Troubleshooting Full Stroke Issues in Hitachi EX120 After Pump Conversion Installation

[MikePhua]

The Hitachi EX120 is a well-regarded hydraulic excavator used in a variety of applications, including construction, mining, and landscaping. Known for its durability and performance, this model is often subjected to modifications or conversions to adapt to different work environments or to extend its lifespan. However, such modifications can occasionally lead to issues, one of which is the hydraulic pump going into full stroke after a conversion installation.
This issue, while not uncommon in hydraulic systems, can be disruptive and lead to operational problems. Understanding why this happens and how to troubleshoot it is essential for any operator or mechanic working on the Hitachi EX120.
Understanding the Full Stroke Issue
In hydraulic systems, the term "full stroke" refers to the maximum range of motion that the hydraulic pump can achieve. When a pump goes into full stroke unexpectedly, it can cause a variety of issues, such as excessive pressure, overheating, or erratic machine behavior. In the case of the Hitachi EX120, this issue is often noticed after modifications to the hydraulic pump, such as a conversion install.
The hydraulic pump in an excavator is responsible for converting mechanical energy from the engine into hydraulic pressure, which drives various components, including the arm, boom, and bucket. A malfunction or modification in the pump can cause the system to behave unpredictably, such as forcing the pump into full stroke mode.
Common Causes of Full Stroke After Pump Conversion

1. Incorrect Pump Installation or Configuration:
   • Symptoms: The hydraulic pump goes into full stroke when the machine is under load, or even when idle.
     
   • Possible Causes:
     • Misalignment of Pump Components: During the conversion or installation, if the pump components (such as the control valve or gear assembly) are not properly aligned, it could cause the pump to go into full stroke unintentionally.
       
     • Incorrect Hydraulic Fluid Flow: Changes made during the conversion could result in improper flow of hydraulic fluid, leading to inconsistent pressures that force the pump into a full stroke.
       
   • Solution: Double-check all components during installation, ensuring that the pump is properly aligned and that the hydraulic fluid flow is calibrated according to the manufacturer's specifications.
     
2. Faulty or Incorrect Pressure Relief Valve:
   • Symptoms: Full stroke of the pump occurs under high load conditions or when the system is under pressure.
     
   • Possible Causes:
     • Over-pressurization: If the pressure relief valve is malfunctioning or incorrectly set, it might not open at the correct pressure, which can cause the pump to attempt a full stroke in an attempt to regulate pressure.
       
   • Solution: Inspect and replace any faulty pressure relief valves. Ensure the valve is properly calibrated to open at the correct pressure for the system.
     
3. Control Valve or Pilot Circuit Issues:
   • Symptoms: Sudden changes in speed or movement, or the system struggles to stabilize after modifications.
     
   • Possible Causes:
     • Malfunctioning Control Valves: The control valve, which regulates fluid flow to the hydraulic pump, may be incorrectly calibrated or damaged after the conversion. A malfunction here can cause the pump to go into full stroke mode due to improper fluid routing.
       
     • Pilot Circuit Problems: The pilot circuit, which controls smaller valves within the hydraulic system, might also be affected during the modification, causing improper signals to reach the main pump and resulting in full stroke operation.
       
   • Solution: Check the control valves and pilot circuits to ensure they are operating correctly. If any part is damaged or miscalibrated, replace or repair it.
     
4. Improper Hydraulic Fluid or Contaminants:
   • Symptoms: Full stroke behavior is observed sporadically, or the system overheats.
     
   • Possible Causes:
     • Dirty or Incorrect Fluid: If the hydraulic fluid is contaminated with dirt, debris, or improper additives, it can cause the system to behave erratically, leading to issues like full stroke.
       
     • Low Fluid Levels: Low hydraulic fluid levels after conversion can result in air pockets or incorrect flow, causing the pump to go into full stroke to compensate.
       
   • Solution: Replace the hydraulic fluid with the correct type recommended by the manufacturer. Perform a fluid flush and replace any clogged filters. Ensure that fluid levels are checked regularly.
     
5. Improper Electrical Wiring or Sensor Failures:
   • Symptoms: Unpredictable pump behavior, such as random full stroke occurrences.
     
   • Possible Causes:
     • Electrical Interference: If there were modifications to the electrical system during the pump conversion, it could cause intermittent issues in the sensors or control systems, leading to unexpected pump behavior.
       
     • Faulty Sensors: Sensors that monitor fluid pressure or flow may be damaged or incorrectly calibrated, leading the control system to mistakenly signal for full stroke.
       
   • Solution: Inspect the wiring and electrical connections for any signs of wear or damage. Test the sensors that monitor hydraulic system pressure and flow, and replace any faulty components.
     

Troubleshooting Steps for the Full Stroke Problem
To address the full stroke issue after a pump conversion, follow this systematic troubleshooting approach:

1. Step 1: Inspect the Pump Installation:
   • Ensure that the pump is installed correctly and aligned with the rest of the hydraulic system.
     
   • Verify that all components were properly tightened and that no parts were overlooked during the conversion.
     
2. Step 2: Check the Pressure Relief Valve:
   • Inspect the pressure relief valve to ensure it is set to the correct pressure and is functioning properly.
     
   • If the valve is stuck or set too high, it can cause the pump to run in full stroke mode. Adjust or replace the valve as needed.
     
3. Step 3: Examine the Control Valves and Pilot Circuits:
   • Check the control valves for leaks, blockages, or misalignments that may be causing fluid flow issues.
     
   • Test the pilot circuit for any abnormalities and make sure that the system is receiving accurate pressure and flow signals.
     
4. Step 4: Evaluate the Hydraulic Fluid:
   • Replace the hydraulic fluid and filters, ensuring that no contaminants are present in the system.
     
   • Check the fluid levels and ensure they are at the appropriate level for optimal system function.
     
5. Step 5: Inspect the Electrical System and Sensors:
   • Check all wiring for potential damage or faulty connections that may interfere with sensor readings or control signals.
     
   • Test the sensors and replace any that are malfunctioning or out of calibration.
     

Real-World Example: Resolving Full Stroke Issue in a Hitachi EX120
A mechanic working on a Hitachi EX120 after a pump conversion encountered the full stroke issue. The pump would unexpectedly go into full stroke, causing overheating and erratic behavior during operation. Upon inspection, it was found that the pressure relief valve had not been calibrated correctly during the conversion, leading to over-pressurization.
After adjusting the pressure relief valve and ensuring that the hydraulic fluid was clean and at the proper level, the issue was resolved. The operator reported that the machine returned to normal performance, and no further full stroke incidents occurred.
Conclusion
The full stroke issue in the Hitachi EX120 after a pump conversion is a common hydraulic problem that can be caused by several factors, including incorrect installation, faulty valves, or issues with the hydraulic fluid or sensors. By following a structured troubleshooting process and addressing potential causes such as pressure relief valve misalignment, control valve malfunctions, or fluid contamination, the issue can be effectively resolved.
Operators and mechanics working on the EX120 should pay close attention during conversions or modifications to ensure that all components are properly calibrated and that the system is operating optimally. Regular maintenance and timely troubleshooting are key to maintaining the performance and longevity of the hydraulic system in these machines.