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Discussion Starter #1
Pleased to say my Lag I sailed through the MOT bar a couple of rubber exhaust mounts.
The only thing that they were concerned about was the emissions - thus they had to run some emissions treatment through it & blast it up & down the road. I was informed that maybe I hadn't be driving the car 'hard' enough!? He mentioned that on diesels it is a good idea to sometimes run the card really hard to clear out all the carbon deposits, i.e. if you see lots of black smoke coming out of the exhaust - run the car hard to blow it all out.

Is this true or was the guy just talking gibberish? Does seem to make sense.
 

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Discussion Starter #3
Oil was changed in December - along with a load of bent valves, amongst other things - timing belt failure! :(
 

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This is something I see on a daily basis.:)

The main reason for diesel(especially turbo diesel) engined cars failing an emissions test is the car not being driven hard enough.Once a month,I would take the car out for a drive onto a decent section of road,wait for the engine to come up to normal temperature,then floor the accelerator in second and third gear till the engine hits the govenor!.It sounds a bit extreme,I know,but this will clear the system out and will ensure that the engine is running efficiently and that the car will go through the emissions test come MOT time.You will be surprised at the amount of black smoke that you'll leave behind!

I'm not a fan of diesel additives as all they do is raise the burn temperature inside the cylinder and can actually do more harm than good........

Hope that helps.:)
 

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The MOT guy was absolutely right this problem area is one of the reasons that there have been concerns with diesels whilst undergoing the test.
What is recommended is that the car is driven hard so that it is quite 'hot' immediately prior to the test or/and various diesel cleaners may be used for the vehicle to pass the emissions limits. Obviously only really effective if the emission test is done immediately on arrival at the test centre. However, in most cases it is the final part of the test!
I believe this indicates the ludicrousness of this test if it is only done at the MOT. After all most diesels operate at fairly low revs as it is almost impossible to get up to proper speed unless on a motorway.
When I check the average speed on my 'computer' it sometimes barely reaches 30mph in the area that I live and that also includes some motorway driving.
 

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Discussion Starter #6
Many thanks for all the advice. You learn so much on this site - brilliant.
Like you say will take her out for a bit of a 'burn' now & again, wake the old gal up :d
 

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my family has run many high mileage diesels for years. we almost always drive them lightly. when going for MOT we always make sure the engine is at operating temperature(very important) and take them to the rev limiter in 2nd gear and hold it there for 5-10 seconds/untill the rear view mirror shows you arent filling the road with smoke while en route to the test centre. Never had one fail on emissions.

(well there was one but we took the air filter out, retested and it was fine)

also VERY important to make sure the car isnt left idling for any length of time before the emissions test.

other re test tricks are to fidle the turbo waste gate to give a higher boost pressure. this is risky for blowing holes in pistons and head gaskets but is generally ok for MOT test because the engine is lightly loaded for short periods of time
 

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When having diesels MOT'd I always change oil, oil filter, and air filter - haven't had an emmissions failure yet. I live in Northern Ireland where the emmision tests are much more stringent than mainland UK but at the request of public demand they test the exhaust emmisions on arrival - so it's up to the driver to ensure the engine is well-warmed up. As said in a previous post engines are easier to warm up when placed under load - sitting stationary and reving them like mad isn't a good idea (diesel's generally don't like it). I hear people whingng when their car fails on emmissions but when you think about it - if it fails it's not operating at its most efficient - so it probably using more fuel than it should - it's the old story maintain your engine well and in the long run you will save money (ask any commercial haulier).:)
 

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I can't seem to clear the 'check emissions' message by revving hard....it appeared on holiday in France and I drove 2k miles on motorways over the fortnight. Any further thoughts?
 

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Turbo diesels don't like sitting in traffic, they get all choked up.
I failed a test earlier this year, I was advised to fill up with the cleanest deisel at the petrol station and blast it around the block for 20mins (took it to the red line on each gear change - gave her a damn good thrashing!!). Went straight back for a retest and she passed!

PS I was sensible in finding a suitable thrashing location :)
 

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Hi Renfault - yeh you just can't beat a good Italian tune-up. You said it failed the ommisions test at MOT. Have you any idea on what it failed on - was it CO or hydrocarbon levels that were over the top.:)
 

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Hi madnoel10, can't remember sorry, got the report here somewhere, will dig it out and will get back to you.

PS Having a bit of a 'mere' with clio emissions right now so busy elsewhere on this wonderful life saving & pocket saving site.
 

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Hi Renfault - yeh you just can't beat a good Italian tune-up. You said it failed the ommisions test at MOT. Have you any idea on what it failed on - was it CO or hydrocarbon levels that were over the top.:)

A Diesel would have a job to fail on CO or HC's........

Only smoke opacity is tested.:)
 

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Sorry but I forgot only smoke opacity is tested on the mainland UK - whereas over here in Northern Ireland it a full blown sample testing - possibly coming to a place near you soon:)
 
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