DPF Removal vs MOT Restrictions

January 16, 2014

Emissions Testing
Petrol vehicles are subjected to emissions testing, in the test the exhaust gasses and readings from the Lambda sensor are measured to see if it is all in specification.
Diesel vehicles are NOT emissions tested, they are only subjected to a basic smoke test, this doesn’t record or measure exhaust gasses only the opacity of the smoke produced.
How will DPF Removal affect a smoke test?
A DPF filter is designed to collect the soot particles from the diesel exhaust gasses, so this reduces the opacity of the smoke. This would make you think that if the filter is removed it will fail the smoke test? But removing the DPF does not cause the smoke level to raise high enough to fail the test. 
This is due to the fact that the recommended smoke levels are very high, DPF Filters are not designed to help cars pass MOT restrictions they are created for European Legislation and the continuous pressure for car manufacturers to improve their emissions.
The fail mark is set at a high level as it is a general guide line for all diesel vehicles tested, all turbocharged diesel vehicles pree July 2008 has the same fail mark.
For diesel vehicles after July 2008 the set mark has been halved from 3.00m-1 to 1.5m-1.
Can you remove a DPF Filter from a car manufactured after July 2008?
Yes removal and MOT passes are still possible to post July 2008 diesel vehicles, because we are yet to have a failure, this just goes to prove how far advanced diesel engines have become, common rail technology and modern engine management systems have made diesel engine burn their fuel cleaner and do not require a DPF filter to pass MOT regulations.
Is it possible to fail a smoke test?
No failure of a smoke test is not possible if the vehicle is in good mechanical condition and has been well maintained then removing the filter would not result in a failure of the smoke test. but a mechanical engine that will make the vehicle run to rich will result in a failure, as this will create excess smoke because of burning to much fuel.
This quite common for simple mechanical defects to affect this, like a split intercooler pipe or jammed EGR valve, this can also block DPF filters and once removed the engine issue becomes more apparent.
What about new MOT Legislation?
The new MOT Legislation is expected to come infrom Febuary 2014 as a VISUAL inspection of the DPF filter, this will be a very basic inspection to ensure that is still in place, because of this at West Coast Remaps we do not fit by-pass pipes like some companies, we use the and modify the original DPF casing cutting a small window in to it and retracting the filter inside before rewelding and refitting to the vehicle, this way the DPF seems to be untouched.


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