Smart Solutions

Diagnostic Tools To Rectify Common Rail Fuel System Faults

Most modern Diesel fuel system faults become obvious due to the vehicles poor performance in many ways.

It is important to realise that Turbo, DPF and other faults may display as primary but are often due to fuel system issues.

One of the most common faults with Common Rail Diesel systems  can be traced to damage by water contamination in fuel.

With flooding and higher than usual rainfall throughout much of Australia and especially the Eastern States over the last 12 months, coupled with diesel fuels being hydroscopic (readily drawing water from the atmosphere and retaining it), many diesel storage tanks and even vehicles have inadvertently become contaminated with water.

From left- Common rail diesel injector fuel return flow test kit SA-8392 and Injector return pressure measurement tool designed for testing Piezo injectors SA-2897K.

From our experience, the most important initial test you can carry out is to obtain a fuel sample. We can learn a lot from a visual inspection of a fuel sample.

Fuel samples should be obtained from an area where water and particles would be likely to gather, for example from the fuel filter base or the fuel tank pick up canister.

Place it in a small clear bottle and then inspected with an LED light.

We are looking for contamination damage. This process has been explained in some of our previous articles.

Once you have checked the fuel sample, there are some other tests and operational checks that can be performed to identify the components that requiring further attention: injector compensations (feedback) levels, injector return volumes (magnet valve injectors) or return pressures (Piezo injectors), injector operation isolation, function of EGR valve and operation of turbo VNT/VGT system (note: the EGR valve can often be temporarily blocked off as a test).

Contaminated fuel sample and other Fuel samples from fuel filter.

The result of fuel contamination damage can be seen with live data checks of rail pressure targets (desired) and actual pressure graphing (the readings should be within 20-40MPA of each other) and the graph will highlight rail pressure stability or instability when the accelerator pedal is operated repeatedly.

Diesel engine compression tests are a very important primary test to investigating issues in a diesel vehicle. If a vehicle

is underperforming or experiencing a combination of issues, it is worth considering a diesel engine compression test.

This test is often used when these issues are occurring:
  • Starting problems unrelated to weather or outdoor temperature
  • Poor fuel economy or increased oil consumption
  • Smoke when started till warm up
  • Uneven and rough running at start up
  • Unexplainable loss of power

The tool that we use in these situations is the Comprehensive Diesel Compression Test Kit SA-7191D as it has Japanese and European Compression Test Adaptors.

Generally, each cylinder should have 300 to 500 PSI, and all cylinders in a single engine should measure within 10 percent of each other. If the compression in the engine is too low or deviates too drastically from one cylinder to the next, this indicates internal damage to your engine.

Often common rail diesel engine faults can be traced to fuel feed pressure or volume issues, but electronic on-board diagnosis cannot always pinpoint fuel feed problems accurately, giving confusing turbo pressure or high fuel pressure circuit related fault codes.

In situations that present like this you might use the Diesel Engine Low Pressure Fuel Diagnostic Kit SA-7845 which has been designed to allow quick and easy diagnostic pressure tests to be carried out on the low-pressure fuel side of a common rail diesel system with the engine running or “Key On” test.

The kit can connect into any low-pressure fuel system that uses 9.89mm quick connectors. It measures low pressure feed from the fuel (lift) pump to the high- pressure pump and measures fuel return pressure where necessary which helps to diagnose poor/non-starting, loss of engine power, fuel filter blockages, pipe damage, connection leaks and seal damage (air leaks) and, it can be used with the engine running to establish pre/vacuum and post filter pressure variation.

To test injectors, the type of injector will need to be confirmed. This will be either Electromagnet injectors which

can be tested with Fuel Return Flow Kit Injector Test Common Rail Diesel SA-8392 or Piezo Electric Injectors which are be tested using an Injector Return Pressure Measurement Tool designed for testing Piezo Injectors SA-2897K.

Fuel contamination is the main cause of premature failure of diesel injectors.

Fitting new injectors when the fuel system is still contaminated will result in damage to the new injectors.

The fuel system must be thoroughly cleaned and components that may be contaminated must be replaced.

Fuel Return Flow Kit Injector Test Common Rail Diesel SA-8392 to test electromagnet injectors.

A common reason for pressure loss is excessive fuel being returned to the fuel tank. If the injector(s) suffer from excessive back leakage, the fuel pump cannot generate enough pressure to let the system operate correctly.

This can be more obvious at start and idle as fuel pressure (at these low engine speeds) is directly related to engine cranking speed.

A blocked or malfunctioning injector will send more fuel back to the tank, while a worn injector may be injecting too much fuel into the combustion chamber, and thus sending less fuel back to the tank.

The SA-8392 kit makes both conditions obvious. It is comprehensive and can cater for up to 10 injectors in one test. 40 adaptors are included for Bosch, Siemens, Denso and Delphi CRD systems.

Remember fault codes provide a valuable guide but may not identify the real problem!

Comprehensive Diesel Compression Test Kit SA-7191D and Diesel Engine Low Pressure Fuel Diagnostic Kit SA-7845 – for easy diagnostic pressure tests.
Issues which can initiate various broadly related fault code results are:
  • EGR system failures
  • Fuel system contamination/damaged –injectors, fuel pump etc
  • Incorrect or contaminated fuel
  • Turbo charger failures
  • Mass Air Sensor – faulty
  • Intercooler Damage – split intake intercooler pipes
  • Intake air, pressure and temperature sensor failures
  • Faulty DPF temperature pressure sensors or pressure differential switch/sensors

A visual check and physical examination components of the fuel system can be invaluable. Look beyond the fault code to related components that may give rise to any fault codes.

Specialist Tools Australia stocks many different types of diagnostic tool kits – so contact their team if you are looking for something special.

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