Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Throttle Control Issues in Komatsu PC78MR-6 Excavators
#1
The Komatsu PC78MR-6 is a compact midi-excavator renowned for its versatility and performance in confined spaces. However, some operators have reported issues with the throttle system, particularly concerning the engine's inability to rev up properly. Understanding the potential causes and solutions is essential for maintaining optimal machine performance.
Common Causes of Throttle Problems
  1. Auto-Idle Switch Activation
    The PC78MR-6 is equipped with an auto-idle feature to reduce fuel consumption during periods of inactivity. If the auto-idle button on the joystick is engaged, the engine speed may be limited, preventing full throttle operation. Ensure that the auto-idle button is disengaged to allow the engine to reach full RPM.
  2. Faulty Throttle Motor Assembly
    The throttle motor assembly, identified by part numbers 21W-43-41321 and 21W-43-41322, controls the engine's throttle valve. A malfunction in this component can lead to erratic or insufficient throttle response. Replacement units are available from various suppliers, with prices typically ranging from $250 to $300.
  3. Electrical or Sensor Faults
    Error codes such as E02, E03, and E41 may indicate issues with the throttle control system. These codes often point to problems with sensors or electrical connections affecting throttle performance. Inspecting and repairing these components can resolve related issues.
Troubleshooting Steps
  • Check Auto-Idle Setting: Verify that the auto-idle button on the joystick is not engaged.
  • Inspect Throttle Motor: Listen for unusual noises from the throttle motor and check for any visible signs of wear or damage.
  • Examine Electrical Connections: Ensure all wiring and connectors related to the throttle system are secure and free from corrosion.
  • Consult Diagnostic Codes: Use the machine's diagnostic system to retrieve any error codes that may provide insight into the issue.
Preventive Maintenance Tips
  • Regularly Test Throttle Response: Periodically check the throttle's responsiveness to ensure it operates smoothly.
  • Keep Electrical Components Clean: Regularly clean connectors and terminals to prevent corrosion and ensure proper electrical contact.
  • Monitor for Error Codes: Use the diagnostic system to monitor for any emerging error codes that could indicate developing issues.
Conclusion
Throttle control issues in the Komatsu PC78MR-6 can stem from various sources, including user settings, component malfunctions, and electrical faults. By systematically troubleshooting and addressing these potential causes, operators can maintain the excavator's performance and longevity. Regular maintenance and prompt attention to emerging issues are key to ensuring the machine operates at its best.
Reply


Messages In This Thread
Throttle Control Issues in Komatsu PC78MR-6 Excavators - by MikePhua - 08-24-2025, 02:21 PM

Possibly Related Threads…
Thread Author Replies Views Last Post
  Identifying and repairing shifting issues on a vintage Hough loader MikePhua 0 10 9 hours ago
Last Post: MikePhua
  Troubleshooting the JCB 532 Loadall: Common Issues and Solutions MikePhua 0 10 9 hours ago
Last Post: MikePhua
  Troubleshooting Travel Issues on a Case 340 Skid Steer MikePhua 0 10 9 hours ago
Last Post: MikePhua
  Case 580B Throttle Foot Feed Return Spring Maintenance MikePhua 0 7 9 hours ago
Last Post: MikePhua
  Case W36 Hydraulic Issues and Troubleshooting MikePhua 0 10 10 hours ago
Last Post: MikePhua
  Diagnosing Control Lag in the Simon 32' All-Terrain Scissor Lift MikePhua 0 13 Yesterday, 03:20 PM
Last Post: MikePhua
  Komatsu D37 Track Tension Loss and Adjuster Cylinder Repair MikePhua 0 10 Yesterday, 03:13 PM
Last Post: MikePhua
  Cone Crusher Performance Issues and Practical Troubleshooting MikePhua 0 10 Yesterday, 03:11 PM
Last Post: MikePhua
  Komatsu PC120-6 Hydraulic Power Loss After Warm-Up MikePhua 0 10 Yesterday, 03:08 PM
Last Post: MikePhua
  Rebuilding a Komatsu D155AX-6 Dozer with the Right Technical Resources MikePhua 0 9 Yesterday, 02:58 PM
Last Post: MikePhua
  Komatsu PC600LC-8 Heavy Black Smoke During Operation MikePhua 0 10 Yesterday, 02:36 PM
Last Post: MikePhua
  Diagnosing and Resolving Crankshaft Position Sensor Issues in Caterpillar 299D MikePhua 0 7 Yesterday, 02:33 PM
Last Post: MikePhua
  Diagnosing Brake Failure on the Komatsu D65E-7 Dozer MikePhua 0 10 Yesterday, 02:33 PM
Last Post: MikePhua
  Fuel Starvation and Performance Issues in the Caterpillar IT28G MikePhua 0 6 Yesterday, 02:32 PM
Last Post: MikePhua
  Komatsu PC78 Idle Drop During Digging and Monitor Panel Diagnostics MikePhua 0 11 Yesterday, 02:30 PM
Last Post: MikePhua

Forum Jump:


Users browsing this thread: 1 Guest(s)