Three cases of diesel fuel injection pump failure in construction machinery

The fuel injection pump is an important component of the diesel engine's fuel system. Its working condition directly affects the power performance, economy and reliability of the diesel engine. During the maintenance, some repairmen did not pay much attention to the fuel injection pump, which led to some artificial malfunctions. The following are only three examples for reference when looking for faults.

A ZL50CII type loader was equipped with a 6135K-9a diesel engine. There was no obvious fault when idling, but a "putt-putt-putt-" sound occurred as soon as it accelerated, and the color of the exhaust smoke was either white or black, extremely unstable. At first, it was thought that the fuel injection timing was incorrect, but after readjusting the fuel injection timing, the fault persisted. The low and high pressure oil circuits were inspected again, but no problems were found. Finally, when the fuel injection pump was removed, it was found that the lock nut at the end of the fuel injection advance device had become loose, the keyway between the fuel injection advance device and the camshaft of the fuel injection pump had widened due to wear, and the thickness of the semi-circular key was less than half of its original size. After re-milling the grooves and re-assembling the keys, the fault phenomenon disappeared. It is understood that the fuel injection pump of this machine was repaired not long ago. The direct cause of this malfunction is that the maintenance personnel did not tighten the lock nut to the specified torque when installing the extended fuel injection advance device. As a result, when the engine was running at a variable speed, the loose fit between the fuel injection advance device and the camshaft accelerated the wear of the keyway and semi-circular key, thereby causing unstable fuel injection timing.

(2) The model of the fuel injection pump of a 6135K-12C diesel engine used on a TL180 bulldozer is BH6B100YS490. During a major engine overhaul, both the fuel injection pump and the fuel injector were calibrated on the test bench. After the engine was running-in, the bulldozer was put into earthwork operations. However, due to the engine's weak power, it was unable to operate. Moreover, when the engine was unloaded and the accelerator was suddenly pressed, poor acceleration was felt. After inspection, it was found that the engine and fuel injection timing were all normal, there were no air leaks in the fuel lines, and the governor, fuel injection pump, low-pressure and high-pressure fuel lines, etc. were also fine. Therefore, it is suspected that the rated working condition fuel volume might have been set too low during pump calibration. So, the fuel injection pump was removed and recalibrated on the test bench. It was found that it was indeed the pump calibrator who had mistakenly lowered the rated working condition fuel volume of the fuel injection pump by 6mL per 200 times. After recalibration, the fuel injection pump was reinstalled. During the test run, the operation was normal and powerful.

(3) A W4-60C excavator equipped with an F6L912 diesel engine suddenly stalled on its way to the construction site. It tried to start several times but failed to do so. Observing the exhaust situation, no smoke was seen. It was initially determined that there was a fault in the oil circuit. During the inspection, a manual pump was used to pump the oil. The result was that the oil output was good and there was no air leakage or blockage in the oil circuit. When the speed control handle is swung, the fuel injection pump fuel volume adjustment pull rod does not respond. When the governor was disassembled, it was found that the connection between the fuel supply pull rod and the speed control lever had become loose and the pin had broken. Reconnect the fuel supply pull rod to the speed control lever and lock it with a new pin. If it starts up quickly when initiated, it indicates that the fault has been eliminated. The cause of this malfunction is that the maintenance personnel did not replace the new pins as required when assembling the governor, but still used the original removed and cracked pins as new ones, resulting in the pins breaking and the connection between the fuel supply pull rod and the speed control lever loosening, thus causing the failure to start.