Diesel Common Rail Issues

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Updated: January 2, 2020

The key to diagnosing a fault is having an understanding of how the system operates.

Cooma Diesel and Turbo in Canberra provide technical advice and regular training courses to automotive technicians on diagnosis and repair as well as supplying new and remanufactured fuel injection parts and turbo chargers. Their affiliated company Specialist Tools Australia stocks the specialised tools to ensure accurate diagnosis and fast repair.

Achieving a satisfactory and cost effective end result, it is critical to obtain a good diagnosis and identification of any faults before purchasing any parts or proceeding with repairs. This is true of almost anything not just motor vehicles.

In the case of current diesel fuel system issues eg. Common Rail (C/R) and other electronic operated systems, technicians tend to over complicate the issues.

We should think of and diagnose these engines initially as we would conventional mechanical diesel fuel systems.

The Common rail fuel system utilises a high pressure supply pump to create fuel pressures of up to 200 MPA (200,000KPA), which is supplied to a common manifold (rail) to be utilised by the electronically operated injectors as the ECU (Engine electronic control unit) designates. Using many sensor inputs from altitude, temperatures, load demand, boost pressure, the resulting charge injected into the cylinders is extremely well atomised, timing is accurate, and fuel is burnt precisely, reducing exhaust emissions, increasing efficiency and performance.

In addition, the engine’s electronic control unit can control multiple injections (4-9 times per piston stroke), some before and after the main injection. These are “pilot” and “post” injections which are utilised to help reduce noise, help cold starting, reduce exhaust emissions and improve overall performance.

When beginning diagnosis of the C/R systems a check of DTC (fault codes) would be first as this will show us if the fault is with a component with reference and feedback capability.

One of the most common faults with C/R systems can be traced to damage by water contamination in fuel. This 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).

Check injector compensations (feedback) levels, injector return volumes (magnet valve injectors) or return pressures (Piezo injectors).

One of the most common faults with C/R systems can be traced to damage by water contamination in fuel. This 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).

Check injector compensations(feedback) levels, injector return volumes (magnet valve injectors) or return pressures (Piezo injectors).

Check function of EGR valve. Note: the valve can often be temporarily blocked off as a test.

We can learn a lot from a basic visual inspection of a Diesel sample. We are looking for evidence of a contamination event which has occurred.

Obtain a fuel sample from an area where water and particles would be more likely to gather, for example the fuel filter base or fuel tank pick up canister.

Place the fuel sample into a clear glass bottle about 100ml x 25-30mm diameter. Sample bottles can be purchased from Specialist Tools Australia. Water may be seen within the sample, or tested for with a test strip or paste Inspect the sample using a small high energy LED torch, the light will make the metal particles appear larger and become visible to the naked eye.

Darker red/orange particles may indicate rust from a rusty fuel tank in earlier vehicles or aftermarket steel fuel tank fitted where a poly tank was original or this rust could simply have been pumped in during a routine fill.

Rust is a very serious threat, it can be in the form of sub-micron particles which easily travel through the fuel filter and once inside the fuel system it will continue to cause an increasing amount of abrasive rust to form.

The bright shiny metal is from wear to components such as injector spindle or push rod, supply primary trochoid pump gear set and cam block. The amount of this metal will indicate the amount of wear that has taken place up to now. In a 100ml bottle this will vary from 20-100 particles to many thousands, at this point we can gather particles that can’t be seen even with the LED light by using a small super strong Neodymium Rare Earth magnet held against the side of the test bottle, particles will quickly gather at the area around the end of the magnet providing the repairer with proof for their diagnosis.

Check out the training video on injector leak off at youtu.be/zPNnn0uX-68 Tools & advice from Specialist Tools Australia – www.waterindiesel.com.au/specialist-tools-australia
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