Introduction to MTU Injectors

2025-09-25
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The MTU injector is like the "precise nutritionist" of the engine, responsible for delivering fuel to the engine's combustion chamber in the most appropriate manner. It directly affects the fuel combustion efficiency; precise fuel injection allows the engine to produce more powerful output, while optimizing the amount and timing of fuel injection helps to avoid fuel waste and improve fuel economy. Good injection performance also promotes thorough fuel combustion, reducing the generation of harmful gases and aligning with environmental standards.

 

The working principle of the MTU injector:

  • Fuel high pressure generation: The common rail injection system where the MTU injector is located includes components such as a high pressure pump and a common rail pipe. The high pressure pump is a multi-cylinder radial plunger pump, driven by the diesel engine through a gear mechanism, which supplies fuel into the common rail, allowing the fuel pressure in the rail to reach about 120MPa.
  • Electronic control device regulation: The electronic control device perceives the pressure in the system through a pressure sensor mounted in front of the oil rail. Fuel enters the high-pressure pump through a throttle valve, and under the control of the electronic control device, adjusts the pressure by throttling the flow rate, allowing the common rail pressure to maintain an appropriate value according to the engine's operating conditions.
 
  • Working process of the fuel injector: Each cylinder head is equipped with a fuel injector controlled by an electromagnetic valve, which connects the common rail pipe to the injector through a high-pressure fuel line. When the electronic control unit issues a command, the electromagnetic valve of the injector opens, relieving pressure above the needle valve. Then, the fuel pressure opens the needle valve, allowing high-pressure fuel to spray into the cylinder through the nozzle. When the electromagnetic valve of the injector closes, the pressure above the needle valve is restored, and the needle valve closes under the action of fuel pressure and spring force, stopping the injection. By controlling the opening time of the electromagnetic valve and the pressure in the common rail, the injection quantity can be precisely controlled, as well as adjusting the amount of fuel at the ignition delay period.

 

How can one determine if the MTU injector needs to be replaced?

  • Assessment of Engine Operating Conditions

  1. Engine shaking: If the injector is damaged and fuel injection is obstructed, the engine will exhibit symptoms of operation shaking during operation.
  2. Power loss and increased fuel consumption: Injector failure can lead to an inability to ensure the injection quantity and pressure, resulting in reduced vehicle power and increased fuel consumption.
  3. Exhaust emissions are abnormal: A malfunction in the engine injectors can affect the mixing and combustion of the combustible mixture, leading to an increase in exhaust emission pollutants. This may result in the appearance of black smoke, white smoke, and may also be accompanied by backfiring.
  4. Difficulty starting and even stalling: When the fuel injector is severely damaged, the vehicle may experience difficulty starting and could even stall suddenly while driving.
 
  • Listen to the working sound with a stethoscope: When the engine is running or starting, use a stethoscope to check the working sound of the fuel injector. Normally, the injector produces a regular 'click' sound, and the sound frequency changes with the engine speed. If no sound is heard or the sound is abnormal, there may be a problem with the injector.
  • Resistance measurement: Turn off the ignition switch and disconnect the injector connector. Use a multimeter to measure the resistance across the injector terminals. The standard resistance values for injectors vary by model; generally, low-resistance injectors should have a resistance of 2 to 3 ohms, while high-resistance injectors range from 13 to 16 ohms. If the resistance value deviates from the standard, the injector needs to be replaced.
  • Dedicated equipment testing: Remove the injector and install it on the injector testing bench for inspection. If the injection pressure does not meet the corresponding technical standards, the atomization of the injector is poor, there is dripping or leakage, and it cannot be restored after cleaning and adjustment, then the injector must be replaced.
 
  • Cylinder cut-off method for diagnosis: After starting the engine, maintain a stable speed and gradually loosen the high-pressure fuel pipes, observing the changes in engine speed. If the engine speed decreases significantly after cutting off a cylinder, it indicates that the injector for that cylinder is normal; if the speed decrease is not significant and the engine's white smoke or black smoke decreases, it indicates that the injector for that cylinder may be damaged.
  • Appearance and carbon deposit inspection: Remove the injector. If a large amount of wet carbon deposits is found on the injector nozzle, it indicates that the injector is not functioning properly. Also, check for any damage, corrosion, or wear on the injector's appearance, whether the seal gasket is intact, and if the mounting seat is clean, as any issues may also affect the performance of the injector.