Fuel injector return volume measurement

Due to its operating principle, the return volume of the Common Rail injectors consists not only of the leaked oil volume. The greater part of the injector return consists of the control oil volume of the injectors. The control oil volume is approximately the same as the volume injected into the combustion chamber.

Wear or a defect in the injector can lead to an increase in the return volume. The higher the return volume the more the high-pressure pump has to pump into the rail to maintain the pressure. If the return volume exceeds certain limit values, the high-pressure pump can no longer adequately fill the rail and the pressure collapses. This can lead to the following effects:

• Engine jolts, misfires
  
• Engine shuts down
  
• Engine does not start, especially if the engine is hot and there is not much fuel in the fuel tank
  

This test module can be used in conjunction with the return volume measuring device to measure the injector return volumes.

Connection of the measuring equipment

The return volume measuring device must be connected as follows:

• MFK1: Measurement of the fuel return temperature
  
• MFK2: Measurement of the fuel return volume
  
• The hydraulic line ”IN” must be connected to the return line of the injector to be measured. The ”OUT” line must be connected to the corresponding connection of the return line.
  
• The electrical connector located on the hydraulic line ”IN” must be connected to the corresponding socket at the measuring equipment.
  
• The positive and negative connections must be connected to the vehicle electrical system.
  

Notes on using the measuring equipment

• The measuring equipment must never be operated without connection to the vehicle network!
  
• The fan openings on the back must not be closed!
  
• The measuring equipment must be set up in such a way that as much cool air as possible can be drawn in!
  

Test preconditions

• Engine at operating temperature (only if engine still starts; measurement at starting engine speed can also be carried out with the engine cold).
  
• Fuel level sufficiently full (reserve fuel lamp must not light)
  
• No fault in fuel supply system
  
• No external leaks in common rail system
  
• No fault code stored for rail pressure sensor, volumetric flow regulating valve or rail pressure control valve
  

Principle of the measurement

A flow sensor is integrated in the return volume measuring device; this works with a ring piston according to the volumetric principle. The sensor can measure volume flows of 10 to 500 cm³/min.

To supply the sensor with fuel with a lower and more even temperature, a cooler and electric fan are integrated. The fan openings must not be blocked!

The fuel return temperature is an important general condition for the measurement (only with the engine running). This is why a temperature measuring point is fitted at the input of the measuring equipment; this is evaluated via the tester.

Sequence of the measurement

Measurement with the engine running:

The measurement runs at an engine speed of 2000 rpm; the engine speed is raised automatically. Prior to the return volume measurement, the rail pressure is raised to 1600 bar. Here, it is determined whether the system still reaches the maximum rail pressure. If the 1600 bar is not reached, the highest rail pressure reached in this test is stored and used as a second test point for the return volume measurement.

Subsequently, the following measurements are made at 2000 rpm:

• Return volumes at 300 bar
  
• Return volumes at 1600 bar (or at the maximum rail pressure achieved)
  

Measurement at starting engine speed:

If the engine no longer starts, the measurement can also be carried out at starting engine speed. No specific engine temperature is necessary for this.

General information

Sales / distribution of the measuring equipment:

Currently, the measuring equipment is planned for use and has been delivered in the following countries:

• Germany
  
• France
  
• Italy
  
• Spain
  
• Great Britain
  
• Belgium
  

Diagnosis report:

After the return volume measurement has been carried out in cases of warranty, the diagnosis report must be enclosed with the parts for parts subject to return obligation. For parts not subject to return obligation, the diagnosis report must be placed in the vehicle folder.