Modern Diesel engines are operation at incredibly fine tolerances in order to achieve low tailpipe emissions injector are operation at ever increasing pressures and with small multi nozzle configurations to atomise the fuel. As manufactures keep increasing service intervals including the mileage to change the diesel filter we are seeing more issues with restricted filters and in some cases damaged components .
A modern diesel vehicle fuel filter can filter down to three micron ( one micron is .0001mm ) if dirt enters the system and pass through the filter then expensive damage will almost certainly occur.
This is a recent case study on a non start Audi Q2 presented to our workshop after having a secondhand engine fitted the story was that the original engine had suffered a catastrophic piston failure and a secondhand low mileage engine was sourced . Initially the vehicle started and ran but after a few minuets cut out and would crank but not fire.
Our assessment revealed multiple fault codes throughout the vehicle most of which had been introduced after saving and then clearing these we had no returning faults even though we had a crank non start situation . We then progressed onto checking live data confirming cranking rail pressure and then injector triggering using Pico scope with a current clamp followed by a relative compression test . Once carried out that everything was in place for this vehicle to be able to run and the conclusion was that the injectors were not injecting any diesel .
With customer approval we investigated the condition of the diesel and the contents of the fuel filter which had been changed prior to us receiving the vehicle . The filter was covered in a metallic coating and the filter housing and contents were showing sever contamination.
To see how far the contamination had gone we removed the metering valve from the high pressure pump and this was also full of metal particles and contamination.
This high level of metal and contamination would obviously quickly block the injectors and result in the non start situation . The only unknown in this situation is whether the contamination was already in the vehicle or introduced via the donor engine . The likely answer is that this was introduced from the donor engine but has now travelled around the injection system resulting in a very expensive repair as it will require fuel tank forward component removal and anything that cannot be taken apart or fully flushed will require replacing this is why we would never recommend using any secondhand parts on an injection system Diesel or Petrol .
