Emissions fail on MOT

[Mottie]

Take it for a run before the test, get it as hot as it will get and thrash the f'king nuts off of it.

It passed with a 0.17 reading. Stress over. Next time i will drive it hard before the mot

 

[Avocet]

My experience of this, suggests the gunge is of a much drier, less fluid gunge. Once it is deposited, nothing much will shift apart from mechanical scrapping or chemical removal. I have seen EGR bores, reduced by the build-up, to less than 1/3 of the air path through them.

Logically, I cannot see how it might affect the emissions, unless the EGR etc. become very seriously restricted by the gunge.

My workshop manual makes no mention of the possibility of gunge building up, or any need to ever clean the EGR + manifold + intake at all. Being already aware of the problem, when I bought my car - I stripped the lot down and gave it a thorough clean out.

I've kept a close eye on emissions at each MOT, but it has always been so clean, the inspector has thought his tester had developed a fault, the first few times he did the MOT. I note they no longer offer the emission's data printout, following recent MOT's.

Once the oil has baked-on, then yes, only mechanical scraping will shift it. However, I'm talking about while it is still liquid. Mrs. Avocet used to have a Nissan X-Trail. She drives very gently. Once a month, or so, I would "drive it like I stole it" (sometimes with a heavy trailer n the back too). On the owners' forum, there were so many horror stories about blocked inlet manifolds and EGR valves, that when it hit 100,000 miles, I thought I'd best have a look inside the EGR. To my great surprise, it looked like the tailpipe - a thin layer of black dust that would wipe off with my finger! This is definitely a problem that affects gently-driven cars more than it affects ones that get thrashed.

It affects smoke emissions, because when the tester revs the living daylights out of it, (I think) it does that "scouring) of the inlet tracts, and dumps a load of crap out of the exhaust - unfortunately, right when the meter is stuck up it!

 

[Avocet]

You can get a 'bypass' for some engines, which simply blanks the exhaust from entering the inlet, but it increases the Nox.

Which is worse, a badly running engine with a gunged up inlet, creating lots of smoke/ or a clean inlet where the EGR is bypassed and more Nox - is anyone's guess.

They're both bad, of course! Ideally, we should be aiming for minimal smoke AND minimal NOx! However, recent research is suggesting that particulate emissions from tyres is MUCH worse than particulate emissions from exhausts.

 

[Avocet]

i looked into a blanking plate - which was available - but a few saab forums reported issues - and the engine fault light was on - so had to remove before a MOT ........
Anyway , just my 2 penny worth, doesnt help solve the OP problem

My son-in-law has an old 1995 Skyline - petrol , which he has to take on a run and thresh to get really hot and warm - to get through the emissions - and if they cant get onto the mot , straight away , as happened at last mot - it fails and then he has a retest.......

That will be a different fault - they don't test petrols for particulate emissions.

 

[Avocet]

Ive checked the oil this morning and i have a bit of black over the top of the dipstick, but there is clearly a black band around the lower half and it finished exactly on half way. So i am assuming this dipstick is showing it is correctly filled. Again I dont do this that often.

I have changed the oil filter as well, but not the air.

As to my driving i really dont drive it that fast. It just isnt that type of vehicle. So the distance the computer tells me i have left in the tank after a fill up is about 720 miles. Now i have been driving harder these kast few days it is saying 540miles. So faster driving has lost me about 200 miles per tank. the question about all this pollution stuff is who is being more green ? Driving slower or driving faster ?

Different sorts of "green". That's one of the most difficult problems to get across to politicians! You have CO2 emissions - bad for climate change, but CO2 isn't toxic. High fuel consumption = high CO2 emissions. However, carbon MONoxide is highly toxic. Unburned hydrocarbons (HC) and oxides of nitrogen (NOx) are also pretty poisonous. We kill about 10 times more people each year simply with the pollution from our cars (and other sources) than we do by running them over! All cars (including electric ones) can be environmentally good in some ways and bad in others.

 

[norseman]

They're both bad, of course! Ideally, we should be aiming for minimal smoke AND minimal NOx! However, recent research is suggesting that particulate emissions from tyres is MUCH worse than particulate emissions from exhausts.

Anyone told Khan that?
Will he be banning anything that runs on tyres

 

[Avocet]

Anyone told Khan that?
Will he be banning anything that runs on tyres

No, it's relatively new research, and a big problem. Not just tyre, but friction lining particulates. EVs don't have clutches, of course, and they're lighter on their brakes because they regenerate for some of their braking, but they are heavy on tyres.

The numbers are fairly staggering, though. compared to tailpipe particulates from a brand new Euro 6d car, what comes off the tyres is about 1800 times worse than what comes out of the tailpipe!

Gaining traction, losing tread Pollution from tire wear now 1,850 times worse than exhaust emissions — Emissions Analytics

By some distance, the research Emissions Analytics published in early 2020 claiming that tire particulate wear emissions were 1,000 times worse than exhaust emissions generated the most feedback of any subject we have tackled so far – feedback that was a mixture of surprise and scepticism

www.emissionsanalytics.com