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A Komatsu PC160LC-7K excavator presented with two persistent and interrelated problems: poor engine starting when hot and abnormal hydraulic load behavior. These issues developed gradually over approximately 1,000 operating hours and became increasingly disruptive. While cold starts were reliable—even in extreme winter conditions—the engine struggled to restart after prolonged operation in hot environments. Simultaneously, the hydraulic system began imposing excessive load on the engine when idle, sometimes stalling it entirely.

Engine Starting Trouble: Heat-Related Fuel Pump Behavior

The engine exhibited the following symptoms:

  • Cold starts were smooth, even at –20°C
  • Warm starts after short idle periods were successful
  • Hot starts after extended operation were difficult, with knocking sounds and delayed ignition
  • No visible smoke or power loss during normal operation

These signs point toward thermal degradation of the fuel injection pump. As the pump heats up during long operation, its internal tolerances may shift, reducing fuel delivery pressure and delaying ignition. This is especially common in older mechanical pumps or those with worn plungers and seals.

While valve clearance was suspected, it was deemed unlikely to cause such heat-dependent behavior. A rebuild or replacement of the injection pump is often the definitive solution, though some operators have reported temporary improvement by adjusting timing or replacing the fuel solenoid.

Hydraulic Load Anomaly: LS Pressure and Control Valve Contamination

The hydraulic system showed a more complex failure mode:

  • When hot, the system imposed high load on the engine even at idle
  • The load disappeared when the swing joystick was lightly touched
  • Releasing the joystick caused the load to return, sometimes stalling the engine
  • When cold, the swing motor failed to engage, but the boom could move freely
  • Metal debris was found in the suction filter during hydraulic oil change

This behavior suggests a malfunction in the load-sensing (LS) pressure circuit, specifically within the control valve’s neutral drain throttles. These throttles regulate LS pressure when no function is engaged. If their fine mesh filters become clogged with debris, LS pressure remains elevated, causing the pump to upstroke unnecessarily and overload the engine.

Technicians familiar with this issue have identified two critical throttles in the center section of the control valve. When clogged:

  • LS pressure fails to drain in neutral
  • The pump remains activated even without joystick input
  • Engine cranking becomes difficult due to hydraulic resistance
  • Pressure readings on the monitor may exceed 120 bar when hot (normal cold value: ~30 bar; maintenance threshold: ~70 bar)

In extreme cases, even a rebuilt 4-cylinder Cummins engine may fail to start if LS pressure remains high.

Contamination and Long-Term Damage

The presence of metal debris in the suction filter indicates internal wear or component failure—possibly from a prior hydraulic event. This contamination can damage spool valves, throttle filters, and pressure regulators. Even after cleaning, residual particles may continue to interfere with valve operation.

Operators are advised to:

  • Flush the hydraulic system thoroughly
  • Replace all filters, including pilot and return filters
  • Inspect and clean throttle filters in the control valve
  • Monitor LS pressure during cold and hot operation
  • Consider replacing damaged valve sections if symptoms persist

Field Case and Resolution Timeline

One technician reported that resolving a similar issue took over a week. After cleaning the throttles and restoring LS pressure control, the machine still exhibited minor irregularities due to valve section damage. Two of his clients ultimately replaced damaged control valve sections to fully restore performance.

Final Thoughts

The Komatsu PC160LC-7K’s dual-system failure highlights the interplay between hydraulic pressure regulation and engine behavior. While the fuel injection pump may be the root cause of poor hot starts, the hydraulic system’s inability to drain LS pressure in neutral creates excessive load that compounds the problem. Contamination from prior failures further complicates diagnosis. With careful pressure monitoring, throttle inspection, and system flushing, these issues can be addressed—restoring the excavator’s reliability and performance.

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