As one of the core components of a diesel engine, the fuel injector plays a decisive role in the overall performance of the equipment. Its working condition directly determines the engine’s power output, fuel efficiency, emission standards and operational stability. To match the fuel mixing and combustion requirements of diesel engines, a qualified fuel injector must meet strict operating standards: stable injection pressure, standard injection stroke and optimal spray cone angle. In addition, the injector needs to cut off fuel supply instantly after finishing injection to avoid fuel dripping, which is a key standard for normal operation.
Professional fuel injector test benches are the standard equipment to inspect injector performance and judge component damage. It is worth noting that all parts of the common rail system are highly sensitive to moisture in the fuel system, especially precision components like fuel injectors. These delicate valve assemblies rely entirely on diesel fuel for lubrication during operation. Once water enters the fuel system, it will cause component rusting, insufficient lubrication and a series of subsequent mechanical failures, seriously affecting the service life and working efficiency of the injectors.
In daily engine operation, fuel injectors are prone to multiple typical faults due to poor fuel quality, long-term wear and improper maintenance. Below we sort out the most common failures, corresponding symptoms and root causes for your reference and daily troubleshooting.
1. Poor Fuel Atomization
Failure Symptoms: The diesel engine suffers from insufficient power, black exhaust smoke and abnormal operating noise during operation.
Fault Analysis: This problem mainly stems from abnormal internal wear and parameter deviation of the injector. Low injection pressure, carbon deposits on nozzle holes, and wear or elastic fatigue of the spring end face will cause the injector to open early and close late. This irregular injection process leads to poor fuel atomization.
Large unatomized diesel droplets cannot be fully burned in the cylinder. The residual fuel will flow down the cylinder wall into the oil pan, raising the oil level and reducing lubricating oil viscosity. This not only worsens the engine’s lubrication condition but also easily triggers severe mechanical accidents such as bearing burning and cylinder scoring.
2. Stuck Needle Valve
Failure Symptoms: The engine runs jittery with obvious power loss; in severe cases, the engine fails to start normally.
Fault Analysis: Impurities in unqualified diesel, including moisture and acidic substances, will corrode the injector needle valve and cause jamming. Long-term operation will also damage the sealing cone surface of the needle valve, allowing combustible gas in the cylinder to penetrate the matching surface and form hard carbon deposits. The accumulated carbon will lock the needle valve completely, disabling the fuel injection function of the injector and causing the corresponding cylinder to stop working.
3. Wear of Needle Valve and Guide Hole Surface
Failure Symptoms: Continuous power attenuation, difficult cold start, and complete startup failure in serious scenarios.
Fault Analysis: The needle valve moves back and forth frequently inside the guide hole during engine operation. Impurities mixed in diesel fuel will accelerate the wear of the guide surface, resulting in enlarged matching gaps and scratch marks on the surface. These damages will increase internal fuel leakage of the injector, lower injection pressure, reduce fuel delivery and delay injection timing. The above problems will directly lead to difficult engine startup. If the injection delay is too serious to support normal operation, the needle valve assembly needs to be replaced in time.
4. Nozzle Fuel Dripping
Failure Symptoms: White exhaust smoke and difficult startup when the engine is cold; the smoke turns black as the engine warms up, accompanied by significantly increased fuel consumption.
Fault Analysis: The sealing cone surface of the needle valve body bears frequent strong impact from the needle valve and continuous scouring of high-pressure fuel during long-term operation. Gradual wear and pitting on the cone surface will damage the airtightness, causing fuel dripping after injection.
When the engine temperature is low, the leaked fuel cannot be fully burned, producing white smoke; as the engine temperature rises, the unburned fuel decomposes to form black smoke. During inspection, check whether the needle valve moves flexibly and whether the cone surface is intact and well-sealed. Severe wear and poor airtightness require immediate replacement of the nozzle assembly.
5. Excessive Fuel Return Volume
Failure Symptoms: Decreased injection pressure, delayed injection timing, obvious engine power drop, and even sudden engine stalling in severe cases.
Fault Analysis: Excessive fuel return is mostly caused by severe wear of the needle valve assembly or poor fitting tightness between the needle valve body and the injector shell. In addition, the valve plate is a vulnerable part that is easily overlooked. Once the valve plate is worn, it will also lead to a sharp increase in fuel return volume, disrupt the normal fuel injection cycle, and ultimately damage the overall operating performance of the diesel engine.
