How to Judge If the Fuel Injector is Malfunctioning

The Importance of Fuel Injector

The fuel injector is a critical component of a diesel engine, and its performance directly impacts the engine's power output, fuel efficiency, emissions, and reliability.

According to the requirements for mixture formation and combustion, the injector should possess a certain injection pressure, injection stroke, and appropriate injection cone angle. Additionally, the injector should be able to quickly cut off the fuel supply when fuel injection needs to be stopped, without any dripping occurring.

How to Judge the Faulty of a Fuel Injector

The main faults of fuel injectors include clogging, poor atomization, fuel leaking, and excessive oil return, the symptoms of these conditions are judged by the following ways.

1. Poor Atomization of The Fuel Injector

Symptoms: The power drops in diesel engine, exhaust emits black smoke, and the machine is making unusual noises.

Fault Analysis: When the fuel injection pressure is too low, nozzle holes are worn and with carbon deposits, the spring end surface wears out or loses elasticity, these reasons will cause the injector to turn on prematurely or close late, then resulting in poor fuel atomization.

Additionally,whendiesel fuel droplets with excessively large particle sizes cannot burn completely. It flows down the cylinder wall into the oil sump, raising the oil level, reducing viscosity, and worsening lubrication. This may also lead to bearing seizure and cylinder damage.

2. Needle Valve Stuck

Symptoms: Engine power decreases, accompanied by vibration, and in severe cases, it may fail to start.

Fault Analysis: Moisture or acidic substances in diesel fuel can cause the needle valve to rust and become stuck. When the needle valve's sealing cone surface is damaged, combustible gases from the cylinder may also enter the mating surface, forming carbon deposits that cause the needle valve to seize. This renders the injector unable to spray fuel, resulting in the cylinder ceasing operation.

3. Fuel Injector is Leaking Oil

Symptoms: When the diesel engine is cold, it is difficult to start, and white smoke is emitted from the exhaust pipe. As the engine warms up, the smoke turns black, and fuel consumption is high.

Fault Analysis: When the injector is operating, the sealing cone surface of the needle valve body is subjected to frequent, forceful impacts from the needle valve. Combined with the continuous high-pressure fuel spray emanating from this point, the cone surface gradually develops wear or pitting, leading to injector dripping.

Solution: Check whether the needle valve moves smoothly. The tapered surface should be undamaged and maintain proper sealing. If not, replace the injector assembly with a new one.

4. Excessive Oil Return

Symptoms: Excessive return oil flow will cause injection pressure reduced, injection timing delayed, engine power decreased, and may even cause the diesel engine to stall.

Fault Analysis: When the needle valve assembly is severely worn or the fit between the needle valve body and the injector housing is insufficiently tight, the return fuel flow of the injector increases significantly. Additionally, the condition of valve plate is also needed to be noted, once it’s worn out, it can also cause excessive fuel return from the injector, affecting engine performance.

Conclusion

The common rail system is a high-pressure system. Do not disassemble it without authorization to avoid injury. Fuel injectors are precision components. Have them serviced at a professional repair facility and use specialized tools for disassembly.