Common Rail High-Pressure Testers

Frequently Asked Questions About Common-Rail High-Pressure Testers

Common-rail high-pressure testers enable independent testing of fuel pressure in the high-pressure section of a common-rail diesel system. They assist in diagnosing startup problems, insufficient rail pressure, and faults in the high-pressure pump, pressure regulator, or rail pressure sensor.

• What is a common-rail high-pressure tester?

  A common-rail high-pressure tester is a measuring device specifically designed for very high fuel pressures.
  
  It is used to determine the actual pressure in the high-pressure circuit of a common-rail diesel system or to check the operation of the rail pressure system.
  
  Depending on the tester, the measurement is performed mechanically via a suitable high-pressure line or electrically via the connection or signal from the rail pressure sensor.

• What is the rail pressure in a common-rail system?

  Rail pressure is the fuel pressure in the common high-pressure reservoir—known as the rail.
  
  The high-pressure pump compresses the fuel and delivers it to the rail. From there, the fuel is supplied to the individual injectors via high-pressure lines.
  
  The required rail pressure varies depending on the engine, operating conditions, and system configuration.

• Why is the common-rail high-pressure measured?

  A high-pressure measurement is particularly useful when checking whether the fuel system is actually building up the rail pressure required by the vehicle manufacturer.

  Typical reasons for diagnosis include, for example:

  • Engine won’t start
  • Long start-up time
  • Insufficient rail pressure
  • Loss of power
  • Fuel pressure error codes
  • Suspected faulty high-pressure pump
  • Inplausible rail pressure sensor signal
  • Pressure deviations at different engine speeds

  The measurement should always be evaluated in conjunction with additional diagnostic information and manufacturer specifications.

• How much rail pressure does a common-rail diesel engine require?

  There is no universally applicable rail pressure for all common-rail systems.
  
  The required pressure depends, among other things, on the injection system used, the engine, operating conditions, load, and manufacturer.
  
  Modern common-rail systems can operate at pressures well over 2,000 bar. Therefore, a high-pressure tester must have a measurement and operating range suitable for the vehicle in question.
  
  The specific target values must be obtained from the vehicle manufacturer’s repair and diagnostic information.

• What is the difference between start pressure and rail pressure during motor operation?

  When starting the engine, sufficient pressure must first be built up in the rail so that the control module can enable or correctly execute the fuel injection.
  
  During engine operation, the engine management system adjusts the rail pressure based on engine speed, load, and injection strategy.
  
  Therefore, it may be diagnostically useful to check the pressure both during the starting process and under various operating conditions.

• What does it mean if sufficient rail pressure isn't built up during startup?

  Low rail pressure can have various causes.

  Possible sources of error include, for example:

  • insufficient fuel supply in the low-pressure system
  • air in the fuel system
  • clogged fuel filter
  • faulty feed pump
  • worn high-pressure pump
  • faulty pressure regulation
  • leaking or internally leaking injectors
  • excessive injector return flow
  • faulty pressure relief valve
  • faulty sensors

  Therefore, the high-pressure test should not be considered in isolation. Additional low-pressure and return flow tests are often required.

• What is the difference between analog and digital common-rail high-pressure measurement?

  An analog high-pressure tester displays the fuel pressure via a mechanical high-pressure gauge.

  Digital high-pressure testers display the measured value electronically and may offer additional functions depending on the model.

  However, the type of display alone is not the decisive factor for the actual diagnosis. The most important factors are:

  • appropriate measurement range
  • sufficient pressure resistance
  • measurement accuracy
  • compatible connections and adapters
  • safe high-pressure lines
  • suitability for the system being tested

  Autotestgeräte Leitenberger offers both analog and digital solutions for various pressure ranges.

• Why should the actual rail voltage be checked in addition to the diagnostic value?

  The rail pressure displayed by a diagnostic system is based on the signal from the rail pressure sensor.
  
  If the sensor itself, its power supply, wiring, or signal processing is faulty, the displayed value may differ from the actual system pressure.
  
  An independent test can therefore help determine whether there is actually a pressure problem in the hydraulic system or possibly an issue with the sensor system or signal transmission.
  
  Which comparative measurement is possible and permissible depends on the vehicle and the test equipment.

• Can a common-rail high-pressure tester be used while the engine is running?

  Depending on the model, suitable test equipment may be designed for static and dynamic measurements.
  
  This allows, for example, the pressure to be monitored during the startup process or at varying engine speeds.
  
  However, particularly strict safety requirements apply here. The test equipment, all hoses, and adapters must be suitable for the pressure that will be generated and connected in accordance with the operating instructions.

• What should you keep in mind when connecting a common-rail high-pressure tester?

  Common-rail systems operate at extremely high pressures. Therefore, only high-pressure lines, adapters, and measuring devices specifically designed for this purpose may be used.
  
  Before connecting the system, it must be prepared in accordance with the vehicle manufacturer’s specifications and, if necessary, depressurized.
  
  Damaged, kinked, or unsuitable high-pressure hoses must not be used.
  
  During testing, no body parts should be in the vicinity of potential high-pressure leaks.

• What measurement range should a common-rail high-pressure tester have?

  The measurement range must be compatible with the maximum pressure that can occur in the system under test.
  
  Leitenberger currently offers common-rail high-pressure testers with various measurement ranges, including models rated up to 1,000, 1,600, and 2,500 bar.
  
  For modern systems with particularly high injection pressures, a tester with a sufficiently high permissible operating and measurement range is required.
  
  The technical specifications of the vehicle and the tester used are crucial.