Why Do Diesel Injectors Fail? Key Causes and Repair Tips

Diesel injectors are one of the most vulnerable parts of a diesel engine. Operating under high temperature and pressure conditions for extended periods, they are prone to failure. This blog analyzes the causes of common diesel injector failures and provides methods for prevention and troubleshooting.

Functions of Diesel Injectors

Diesel injectors are critical components of the fuel system, with three main functions:

  1. Atomizing high-pressure fuel into a fine mist.
  2. Creating a spray pattern with appropriate angles and penetration to form a quality combustible mixture with fresh air in the combustion chamber.
  3. Delivering fuel in accordance with a specified timing, ensuring accurate start and stop of injection without leakage.

The diesel injectors are generally classified into two types: open and closed. Closed diesel injectors are widely used in diesel engines. The precision fit of the nozzle needle and nozzle body in injectors makes them highly susceptible to faults under extreme working conditions. Some injectors fail within months or even days, making it crucial for users to understand the causes of these issues and take preventive measures.

1. Nozzle Needle Seizing

When the nozzle needle seizes, the injector fails to operate, causing single-cylinder to stop working.

Causes

  1. Poor Heat Dissipation:
    • High temperatures in the combustion chamber (up to 2000°C) require the nozzle to dissipate heat effectively. Inadequate heat dissipation may lead to overheating and seizing of the nozzle needle.
    • Common causes of poor heat dissipation include improper installation of copper washers (e.g., dirty washers or the use of substitutes like asbestos rope or old cylinder gaskets), incorrect fuel timing leading to prolonged post-combustion, or damaged sealing surfaces allowing combustible gases to create carbon deposits.
  2. Fuel Contamination or Corrosion:
    • Dirty diesel, water, or acidic substances can corrode the nozzle needle.
    • Prolonged storage, exposure to moisture, or outdoor storage may lead to rusting.
  3. Improper Handling or Maintenance:
    • Nozzle needle may seize due to physical damage, improper cleaning, or incorrect assembly during maintenance.
  4. Residue from Rust-Preventive Oil:
    • Failure to remove protective oils from new injectors may cause the needle to stick when heated.

Preventive Measures

  • Use certified nozzles and properly fitted copper washers. Avoid substitutes like asbestos rope or old gaskets.
  • Ensure fuel timing, valve timing, and injection pressure meet technical specifications.
  • When assembling or disassembling the injector nozzle, avoid touching the nozzle needle, and do not mix parts. Ensure the injector mounting hole is clean before installation. Do not use too many copper washers, as this can alter the spray distance, leading to incomplete combustion, overheating, carbon buildup, and sticking. Avoid using materials like asbestos rope as a substitute for copper washers, as this can affect heat dissipation. Tighten the injector nozzle bolts evenly in 3–4 steps, ensuring the torque meets the specified requirements.
  • Store injectors removed from engines in clean oil and plug the installation holes with wooden plugs during long-term storage.
  • Boil new nozzles in clean diesel at 60–80°C for 10 minutes to remove rust-preventive oil before installation.

2. Carbon Deposits Blocking Nozzles

Symptoms

When the injector nozzle holes are partially blocked by carbon deposits, the fuel injection decreases, return flow increases, and the diesel engine loses power. If the nozzle holes are fully blocked by carbon, the engine will show the same issues as a stuck nozzle needle: the injector stops injecting fuel and fails to work.

Causes

The main reason for carbon buildup blocking the injector nozzle is that diesel and engine oil do not burn completely in the cylinder. This mixes with dust from the unfiltered intake air to form carbon deposits. These carbon deposits stick to parts like valves, pistons, cylinder liners, exhaust pipes, and injector nozzles inside the combustion chamber.

Preventive Measures

  • Ensure fresh air is sufficient in the diesel engine cylinder and exhaust gases are fully removed.
  • Keep the injector nozzle in good condition. Injection pressure should meet the required range, with proper atomization, no dripping, and no leaking.
  • Keep the engine in good condition to prevent oil burning.
  • Avoid excessive use of the throttle during startup and do not force multiple starts to prevent unburned fuel accumulation, which can cause carbon buildup and startup difficulties.

3. Increased Nozzle Needle Lift

Symptoms

When the injector nozzle needle lift increases, engine power decreases, and fuel consumption goes up. In some cases, the exhaust may produce smoke. Disassembling the injector reveals dents on the sealing surface of the injector body caused by the impact of the nozzle needle shoulder.

Causes

Repeated operation over time causes wear on the injector body’s sealing surface and the nozzle needle shoulder, leading to increased needle lift.

Solutions

  1. Use chromium oxide or aluminum oxide to regrind the injector body’s sealing surface on a glass plate until it is flat and leak-free.
  2. Replace the injector body if necessary.

4. Air in High-Pressure Fuel Lines

Symptoms

When the diesel engine is running, one cylinder may not work properly, and the sound it makes will also be abnormal. Using the “cylinder cut-off method” to diagnose, if you loosen the high-pressure fuel pipe of that cylinder, you will notice gas escaping from the pipe.

Causes

  1. The contact surface between the upper end of the nozzle needle seat and the injector is uneven, allowing gas to pass through the gap at the joint into the injector body and then into the high-pressure fuel pipe.
  2. The injector nozzle needle gets stuck in the open position, so during the compression stroke of the diesel engine’s working cycle, high-pressure gas enters the high-pressure fuel pipe through the injector nozzle holes.

Solutions

  1. Use chromium oxide or aluminum oxide to polish the end surface of the injector nozzle needle seat on a glass plate. Hold the needle body by hand, invert it onto the glass plate, and polish until the surface is smooth.
  2. Disassemble the needle using the method for removing a stuck needle. Apply a small amount of clean engine oil to the needle and place it inside the nozzle body for polishing.

Final Thoughts

Diesel injector failures can be costly, but with proper care and timely maintenance, you can extend their lifespan and improve engine performance. By addressing common causes like heat dissipation, contamination, and wear, you’ll reduce downtime and save on repairs. Regular inspections and following preventive tips will ensure your diesel engine runs smoothly for years to come.

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Toni Tao

Hi, I’m Toni Tao, a manager at ERIKC Diesel. I have more than 10 years of experience and focus on providing quality diesel parts and great service to customers worldwide.

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