Intermittent Rough Running on a Komatsu PC220LC‑6

[MikePhua]

Komatsu is a global heavy‑equipment giant founded in Japan in 1921, now one of the world’s top manufacturers of construction machines. The PC220LC series is a mid‑sized excavator widely used in civil construction, thanks to its balanced power and reach. The PC220LC‑6 in particular offers about 158 hp (according to spec listings) with an operating weight around 23,480 kg.

Symptoms and Problem Description
The machine in question starts and runs, but runs rough intermittently. Sometimes it vibrates, hesitates, or stumbles under load, but at other times it runs smoothly. There’s no consistent pattern — the issue comes and goes, making it hard to pinpoint.

Potential Causes
Based on experience and common failure modes, there are several likely culprits:

• Fuel system contamination or air: If there's dirt or water in the fuel, or air in the lines, it can cause rough running.
  
• Injector problems: One or more fuel injectors might be dirty, partially clogged, or malfunctioning, leading to intermittent misfire or rough combustion.
  
• Fuel pump issues: The high-pressure injection pump might not be delivering steady pressure, or its internal wear could be inconsistent, causing poor fuel delivery.
  
• Sensor or electronic control faults: If the machine has control modules or sensors (throttle position sensor, fuel pressure sensor, etc.), intermittent faults or poor readings could make the engine run poorly.
  
• Engine mechanical issues: Things like worn piston rings, low compression in one or more cylinders, or valve problems could cause roughness under load.
  
• Hydraulic load coupling: When the hydraulics draw a lot of load (boom, swing, digging), the engine could be starved or choked, especially if fuel delivery or air intake is marginal.
  

Diagnostic Steps to Try
To isolate and identify the root cause, you could follow these steps:

1. Inspect the Fuel
   • Drain a sample from the fuel filter or water separator and check for water, sludge, or contaminants.
     
   • Replace the fuel filter if it hasn’t been changed recently, and bleed the fuel system carefully to remove air.
     
2. Check Injectors
   • Run a leak-down test on each injector (if you have the tools) to see if any are leaking or weak.
     
   • Consider having injectors professionally tested/cleaned or replaced if they’re questionable.
     
3. Evaluate the Fuel Pump
   • Monitor fuel pressure at the pump output under load (if you have a gauge).
     
   • Listen for unusual noises from the pump that could indicate internal wear.
     
4. Scan for Engine Faults
   • If equipped, pull diagnostic codes or use a scan tool to check for sensor faults.
     
   • Inspect wiring harnesses, connectors, and sensor mounting for signs of damage or poor connection.
     
5. Do a Compression Test
   • Perform a compression test on each cylinder to verify that they’re within spec. Low compression could indicate engine wear or valve problems.
     
6. Load Testing
   • Run the machine under typical working load (digging, swinging) and note when the roughness appears.
     
   • Compare engine RPM, hydraulic flow demand, and any changes in vibration or smoke.
     

Real‑World Insights and Stories

• One owner of a similarly sized Komatsu machine reported that after replacing the fuel filter and not properly bleeding the lines, the machine stuttered badly under load until he re-bleeded the system thoroughly.
  
• Another technician noted that in older Komatsu machines, injector tip wear is surprisingly common: even if an injector seems “okay” when cold, its performance can degrade under high demand, causing occasional rough spots.
  
• On Reddit, users have mentioned issues with Komatsu control modules or solenoids causing erratic engine behavior — once a faulty solenoid was replaced, the roughness disappeared.
  

Solutions and Recommendations
Here are practical fixes and steps to resolve or mitigate the problem:

• Replace the fuel filter and water separator, bleed the system thoroughly, and check for water contamination.
  
• Test or replace fuel injectors if they’re suspected; use OEM or quality aftermarket injectors.
  
• Check the fuel pump’s health: inspect, test pressure, and consider replacement if worn.
  
• Use a diagnostic tool to scan for ECM or sensor faults; repair or replace faulty wiring/sensors.
  
• Perform a compression test on each cylinder to assess engine mechanical health.
  
• Ensure the machine is not starved of fuel or air under hydraulic load; check intake filters and fuel delivery.
  

Maintenance Tips to Prevent Recurrence

• Change the fuel filter and water separator at recommended intervals (or more often if working in dirty conditions).
  
• Use clean, high-quality fuel, and always drain water from the fuel system.
  
• Periodically test injectors or have them cleaned to maintain performance.
  
• Keep wiring and sensors clean and secure to avoid intermittent issues.
  
• Monitor engine and hydraulic behavior under load regularly to catch problems early.
  

Technical Terms Explained

• Injector (Fuel Injector): A device that sprays fuel into the combustion chamber; if clogged or worn, it can cause rough running.
  
• Compression Test: A test to measure the pressure each cylinder can build, indicating the condition of rings, valves, and integrity.
  
• Bleeding: The process of removing air from the fuel or hydraulic system by manually purging lines.
  
• Solenoid: An electrically controlled valve, often used in fuel or hydraulic systems to regulate flow.
  
• Fuel Pump Pressure: The amount of pressure the fuel pump generates to deliver fuel to injectors; critical for proper engine operation.
  

Conclusion
An intermittent rough-running Komatsu PC220LC‑6 is frustrating but usually traceable with a systematic approach. Most often, it’s about fuel delivery (filter, injectors, pump), but engine mechanical issues or sensor faults can also be the culprit. By methodically inspecting, testing, and, if necessary, replacing suspect parts, you can restore smooth performance. Proper maintenance and vigilance under working load will help prevent the issue from coming back.