What are the common fault phenomena of the injector assembly of Caterpillar 336 excavator?

1.Poor fuel atomization

Poor fuel atomization is one of the common faults of the injector assembly of the CAT 336D excavator, which is manifested by the decrease of diesel engine power, emission of black smoke, and abnormal sound of the machine operation. This fault is mainly caused by the following factors:

1. **Insufficient fuel injection pressure**: The working pressure of the injector is the key to ensure sufficient fuel atomization. When the fuel injection pump is worn, the pressure regulating spring fails or the fuel filter is blocked, the fuel injection pressure will drop, which will affect the atomization effect of the fuel.

2. **The spray hole is worn and carbonized**: During long-term use, impurities and carbon deposits in the fuel will gradually clog or wear the spray hole, causing the diameter of the spray hole to become larger, and the fuel cannot form an ideal mist, but is sprayed in large droplets, reducing the combustion efficiency.

3. **The spring end face is worn or the elastic force is weakened**: The return spring inside the injector is responsible for quickly resetting the needle valve after fuel injection. If the spring end face is worn or the elastic force is weakened, the needle valve will not be closed tightly, affecting the fuel injection accuracy and atomization effect.

2. Needle valve stuck

Needle valve stuck is another common injector failure, which manifests as reduced engine power, shaking, and even failure to start in severe cases. The main causes of this failure include:

1. **Water or acidic substances in diesel**: These substances will corrode the needle valve and its mating surface, causing the needle valve to rust and get stuck.

2. **Damage to the needle valve sealing cone**: The combustible gas in the cylinder enters the mating surface to form carbon deposits, making the needle valve unable to move. In addition, the wear between the needle valve and the valve seat will also aggravate the stuck phenomenon.

3. **Fuel filter failure**: Failure to effectively filter out impurities and moisture in the fuel, resulting in contamination of the needle valve and its mating surface.

3. Nozzle dripping

Nozzle dripping means that fuel still seeps out of the spray hole when the injector is closed. This failure will cause the diesel engine to start difficultly at low temperatures, white smoke from the exhaust pipe, and turn to black smoke as the temperature rises, and increase fuel consumption. The main reasons for dripping include:

1. **Wear of the sealing cone surface of the needle valve body**: Under the impact of high-pressure fuel, the sealing cone surface of the needle valve body will gradually wear or appear spots, resulting in poor sealing.

2. **Stuck needle valve**: Due to rust, carbon deposition or wear, the needle valve cannot move flexibly, resulting in loose closure.

3. **Improper installation of the injector**: Failure to properly adjust the tightening torque of the injector or damage to the sealing gasket during installation can also cause dripping.

IV. Excessive oil return volume of CAT 336 used excavator

Excessive oil return volume means that during the injection process of the injector, part of the fuel flows back to the fuel tank through the return pipe, resulting in a decrease in injection pressure and a delay in injection time, which in turn affects the engine power. This fault is usually caused by the following factors:

1. **Severe wear of the needle valve pair**: Wear between the needle valve and the valve seat will increase the gap, making it easier for the fuel to leak under high pressure.

2. **The needle valve body and the injector housing are not tightly matched**: Due to long-term use or improper installation, the matching clearance between the needle valve body and the injector housing increases, resulting in fuel leakage.

3. **Valve plate wear**: The valve plate is a key component for controlling fuel reflux. Its wear will cause the reflux channel to increase, thus affecting the normal operation of the injector.

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