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:
Engine power deficiency,
Overload in the machine’s operational system,
Or a combination of both.
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.
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.
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.
Method: Measure instantaneous maximum intake boost pressure, record data to evaluate engine power output.
Engine produces black smoke, unstable RPM, tendency to stall.
Machine performance parameters exceed factory specifications (hydraulic system, torque converter, or operational abnormality).
During testing, machine action parameters may drop only slightly.
Accurate measurement requires stopwatch timing of cycles.
Engine stalls during testing, often without heavy black smoke.
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.
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.
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.
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