Injectors
A common rail injector is the most heavily loaded component in your entire engine. It opens and closes up to 2,000 times a minute at a pressure of 1,800 to 2,500 bar.
For comparison, that is the weight of a car resting on an area the size of a fingernail — two thousand times a minute, every time you drive. And as if that were not enough: the only thing lubricating the injector is the diesel it sprays out itself.
The needle seals metal against metal. There is no gasket inside an injector. The needle closes directly onto its seat at full pressure, and after hundreds of millions of openings the seat wears or picks up deposits. Then the injector starts to drip after it should have closed.
Diesel has lost lubricity. Modern low-sulphur diesel lubricates less well than the fuel these engines were originally designed for. Water and contamination in the fuel cause cavitation that erodes the material from the inside.
The spray holes coke up. The holes in the nozzle tip are 0.10 to 0.15 millimetres — thinner than a hair. Even a very thin layer of deposits changes how the fuel is distributed in the combustion chamber.
The outlet orifice wears. This is the small channel that controls how quickly the needle lifts. As it wears, injection timing drifts — and the engine starts to knock, especially when cold.
The piezo crystals lose stroke. In piezo injectors the crystals contract with age and heat. The injector opens slightly too little, or slightly too late.
The deterioration is gradual and invisible. The vehicle does not lose power overnight. It just runs a little harsher, smokes a little more and drinks a little extra — over tens of thousands of kilometres.
Most people only notice when a fault code appears, or when the engine starts idling roughly. By then the injectors have usually been on their way out for a long time.
And that is the good news. An injector that has covered 250,000 kilometres is not destroyed — it is worn. The needle, the seat, the seals and the valve can be replaced, and the body can be reused. That is also why reconditioning typically costs about half the price of a new original injector.
But first it has to be measured. Five different faults produce almost the same symptom in the vehicle. Only a test on a proper test bench can tell them apart — and tell you whether the injectors are the problem at all.
