Burgos - Spain

5 main causes of failed or blocked particulate filters

In the wake of the recent VW diesel #emissionsgate scandal, diesel vehicles are in the spotlight for all the wrong reasons.

There is no doubt that diesel cars consume less fuel, help us save money at the pump and offer comparatively more torque than their petrol counterparts.

What many people do not consider, however, is the dreaded diesel particulate filter (DPF).

DPFs are ceramic and fine-mesh devices that purify exhaust gases by removing unpleasant particles and soot.

They are a crucial part of any modern diesel engine, but can quickly negate any benefits associated with diesel car ownership.

We have published several articles on the functioning and cleaning of DPF filtersBut we have paid too little attention to the main causes of diesel particulate filter problems.

Therefore, here are our top 5 causes of DPF problems.

Failures and blockages in diesel particulate filters

1 Defective EGR valve

The EGR valves (exhaust gas recirculation) are designed for the purpose of reducing unfavourable emissions by redirecting unused exhaust gases from a diesel engine. 

They are essential for reducing nitrous oxide (NOx) emissions; however, when operated incorrectly, they can cause a number of problems.

The EGR valves decrease the level of oxygen available in the cylinder, which in turn increases the generation of diesel particulate matter (fuel that has only been partially burned). 

If an EGR valve fails, it will increase the amount of particulate matter produced by the engine, causing it to the diesel particulate filter (DPF) becomes clogged faster than usual.

2 Use of the wrong oil

The vast majority of car manufacturers set a low ash oil requirement for their vehicles.

Low ash oils are specially formulated to contain a reduced amount of sulphated ash, a by-product of diesel combustion that can prematurely clog the DPF "mesh" filter. 

If in doubt, we strongly recommend that you change the oil in your vehicle to the recommended type of oil. 

An oil change is considerably cheaper than a DPF regeneration - you can rely on us!

Why oils are important and critical for particulate filters

3 Defective/defective fuel injectors

Until recently, faulty fuel injectors have been an overlooked issue when analysing the reasons behind blockages in DPF filters.

Recently, we received a communication from a frustrated driver who was experiencing recurring problems with his DPF blocking. 

After extensive diagnosis, the root cause was identified as a faulty fuel injector that was supplying excess diesel to the delicate air/fuel mixture. 

This excess fuel caused the car to run too rich, which in turn led to excessive soot clogging the filter. 

4 turbo defective

A defective turbo can cause chaos in a modern diesel engine car. 

Anything that disturbs the delicate mixture of air and fuel that causes the diesel engine to emit more black soot than it already does. 

A turbocharger can also leak large amounts of oil into the fuel system, causing the DPF to drown in a sea of engine oil.

How turbo failure affects the vehicle's particulate filter and vice versa

5 Short trips

The way people drive in urban environments, with frequent stopping and starting, is one of the main reasons why many drivers face clogging problems.

Short journeys, low speeds and the constant start and stop nature of driving in built-up areas make it almost impossible to replicate the conditions necessary to carry out active or passive DPF regeneration.

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