Why Change Diesel Injectors?

150 150 Brooke Hamilton

Is It Time to Change my Diesel Injectors?:

Its a common question; why change diesel injectors and how to tell when mine are worn?

So we got about answering it:

Difference in Work Load:

One of the most surprising things about common rail injectors is the work load that they are subjected to.  The older injection systems operate around 1000 bar and inject once per combustion event. Modern Diesel Injection systems inject up to 5 times per combustion stroke and with anything up to 2200 bar!

Tolerances in these injectors:

The main way these injectors are able to deal with such massive work loads by they employing SUPER FINE Tolerances in order to promote best possible performance.

A great indication of these tolerances was shown in our blog post ‘BDG’s Party Trick’ which you can see by clicking here.

The Bits that fail inside the injector:

Unlike many years ago where a nozzle would simply wear out, metallurgical advancements have moved to such a point where the nozzles are now not really the issue. Whilst they do ‘wear’, its nothing like it used to be despite the much higher work loads.

So what does fail?

The most common failures we see here are Control piston and nozzle needle failures. These are the moving parts that dictate when and how the injector opens and starts injecting. The wear that we see is nearly always seizure related failures which can be due to excessive clearances (ie it worn out). However, its usually accelerated by either a lack of lubrication or physical particles coming through the fuel.

So lets take a look

Lack of Lubrication:

diesel injector lacking in lubrication

a common reason why change diesel injectors; Lack of lubrication

BDG recommends the use of BP ultimate fuel. Its not just something we say but actually something we do as all our company vehicles have a BP fuel card. We suggest this as BP Ultimate is the only fuel guaranteed to meet Euro grade diesel standards including Cetane rating, lubricity and so on.

Another potential cause of the lack of lubrication can also be water getting through the trap and into the fuel system. Water has no lubrication and under extreme injection pressures does some pretty crazy things. This leads to a highly likely scenario where scoring occurs in moving parts inside the injector. Like a seized liner and piston, once it starts its only going to spread.

The water in the fuel also causes something else which I feel is the bigger issue – RUST.

rust in common rail injector

Rust found inside common rail injectors

Physical particles in the fuel:

This is probably the bigger concern for common rail injection systems.

I actually believe there to be 2 main contributing factors, Rust and ‘Rubbish in the fuel’.

The rust can develop in the fuel rail or certain parts of the injector. After a while it will continue to grow and start to break off sections, which being after all of the filters, will go straight through the fuel system.

Click this link here to see our Blog on what we feel is the best line of defence you can give against the above two.

So How can you tell?

Why change diesel injectors? You’d want to see one of these issues:

  • Engine ‘Rattles and knocks’
    • One of the easiest tells is when the engine starts to rattle and knock. Whilst some engines are ‘naturally noisy’, its pretty clear to tell when one cylinder doesn’t match the rest.
    • These noises come from a cylinder to cylinder imbalance (or shot to shot imbalance) which highlight the injector is no longer functioning correctly.
    • *there are other potential reasons for engine noises, such as SCVs (click here for more information), engine issues, sensor issues and so on. Always best to get a GOOD Diesel mechanic to investigate.
  • Engine ‘vibration’:
    • Clients usually comment after having their injectors replaced ‘The engine is so smooth now”.  This is usually due to variations in shot to shot consistency. The ECU can’t learn and therefore cannot ‘cover up’ these issues
  • Smoke:
    • Another great indication that something isn’t quite right is the presence of smoke from the exhaust. Smoke caused from diesel injectors is usually due to incorrect flow rates. Smoke is usually caused from wear or control issues with the injectors.
    • *Diesel Smoke can be caused by MANY other factors that can cause smoke in diesel engines.
  • Fuel Economy:
    • This isn’t always the best indication as sometimes as nozzles wear and flow more, it can actually give better fuel economy!
  • Injector Feedback Values:

So; Why Change Diesel Injectors?

Why change Diesel Injectors? There’s really only 2 reasons:

  1. To Fix a problem
  2. Replace the injectors with a more ‘robust’ injector.
    1. To learn more, Click here



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