Big Fish Tuning

DPF & EGR Removal

We can offer DPF removal both hardware and software for most cars and vans.

What is a DPF?

A diesel particulate filter (or DPF) is a device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine.

Located within the exhaust system, a DPF captures small soot particles, preventing them from being expelled into the atmosphere. As with any filter it needs emptying periodically and this is done automatically, by burning up the particulates in a process called regeneration.

To meet or exceed European-dictated emissions standards, DPFs have been fitted to most diesel cars for almost a decade and, because they need high temperatures to regenerate, low mileage stop-start motoring can cause them to block.

Common Reasons a DPF can Fail

There are many reasons a DPF can fail, here are some of them:

  • The vehicle is high mileage and the DPF is compacted with fine soot
  • Failed sensors which prevent DPF regeneration
  • Lack of additive in fuel (where fitted) causing incomplete burn off
  • Engine issues i.e. leaking injector, valve stem oil seals, worn piston rings
  • DPF unable to regenerate due to driving conditions i.e. City centre
  • Poor performance tuning
  • Driving in too low of a gear on a motorway disallowing the regeneration to commence

What We Do

At Big Fish Tuning we offer two services regarding DPF removal. We can either do the full works of removal and tuning or simply delete the DPF software from your vehicle post removal. For full DPF removal the filter hardware needs to be removed from the exhaust system and this can be achieved via two methods: 1) A replacement pipe can be fitted (only available on some vehicles) 2) The current pipe can be modified by removing the DPF brick from the inside. Both of these methods are permanent and tested. At Big Fish, we usually remove the DPF brick from the existing pipe, and refit. Following removal, the software needs to be removed from the ECU of the car so that the active and passive regeneration cycles, and any other DPF functions are no longer in operation. This can be done via removing the ECU and programming it on the bench or flashing it through the OBD socket inside the car. For many people, removing the DPF from the exhaust system will be because they have experienced problems with the unit itself. Many filters become clogged as a result of them failing to regenerate and therefore display warning lights on the dashboard and in some cases limiting engine performance. Due to a Diesel Particle Filter being described by dealerships as a ‘wear and tear’ item, vehicle manufacturers will not replace them under warranty and can be costly (usually around £1,500) to replace. We can usually remove the DPF from your vehicle for a fraction of that price.

Removing the DPF from your vehicle is almost certainly going to cause you issues with your MOT. For this reason we would only ever recommend removing the DPF from your vehicle if your vehicle is not used on UK roads (i.e. track cars) or you are exporting your vehicle from the UK

  • Emissions Test

    Petrol vehicles are subject to an emissions test, during this test the exhaust gasses and lambda readings are measured and recorded. Carbon Monoxide (CO), Hydrocarbons (HC) and Lambda (~).

    Diesel vehicles are NOT subject to an emission test, instead they are subject to a simple Metered Smoke Test. During the diesel smoke test the opacity of the smoke is tested, the exhaust gasses are NOT measured or recorded.

  • How will removing a DPF affect the smoke test?

    A DPF is designed to filter out soot from diesel exhaust gasses, therefore a DPF will reduce the opacity of the smoke. So why does a car not fail the smoke test if the DPF is removed? Removing the DPF will not cause the opacity level to rise high enough to fail, in fact, it is very difficult to get a diesel vehicle to fail an MOT smoke test, the fail mark is very high.

    It is worth remembering that DPF’s were not designed to help cars pass the MOT smoke test, they are a result of recent European legislation and the continued pressure on car manufacturers to clean up their emissions. In fact the diesel smoke test was implemented before DPF’s were even applied to cars.

    Why is the fail mark so high? Well this is quite simple, the fail mark is not on a per vehicle basis, i.e. every turbocharged diesel vehicle manufactured before July 2008 has the same fail mark. Therefore modern turbo diesel cars with DPF’s fitted from factory have the same fail mark as turbo diesels manufactured in the late 90’s without DPF’s.

  • What about cars manufactured after July 2008?

    Well recently the MOT diesel smoke test limit for turbocharged diesel vehicles has been halved from 3.00m-1 to 1.5m-1 and this new lower smoke test limit is applied to every vehicle manufactured after the 1st of July 2008.

  • Can you remove the DPF from a car manufactured after July 2008?

    Yes! We have still been successfully removing the DPF from post July 2008 vehicles, and we are yet to have one fail. This just demonstrates how loose the pre 2008 diesel smoke test is and how far modern diesel engine emissions have come. Common rail technology and modern engine management systems have resulted in very clean burning diesel engines which do not require a DPF to pass the new more stringent MOT smoke test.

  • Is it impossible to fail the smoke test?

    No. If a vehicle is in good mechanical condition and has been well maintained then removing the DPF will not result in a smoke test failure. However, a mechanical engine issue which results in the engine running too rich and producing excessive smoke could lead to a failure. In fact, it is quite common for a simple mechanical issue such as a split intercooler pipe or jammed EGR to cause the engine to produce excessive smoke and block the DPF, once the DPF is removed the underlying engine issue often becomes apparent.

  • What about new MOT legislation?

    There is a very simple visual inspection of the DPF unit to ensure it is still in place, because of this legislation we do not fit DPF bypass pipes. Instead, we modify the original DPF unit, discreetly cutting a small window in the top of the chamber, removing the internal filter before rewelding the window and refitting to the vehicle. This way the vehicle still appears to have a DPF fitted and appears unmodified in anyway.

    *Removal of a DPF will almost invariably make your vehicle illegal for use on a public road. This is not legal advice and if you are unsure if this applies to your vehicle, please seek further advice. Please call us to talk in more detail about this. We are happy to only do the software removal if you have a mechanic who is willing to remove the DPF and the DPF brick from the exhaust. For more information on DPFs and how they work, please follow this link for Wikipedia –