How to Diagnose and Fix a Komatsu 267 That Dies When Turning the Key to the Start Position

[MikePhua]

Experiencing a situation where a Komatsu 267 engine dies or cuts out immediately upon turning the key to the start position can be frustrating and disruptive. This detailed guide explains the common causes, diagnostic steps, terminology, and practical solutions to effectively troubleshoot and resolve this problem, ensuring reliable engine starting and operation.
Understanding the Symptom
When the key is turned to the start position, the engine cranks but then immediately dies or shuts off. This indicates that the engine ignition or fuel supply system is interrupted or insufficient during cranking and startup. The problem could stem from electrical, fuel delivery, safety interlocks, or mechanical issues.
Key Terminology

• Starter Circuit: The electrical path that powers the starter motor to crank the engine.
  
• Fuel Shutoff Solenoid: An electromagnet-controlled valve that allows fuel flow to the engine when energized.
  
• Ignition Switch: Controls power to the starter, fuel solenoid, and ignition system.
  
• Battery Relay (BAT RL): Relay controlling battery power distribution, including to the starter and fuel controls.
  
• Ground Strap: Electrical grounding wire ensuring stable current flow and system operation.
  
• Kill Switch/Stop Switch: Safety device or circuit that cuts power to shut off the engine.
  

Common Causes

• Faulty Fuel Shutoff Solenoid: If the solenoid does not energize, fuel flow stops as soon as cranking begins, causing the engine to die.
  
• Weak Battery or Poor Electrical Connections: Low voltage may allow cranking but insufficient power to keep solenoids energized.
  
• Bad Ignition Switch or Relay: Interrupted power to critical systems during crank.
  
• Loose or Damaged Wiring and Connections: Intermittent or broken wiring to solenoid or starter circuit.
  
• Faulty Stop or Kill Switch: Immediately cuts power when attempting to start.
  
• Safety Interlock Malfunction: Some machines have operator presence or transmission range interlocks preventing start.
  
• Grounding Issues: Bad ground connection causing unstable electrical systems.
  

Step-by-Step Diagnostic Guide

1. Check Battery Condition and Connections
   • Measure battery voltage (should be near 12.6 volts at rest).
     
   • Inspect battery terminals for corrosion and tightness.
     
   • Ensure ground strap between battery negative and chassis is secure.
     
2. Inspect Fuel Shutoff Solenoid
   • Listen for a “click” sound on turning key to ON/start position (solenoid energizing).
     
   • Use a multimeter to check for voltage at solenoid terminals during crank — voltage should be present.
     
   • If no voltage, check wiring continuity and ignition switch output.
     
   • If voltage present but no solenoid activation, test or replace solenoid.
     
3. Verify Ignition Switch and Relay Operation
   • Test ignition switch for proper operation with multimeter or test light.
     
   • Check battery relay function by swapping with a known good relay or testing contacts.
     
   • Inspect relay socket and connectors.
     
4. Examine Wiring Harness and Connections
   • Look for damaged wiring, loose connectors, or broken pins especially around battery, ignition switch, solenoid, and relay.
     
   • Repair or replace faulty wiring.
     
5. Check Stop/Kill Switches and Safety Interlocks
   • Test for continuity and correct operation of any stop or kill switches.
     
   • Verify operator presence or transmission range switches are not falsely preventing start.
     
6. Test Starter Circuit
   • Confirm starter motor receives full voltage and cranks properly.
     
   • Inspect starter solenoid and wiring.
     

Additional Tips and Solutions

• Clean and tighten all battery and ground connections regularly to ensure stable electrical flow.
  
• Use dielectric grease on connectors to prevent corrosion and improve contact.
  
• Replace fuel solenoids proactively if aged or showing intermittent function.
  
• Keep a spare starter relay and solenoid for quicker field replacement.
  
• Consider testing with a known good battery to rule out weak battery problems.
  
• Check for engine mechanical issues separately if electrical and fuel systems are verified.
  

Real-World Case Example
A Komatsu 267 operator struggled with the engine dying immediately on startup. Inspection revealed the fuel shutoff solenoid was not receiving any voltage during cranking because a wire near the ignition switch had worn insulation and intermittent breakage. After repairing the wiring and testing the solenoid’s activation, the engine started and ran normally. The user emphasized the importance of thorough wiring inspection and keeping spare solenoids available.
Summary List: Essential Checks for Engine Dies on Start Key Turn

• Battery voltage and connections
  
• Ground strap integrity
  
• Fuel shutoff solenoid voltage and operation
  
• Ignition switch functionality
  
• Battery relay presence and continuity
  
• Wiring harness condition and connectors
  
• Stop/kill switch and safety interlock operation
  
• Starter motor voltage and operation
  

Conclusion
Engines that die when turning the key to the start position often suffer from interrupted fuel supply or electrical faults, most commonly involving the fuel shutoff solenoid, battery, ignition switch, or wiring. Systematic electrical and fuel system diagnostics combined with proper maintenance practices such as secure connections and testing solenoid functionality can quickly resolve these startup failures.