Troubleshooting for the PC200-6A excavator being stuck

In July 2003, a PC200-6A hydraulic excavator experienced a stalling problem while working in the suburbs of Boxing. That is, unstable engine speed occurs during operation. When the load increases, the engine speed drops significantly, accompanied by overall weakness and slow operation of the machine. There are two causes and locations for this malfunction: one is the engine and its electronic control system; The other one is the servo system of the pump (which includes hydraulic components and the pump controller in the electrical system).

In accordance with the principle of starting with the easier tasks and moving on to the more complex ones, and considering that the time for replacing the fuel filter element of this machine had expired, the fault was eliminated after the fuel filter element was replaced. After that, the malfunction occurred again. Then, the fuel tank was inspected. There were no obvious suspended particle impurities in the fuel, and the fuel color was relatively transparent. Based on this, further maintenance is required.

First, the fuel pump of the fuel system was calibrated, and no abnormalities were found.

The on-site detection data is

Engine start-up :n=990r/min(idle speed); n=2140r/min(high speed). All the above data are in the A state of H mode and the automatic deceleration switch is off.

Governor :C03 convex = 10Ω, C13 convex = 10Ω.

Water temperature sensor :P07 at normal temperature =32.2kΩ, after startup, P07=4.56kΩ.

Rotational speed sensor :E07 convex =900Ω.

Both exhaust and oil consumption are shown as normal.

Hydraulic system: The front pump pressure PF=343kgf/cm ² and the rear pump pressure PR=348kgf/cm ² are normal. The output pressure of LS shuttle adjustment PLs=310kgf/cm2>3/5P(P-P Ls is normal within 29±10kgf/cm2).

The maximum pressure at the ends of the servo pistons of the front and rear pumps is PenR=170kgf/cm ² and PenF=173kgf/cm ² =P/2(normal).

When the control handle is in the median position, PPCEPC=30kgf/cm ² and PLSEPC=30kgf/cm ² (normal within 336kgf/cm ²).

When re-digging, PLSEPC=1kgf/cm ², that is, at this time, the LSEPC solenoid valve is close to closing (normal).

The above data indicate that the servo system is normal. Based on this, it can be judged that the PC valve can be appropriately adjusted to observe its effect. No obvious effect was observed after unscrewing the PC valve three times (at 30 degrees, 90 degrees, and 180 degrees). After conducting the above tests and high-speed operations, it can be determined that the cause of the fault does not lie in the hydraulic system or the mechanical and electrical parts of the engine.

The fuel pipeline was inspected again and no obvious abnormal conditions were found. Finally, by reviewing the occurrence and development process of the fault, it was learned that replacing the fuel filter element could completely eliminate the fault in a short period of time. Based on this, the fuel coarse filter was short-circuited for a test run, and the fault was eliminated. When the fuel coarse filter was connected to the fuel pipeline again, the fault occurred. Based on this, it can be determined that the faulty part lies in the fuel coarse filter.

When the fuel coarse filter was removed and sawn open, it was found that there was a layer of viscous, unknown grease adhering to the surface of the filter paper. This was the crux of the problem. From this, it can be inferred that when refueling this machine, there is a gel-like grease mixed in (which does not change the color of the fuel). This kind of grease cannot pass through the filter paper and can only be adsorbed on the surface of the filter paper, blocking the filter element.

After learning about this situation, the user carefully cleaned the fuel tank and replaced the fuel filter element to completely eliminate the fault.

From the above analysis, it can be seen that not all the indicators of fuel can be judged by visual observation. To diagnose faults, one should do it personally and experience it firsthand. When dealing with faults, one should have a clear mind, keep in mind questions, learn more about the situation, and not let go of any clues. Only in this way can one avoid detours and do unnecessary work.