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Mot emissions fail at 0.9

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#1 peacehavenboy


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Posted 23 November 2019 - 11:07 AM

Hi. Just took my C4 Grand Picasso 1.6 hdi 2009 for mot.
Everything was fine + no advisorys apart from a fail on the emissions?
They have to have a reading of below 0.5 and mine were 0.9
The car has done 136000 miles has had a recent major service with Mobil 1 Esp oil as well.
I commute to work mainly carriageways a round trip of 60 miles and have used a bottle of dpf cleaner recently with 20L of fuel in the tank and the day before the mot put a whole bottle of 2 shot diesel cleaner in and filled the tank up.
Question: I have booked a retest for next saturday and plan to get the fuel in the tank down to about a quarter or less then add a bottle or two of Wynns extreme emissions reducer followed by an hours thrashing up the motorway before I pull up at the mot station for the retest.
Do you guys think this will do the trick or any other better ideas.
Thanks and regards

#2 Marvin


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Posted 23 November 2019 - 11:50 AM

I'd spend the money,  not on additives etc, but on diagnostics to find out why your emissions are nearly twice the permitted maximum;  there must be some tangible reason for this which,  if fixable, would be a permanent solution.

"Life? Don't talk to me about life....."

#3 cris1117


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Posted 23 November 2019 - 01:03 PM

Unless things have changed the emission test for a diesel is better described as a smoke test.

Having driven diesels for the best part of 40 years I have faced this problem many times.

Soot builds up in the exhaust system, some is blown out by normal driving a little more by a thrash down the motorway.

When you go to the MOT station the examiner will rev the engine hard which will blow the rest of the soot out and you will fail the MOT.

So what you need to do is what the examiner will do and rev it hard before he does.

Find somewhere quite and give it several good hard revs lasting about 2 seconds a time you will see clouds of black smoke come out the exhaust on the first couple of revs then it will start to blow clear, your now ready for the MOT.

Since I learned this trick some 30 years ago I have never had an emission fail.

Don't bother with additives in the main they have little or no effect.


#4 peacehavenboy


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Posted 23 November 2019 - 03:20 PM

Thanks for the advice will give it a go

#5 Ozzie


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Posted 26 November 2019 - 05:57 PM

check the tester is setting the smoke limits correctly.

On my recent MOT my limit was set too low and the car failed.
I complained and the car passed on a retest with the correct limit set.
The tester blamed the machine.

From the MOT manual

For vehicles first used between 1 July 2008 and 31 December 2013 the smoke limit is:

the level specified on the manufacturer’s plate
1.5m-1 if the manufacturer’s plate is not available

the plate value could be in the VIN number or on a separate label in the engine bay,

worth checking , a limit of 0.5 seems very low , even post 2014 cars have a default limit of 0.7.