TCM FCG15-3L Cranks but Won’t Start: A Comprehensive Troubleshooting Guide

[MikePhua]

Key Diagnostic Terms to Know

• Cranking: The starter turns the engine, indicating battery and starter motor are functional.
  
• ECM (Engine Control Module): The computer that manages ignition timing, fuel, and sensor data.
  
• Crankshaft & Camshaft Sensors: Electronic parts that report engine position to the ECM; essential for proper ignition.
  
• Propane Regulator / Vaporizer: Reduces tank pressure and vaporizes liquid propane for safe fuel delivery.
  

Case Overview and Problem Background
The forklift cranks normally but fails to fire. Attempts to pinpoint the cause have included:

• Replacing spark plugs
  
• Testing and swapping crank and cam sensors
  
• Checking ECM functionality
  
• Replacing the propane regulator
  

Despite these steps, the engine still refuses to catch and run. These symptoms suggest a more intricate issue beyond initial guesswork.

Expanded Diagnostic Checklist

• Fuel Path Verification:
  • Confirm sufficient propane level in tank and correct tank orientation.
    
  • Examine coupler integrity—ensure proper sealing and that O-rings or quad rings aren’t displaced.
    
  • Inspect fuel solenoid function; it must allow fuel flow when energized.
    
• Ignition and Timing Confirmation:
  • Spark plugs are new but test for spark quality with a tester—blue spark indicates healthy ignition, yellow or weak spark indicates degradation.
    
  • Investigate ignition coils and wiring harness integrity, including fuses and onboard relays.
    
• Power Distribution and Interlocks:
  • Locate and inspect relays—specifically ones supplying power to ignition coils, ECM, and LPG injector circuits.
    
  • Verify the neutral safety switch and interlock systems aren’t preventing startup.
    
• Sensor and Control Accuracy:
  • Even though sensors were replaced, double-check sensor wiring for breaks, shorts, or corrosion.
    
  • Explore available OBD2 diagnostic connectors; code reading can guide toward ECM or sensor faults.
    
• Compression and Engine Health:
  • Conduct a compression test; low compression impedes ignition even if fuel and spark are both present.
    

Troubleshooting Recommendations

• Fuel System Focus:
  • Ensure tank valve is fully open and that LPG flows freely.
    
  • Examine filter condition—propane components like ethyl mercaptan or tank contaminants can clog regulators or injectors.
    
• Electrical Flow Validation:
  • Trace power circuits from battery to key ignition switch, ECM, and ignition coil. Voltage absence at any point indicates broken or faulty wiring or relay.
    
• Add Diagnostic Tools:
  • Use an OBD2 scanner to retrieve error codes related to fuel injection, ignition timing, or valve operation.
    
• Testing Under Load:
  • Attempt a controlled start with minimal load (e.g., in neutral, no auxiliary systems engaged) to simplify troubleshooting.
    

A Mini-Story from the Shop
A local operator found their forklift unresponsive even after major troubleshooting. It turned out to be a tiny issue—a mis-seated quad ring in the propane coupler. Without proper seal, fuel never reached the engine. Reseating it fixed the issue instantly, reminding everyone that even small details can stop an engine cold.

Summary of Steps in Listed Form
Here’s a consolidated list to follow in sequence:

• Confirm propane tank is full and mounted correctly.
  
• Inspect coupler seals and ensure tight insertion.
  
• Check fuel solenoid, regulator, and filter function.
  
• Test for spark with new plugs and use a spark tester.
  
• Verify relays powering ignition, ECM, and injector circuits.
  
• Check neutral safety and interlock switch positions.
  
• Use diagnostic tool to read codes (if available).
  
• Conduct compression test to confirm mechanical integrity.
  
• Trace wiring from battery to ignition and sensors for continuity.
  
• Reattempt start with only essential systems active.
  

Conclusion
When a TCM FCG15-3L forklift cranks but won’t start, a structured elimination process—beginning with fuel delivery and progressing through ignition, electrical, and mechanical systems—can save time and frustration. Start with basics like tank connection and spark quality, then move to system controls and electronic diagnostics. Often the issue is something small but critical. Let me know if you'd like help mapping the wiring harness or interpreting OBD2 codes specific to your model!