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What Does Common Rail Injector Failure Mean?
Baileys Diesel • July 12, 2018
In a seperate post, we discussed the most common symptoms of a failing injector , and what exactly causes each one of these symptoms. But what exactly does it mean when your Diagnosis is “common rail injector failure”? To begin with, let’s take a look at these injectors, compared to the older systems.
Looking at the situation from the outside, these newer injectors have to work at pressures that are basically double what the older systems worked at, and they are required to inject three to five times per stroke, which is of course three to five times more often. To make these pressures and number of injections possible, tolerances have been reduced, and new technologies have been employed. The fact that many of these injectors will see upwards of 150,000-200,000 kms is therefore quite impressive.
These injectors have done an awful lot of work by the time that 150,000-odd kms come around. But what exactly makes them fail? To date, BDG has blueprinted thousands of these injectors, and here are the three main common rail injector failures that we discover.
The Three Main Causes of Common Rail Injector Failure
- The injector simply stops – This is caused by a short in the injector coil. From all of the injectors that we have built, we have failed less than 50.
- High fuel consumption – The nozzle orifice is very important to the overall engine performance and economy. The sizing of these holes governs the flow rates and the level of atomisation achieved inside the cylinder. Over time, (and being subjected to pressures up to 160 bar) these holes enlarge, which generates poor atomisation and increases the fuel consumption. This wear occurs in the nozzle body, not the spindle. BDG estimates the number of injectors seeing this failure (based on component condition) to be approximately 5%.
- Cold knock – By now a well-known phenomenon in the Hilux, the car makes heavy detonation noises only when cold. By the time it is warm, you would not know that there were any issues. This failure represents around 95% of ALL injectors seen by BDG, and it is by far the main cause of failure in these injectors.
In our experience, this failure is caused by the main spindle down the centre of the injector. It starts to “pick up” in the bore, just like a seized liner and piston, only on a smaller scale. The issue is most prominent when the vehicle is cold, and the tolerances are at the minimum. Friction is at its highest, and actually holds the injector open for longer, over-fuelling the individual cylinder.
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