MOT Changes May 2018, Diesel emissions

In May this year (2018) the MOT test is under going some changes, some of these relate to older vehicles and different classes, but the single biggest change that is going to directly affect road users are the changes to the MOT Diesel emission test.

In a move designed to clean up the air we breath, the MOT test is now going to be alot more strict on Diesel models, this is for both new and old cars and also for cars fitted with and without a DPF.

We will start with Diesel models fitted with DPF filters, these were phased in, dependent on model, from around 2006 onward, the easiest way to tell if a BMW has one is:

  • If the exhaust points down at the ground = No DPF Fitted
  • if the exhaust points straight out = DPF fitted
  • All BMW diesel models from mid 2007 will have a DPF

A DPF is fitted to control and reduce the amount of particulates that exit the vehicle around towns and cities, these particulates are then burnt off on longer journeys such as, A-Roads and Motorways where speeds tend to exceed 50mph.

However, short stop / start driving and other engine related faults can cause these filters to become blocked. Now there is a correct way to resolve this problem where the vehicle is diagnosed and then the filter cleaned ( this is what we do ) OR there is the incorrect way, which involves garages cutting open the filter, removing the innards and then changing the cars software in a way to prevent any warning lights. ( This is something we do not do! )

From 20th of May, if there is any evidence the DPF has been tampered with, the vehicle will FAIL the MOT and the DPF will require replacement.

A secondary effect of removing a DPF is that vehicles will occasionally put out some smoke, when started and the under acceleration.

From 20th of May, If smoke of any colour can be the seen, the vehicle will FAIL the MOT

Diesel emission testing changes

As well as the visual checks and inspections the regulations regarding emission testing is being changed and tightened, this is going to affect all diesel models both those with and without DPFs fitted.

Currently diesel engines are tested to a standard default value, this can be quite generous on older cars and even cars emitting some smoke will pass these default values. So for example it is common to see a 2008 2.0 Diesel engine with the DPF removed still passing current test limits quite comfortably. 

From 20th of May these "Default value limits" are being replaced by the emission value that the manufacturer ( in our case BMW ) has printed onto the chassis plate/sticker, this is the plate that shows axle and towing weight information, the number will be in square box.

So for example:

  • 2005 BMW E91 2.0D M47TU engine no DPF , current test limit = 3.0m-1  , After 20th of May = 1.57m-1 
  • 2007 BMW X3 2.0D M47TU engine with DPF, current test limit =3.0m, After 20th of May = 0.51m-1 
  • 2008 BMW E93 3.0D N57 engine with DPF, current test limig = 1.5m-1 , After 20th of May = 0.57m 

As we can see the first vehicle which is non DPF the value is almost halved, this shouldn't be a problem for a well looked after car, It may be a problem for cars with faulty injectors or  faulty EGR valves for example.
The Second example shows a huge reduction in limit, this will be an issue if the vehicle has had the DPF removed or if the vehicle is not running correctly.
The Third example shows a reduction but not quite as dramatic as the first and second, as it is a post 2008 vehicle where the limits are lower anyway, but it is still nearly 2/3rds lower, again if the DPF is removed from this vehicle it will more than likely fail this test.

What can you do to prevent a Diesel emission MOT Fail?

First of all if the vehicle should have a DPF, make sure it hasn't been removed, if you are unsure, us or a local specialist will be able to advise you further.
If you know, or have your self had the DPF removed, you will need a get a new filter fitted as well as the Engine ECU software corrected, any specialist will be able to assist you with this.
If you had the filter removed due to blocking, the car will require a diagnostic check to establish the original cause of the blocking to prevent further problems.

Secondly, regular servicing, fuel cleaners and premium fuels can all help improve economy and performance as well as reducing emissions.

A premium fuel such as V-Power or BP ultimate will create a cleaner combustion, thus lowering emissions, as well cleaning or keeping clean injector spray nozzles, again this can lower emission readings.

A Fuel cleaner / treatment ( We stock and recommend BG245 Diesel treatment ) is a high strength diesel fuel cleaner, and works hard to treat fuel systems and injectors, removing hard baked on carbon from injector spray nozzles. A clean fuel injector will reduced the amount of fuel injected at any given RPM - Less fuel injected = lower emissions. For best results BG245 should be used for a fuel tank of fuel ( or around 500 miles )

Regular servicing, Diesel engines are inherently dirty compared to petrol engines, and thus they have a tendency to sludge up even when sticking to manufactures servicing schedules. To avoid this we recommend oil changes at every 10k miles, with an added engine flush. An engine flush will help remove carbon deposits and free up sticking piston rings, this in turn will increase engine compression, which in turn will increase performance whilst lowering fuel consumption and emissions. 

BG 3 Can treatments, target both the engine and fuel system.

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Induction cleaning for all Diesel models

If you'd like to go a step further we can also offer an induction clean service, this involves running a chemical cleaner through the intake system of your Diesel. It targets carbon build up on intake ports and valves, hard baked carbon deposits within the combustion chamber cylinder and through the turbo and exhaust system. It also includes the addition of the engine flush treatment and the fuel treatment. 

This is the best single way of restoring lost performance and shifting carbon that has built up in the cylinder head. The cleaner we can get an engine the more efficient, powerful and reliable it is going to be. It is important this service is carried out as preventive maintenance to keep everything running smoothly. 

This service was recently carried out on a 2005 320D model at 97k miles, the car had no fault codes and appeared to run "ok" . Post clean the car picks up alot earlier under acceleration and is alot smoother, it is also returned better MPG, since the clean.

A Full induction clean treatment service can take 3-4 hours in total, and includes an Engine oil and filter change.


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