Insufficient machine power is a common but high-level fault in construction machinery. As a mechanic, this fault can be challenging to diagnose accurately on-site. The simplest cause is often fuel circuit blockage or clogged filters.

However, accurate diagnosis under on-site conditions requires substantial practical knowledge and experience. Based on personal experience, the following summary may serve as a reference for industry peers.

In general, insufficient machine power arises from either:

1. Engine power deficiency,

2. Overload in the machine’s operational system,

3. Or a combination of both.

I. Engine Power Deficiency

1. Engine cannot reach rated RPM under maximum load

• Symptoms: Engine speed below rated RPM, sometimes accompanied by heavy black smoke or even stalling.

• Steps to check:

  • Verify if the machine is overloaded.

  • Reduce load to standard specifications; if the issue is alleviated, overload is the cause.

  • Note: Arbitrary increase of hydraulic system pressure also constitutes overload.

  • If pressure is returned to standard but engine power is still insufficient, consider whether the hydraulic flow is too high. For variable hydraulic systems, flow and pressure are inversely proportional: high flow within pump specifications requires lower pressure; otherwise, the engine will overload.

  • Caution: Adjusting hydraulic pump flow without a flow meter or specifications may lead to incorrect settings and further issues.

2. Engine under full throttle, maximum load, low machine action speed

• Symptoms: Engine load feels light, RPM may exceed rated speed, but machine action is slower than factory specifications.

• Cause: Machine load is insufficient to utilize maximum engine performance.

3. Performance parameter reference

• Testing must be based on machine factory performance parameters, as there is no direct engine power measurement device installed.

• Examples of parameters to measure:

  • Mining trucks: maximum speed under full load

  • Wheel loaders: lift and unload time under specified conditions

  • Bulldozers: travel speed unloaded

  • Excavators: full cycle action times

• Measurement requires stopwatch timing for accuracy.

4. Turbocharged engine power testing

• Method: Measure instantaneous maximum intake boost pressure, record data to evaluate engine power output.

II. Overload in Machine Operational System

1. Symptoms of system overload

• Engine produces black smoke, unstable RPM, tendency to stall.

• Machine performance parameters exceed factory specifications (hydraulic system, torque converter, or operational abnormality).

2. Observations

• During testing, machine action parameters may drop only slightly.

• Accurate measurement requires stopwatch timing of cycles.

III. Combined Engine Performance Decline and System Overload

1. Symptoms

• Engine stalls during testing, often without heavy black smoke.

2. Troubleshooting

• Determine which hydraulic circuit causes stalling by elimination method.

• Frequently, variable hydraulic system circuits are involved, often due to variable pump malfunction, preventing minimum flow adjustment.

• Less common in fixed displacement pump systems, where the typical issue is flow reduction.

3. Measuring machine circuit performance

• Machines of the same tonnage generally have similar performance parameters.

• Measurement can be done if the machine travels straight; if drifting occurs, additional diagnostic steps are required.

Notes

• These methods are based on practical experience with used machines or post-repair testing, not blindly copying new machine specifications.

• Accurate diagnosis requires knowledge of engine, hydraulic system, and machine operational parameters, combined with systematic observation and testing.