DVG Motoring Tip – Diesel Injectors

 In DVG Motoring Tips, DVG News

What you need to know about diesel injectors

A quick Internet search will come up with a plethora of products and methods that claim to clean dirty diesel injectors. However the reality is that unlike petrol injectors, diesel injectors aren’t that prone to developing build-ups that block their nozzles or affect fuel atomisation. In fact the symptoms that many attribute to dirty injectors – loss of power, missing on start up, poor running, increased fuel consumption and exhaust smoke are more often than not related to issues other than injector deposits.

Diesel injectors operate at very high pressures, up to 1800 bar (26,000psi) is not unusual, and this helps keep them clean, but it also means that, in time, they wear out. Depending on the type of injector and the vehicle’s use, this can mean they will need to have their nozzles replaced anywhere from around 100,000km. Certainly most injectors that have done 100,000km won’t be at their best and no amount of cleaning is going to change that.

So how do you tell the difference between a dirty injector and a worn injector? It’s quite simple really. You take them to a diesel injection specialist who will test them. If the injector fails the test the nozzles are most likely worn and need to be replaced. But if diesel specialist thinks they only need to be cleaned, and can be cleaned successfully, they’ll do it.

As unpalatable as this may sound, the bottom line is that there are no user serviceable parts in diesel injectors and pumps. If you are going to do any DIY fuel system repairs, limit it to replacing the fuel filter. Even most general repair workshops don’t get too involved in such specialised repairs. Instead, they will often send the whole vehicle to a diesel injection specialist for repair, or at most they’ll remove the fuel system parts and send them out for repair.

As for the solutions found on the Internet, you need to make your own decision as to their effectiveness – and safety.  We certainly couldn’t recommend some of the ‘home-grown’ solutions we’ve seen, and have certain reservations about most of the others as well.

Chemical cleaners may assist in cleaning a dirty fuel system, or they may just loosen build-ups resulting in on-going fuel filter blockages, or other problems, but they will not restore a worn injector or overcome a mechanical problem in the engine. If you chose to follow the cleaning route, be prepared that it may not fully resolve the issue and that a proper repair of some sort may still be needed afterwards.

Adding a quantity of petrol into the fuel tank, as suggested on a number of Internet forums, is very risky and is certainly not recommended. For one it significantly lowers the fuel’s flash point – the temperature at which it will combust. This presents a potential safety issue, particularly given that diesel is regarded as a relatively ‘safe’ fuel that can be in some types of hazardous environments. It also changes the way the fuel burns in the cylinder, which may not be good for the engine.

But it is also potentially hazardous to the fuel system components as it can affect the fuel’s lubricity. Diesel fuel system components are made to very fine tolerances and rely on the diesel fuel for lubrication, but petrol is a solvent which can strip the lubricant from the parts resulting in expensive damage. This is much more of an issue with later Common Rail diesel fuel systems (i.e. most later small diesels) that operate at very high pressures. Like chemical cleaners, this will not overcome mechanical and wear related problems, and in fact it’s questionable if it can even effectively clean an injector.

Other methods, usually found on DIY forums, purport to show step by step removal and dismantling of injectors for cleaning, or even how to replace injector nozzles. However these guides overlook a very fundamental issue – the need for specialised equipment, facilities and knowledge to determine if the injector is serviceable and to reset its opening pressure. Quite simply, the job isn’t done properly if injection pressures aren’t set – and there’s a very real risk of causing engine damage if this isn’t done properly.

Bear in mind also that injector nozzles have very fine spray holes and a well blocked nozzle may not be recoverable at all.


Click through to our Servicing page to book a time to check your injectors!


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