- Attempted to rotate the stop plate 180 degrees to engage limp mode manually.
In limp mode, the stop rod faces away from the engine, physically limiting piston stroke. This reduces hydraulic flow and allows the machine to operate with minimal load. To engage limp mode manually:
- Remove the stop plate and rotate it 180 degrees.
- Reinstall the plate so the rod contacts the piston base.
- Push the piston upward while securing the plate.
Field Anecdotes and Practical Insight
In Ontario, a technician restored limp mode on a Deere 490E (similar pump design) by removing the solenoids and manually lifting the piston. He used a wooden dowel and gentle pressure to avoid scoring the pump housing.
In Alabama, an operator discovered that a fried PVC resistor had disabled all hydraulic modulation. He bypassed the controller and used limp mode to drive the machine back to the shop for full repair.
Recommendations for Repair and Recovery
- Inspect PVC Resistor and Fuses: Replace damaged components and use correct fuse ratings.
- Use Limp Mode for Emergency Travel: Rotate stop plate and relieve control oil to limit pump stroke.
- Check Solenoids and Wiring: Faulty solenoids can mimic PVC failure.
- Document Stop Rod Position: Normal mode faces engine; limp mode faces outward.
- Avoid Forcing Components: Use controlled pressure and avoid hammering or prying.
Hydraulic failure on the Hitachi EX100-2 often stems from electrical faults in the PVC or mechanical issues in the pump control system. Understanding limp mode mechanics and stop rod orientation allows operators to recover functionality and transport the machine safely. With careful inspection and methodical troubleshooting, even complex failures can be resolved in the field.
