Detailed Analysis and Troubleshooting Guide for Hitachi EX120-2 No-Start Issue: Fuel System and Engine Diagnostics

[MikePhua]

Heavy machinery like the Hitachi EX120-2 excavator can sometimes face stubborn starting problems that challenge even experienced operators and mechanics. When such a machine cranks but fails to start, particularly after a period of sitting idle, a systematic understanding of the fuel system, injection timing, and electronic controls is crucial for diagnosis and repair. This article explores the key causes of no-start conditions in the Hitachi EX120-2, diagnostic steps taken by operators, technical concepts related to the fuel system, and practical recommendations to resolve these problems effectively.
Background and Scenario
A common scenario is a Hitachi EX120-2 that ran fine previously, then sat unused for about two weeks, after which it cranks without starting and shows no smoke emissions. The initial suspicion in many such cases is fuel delivery failure or air ingress causing loss of prime in the fuel system. Operators may observe excessive bubbles during bleeding attempts and inconsistent fuel flow. Despite replacing fuel lines and water separator seals, the issue may persist with symptoms including blue/white smoke and occasional brown/black puffs during cranking but no sustained engine ignition.
Understanding Key Components and Terms

• Fuel System and Prime: The fuel system consists of the fuel tank, fuel lines, water separator, fuel filters, injection pump, and injectors. "Priming" means removing air from the system to allow continuous fuel flow.
  
• Injectors: Deliver atomized fuel into the combustion chamber. Proper spraying patterns are essential for combustion.
  
• Glow Plugs: Heat the combustion chamber at startup, especially critical in cold conditions.
  
• Fuel Shut-Off Lever: Controls fuel supply; must be free and functional to allow starting.
  
• Injection Pump (Zexel type in this machine): Supplies fuel to injectors at precise timing and pressure; critical for ignition and performance.
  
• Crank vs. Start: Cranking indicates the engine is physically turning over, whereas starting means the engine igniting and running steadily.
  

Diagnostic Process

1. Checking Fuel Delivery:
   • Bleeding the fuel system to remove air delays or bubbles indicating leaks or seal failures.
     
   • Replacing suspect fuel lines and inspecting fuel separator seals for leaks or blockage.
     
   • Checking the banjo bolts feeding fuel and return lines for debris or damage.
     
   • Observing mist spray from injectors by removing and testing them individually to ensure atomization.
     
2. Smoke Analysis During Cranking:
   • Blue/white smoke often signals fuel presence but incomplete or poor combustion, sometimes caused by injection timing errors or flooding.
     
   • Occasional black/brown smoke can indicate combustion inefficiency or excess fuel.
     
3. Intake and Glow Plug Checks:
   • Using a heat gun at the air intake verifies that cold starts are not hampered by temperature issues.
     
   • Testing operation of glow plugs by disconnecting and checking for engine response.
     
   • Spraying brake cleaner into the intake to test for engine reaction to an alternative combustible substance helps separate fuel delivery issues from engine mechanical problems.
     
4. Fuel Shut-Off Lever Functionality:
   • Confirming that the shut-off lever is free and not mechanically stuck ensures fuel flow is not inadvertently restricted.
     
5. Considering Injection Timing:
   • Injection timing affects when fuel is delivered to the combustion chamber relative to piston position. A mis-timed injection pump can cause cranking without starting as fuel may be injected too early or late for ignition.
     
   • Timing issues may arise from mechanical slippage, pump setting errors, or component wear, sometimes occurring during periods of inactivity.
     

Real-World Examples and Related Insights

• Operators of similar Hitachi models sometimes encounter starting failures due to air ingress in fuel lines, which can mimic fuel starvation even if the tank is full and fuel system parts appear intact. Meticulous fuel system bleeding and line replacement solve many such issues.
  
• A separate case involved injection pump failure or timing drift on an Isuzu 4BD1T engine (the same engine in this excavator), where timing readjustment and pump recalibration restored starting capability.
  
• Some mechanics report that engines unwilling to start but respond to brake cleaner injected into the intake suggest fuel delivery rather than engine mechanical failure.
  

Recommendations and Solutions

• Thoroughly check and replace old or suspect fuel lines between the fuel tank and water separator to prevent air leaks.
  
• Pressure test and reseal the water separator and fuel filter connections to ensure airtight fuel delivery.
  
• Confirm injector spray pattern by removing and testing individual injectors; replace or service any with weak or irregular spray.
  
• Confirm glow plug condition and wiring to eliminate starting heating issues.
  
• Verify the fuel shut-off lever is freely operating and lubricated as necessary.
  
• If fuel system checks are inconclusive, inspect and potentially adjust the injection pump timing. This adjustment often requires professional tools or service manual instructions.
  
• Consider consulting engine and fuel system diagnostic manuals for detailed timing check and adjustment procedures, especially for Zexel injection pumps.
  
• Regular preventive maintenance, including fuel filter changes, clean fuel storage, and injector servicing, minimizes future issues.
  
• In some cases, using a heat source like a heat gun on the intake in cold climates can assist in diagnosing temperature-related starting problems.
  

Supplemental Advice

• Document all troubleshooting steps and results to correlate symptoms with fixes.
  
• If no improvement is seen, professional diagnostic equipment such as electronic injection pump testers or engine analyzers may be needed.
  
• Maintain clean fuel storage and pre-filtering to reduce contamination and water buildup.
  
• Training for operators and technicians on bleeding procedures and fuel system inspection enhances early issue detection.
  

Terminology Explained

• Banjo Bolt: A hollow bolt with a hole allowing fluid flow, commonly used in fuel and hydraulic lines.
  
• Injection Timing: The timing at which fuel is injected into the combustion chamber relative to piston position.
  
• Fuel System Prime: The process of removing air and filling the fuel system with fuel to ensure continuous flow.
  
• Atomization: The process of breaking fuel into a fine spray for efficient combustion.
  
• Fuel Shut-Off Lever: A mechanical lever that stops fuel flow to the engine for emergency or maintenance purposes.
  

By systematically addressing these areas with careful inspection, testing, and adjustment, operators and technicians can diagnose and resolve starting issues in the Hitachi EX120-2 excavator. This ensures reliable machine deployment and reduces costly downtime in demanding construction and industrial environments.