Curious about my MOT smoke test results?

[SDHA4SLine]

Hi,

Had my MOT yesterday, all good no advisories and passed

Looking at the smoke test results and Its clear to see its way below the max permitted but I'm curious if it was good, bad or just normal for a 2.0tdi (PD170) as I've not really a clue what 'zero drift' 'mean value' & 'FPT mean value' are?

Print out below..

Edit: also is an idle speed of 880rpm a little high?

 

[SootySport]

Does it matter? It passed

 

[SDHA4SLine]

Well not really but I am curious about how mine will fair when the MOT's are tightened up. As I understand it the max figure is well above what most modern diesels would ever reach but there are many rumours that in the next year or so things will change regarding smoke test max limits based on your car age and spec. So just wondering if its on the mark or if it should be better than it currently is.

 

[ESD1711]

No idea what they actually mean or what you 'should' be getting - but looking at where you are with regards to what you've gotten and what the max allowed values are - i'd be massively surprised if you had anything to worry about.

If I remember when I get in from work though - i'll dig out mine from last month for comparison.

 

[SootySport]

If they do tighten up on emissions, then I would have thought it would be for new cars meeting Euro V1. Don't worry about yours.
Having said that, it is time to ditch DERV's for us mortals, unless you are a taxi driver doing 30k. miles a year, I certainly won't be buying another. The wifes A3 is a pre DPF motor thankfully, still have the egr to clean every year though.
Cheaper to drive petrol motors now.

 

[desertstorm]

I think the idle speed seems a little high, but only but 20-30 rpm. On EDC15 ECU cars you could alter the idle speed with VCDS adaption on the ECU . Not sure if you can do that on your car.
The zero drift is I believe a check of the tester. They leave it measuring fresh air rather than the exhaust to make sure that it's reading is stable.
There are two possible tests, one is an average test and the other is fast pass. Thats what FPT means Fast Pass Test.
To get past the Fast pass it needs to be less than 1.5 on the first acceleration run which yours was.
If it exceeds 1.5 on the first run, they do 2 more runs and then average the 3 readings and that needs to be less than 3.0.
A car has to be really bad to fail a smoke test.
I found the last MOT for mine and it was 0.69 for a 300bhp plus 3.0 V6 TDI. The wifes 2005 75BHP 1.4 TDI recorded a 0.75 reading.
So 0.61 is good, no where near a fail.

http://www.ukmot.com/MOT test/Emissions - Diesel.asp

Karl.

 

[gary_a4_quattro]

I would doubt that, if any maxixmum allowable values were lowered, changed or tightened up, they would be applied to all vehicles. I would imagine they would only be applicable to the very latest generation oil burners. The current values would remain for vehicles of our build years I'm sure

 

[SDHA4SLine]

I think the idle speed seems a little high, but only but 20-30 rpm. On EDC15 ECU cars you could alter the idle speed with VCDS adaption on the ECU . Not sure if you can do that on your car.
The zero drift is I believe a check of the tester. They leave it measuring fresh air rather than the exhaust to make sure that it's reading is stable.
There are two possible tests, one is an average test and the other is fast pass. Thats what FPT means Fast Pass Test.
To get past the Fast pass it needs to be less than 1.5 on the first acceleration run which yours was.
If it exceeds 1.5 on the first run, they do 2 more runs and then average the 3 readings and that needs to be less than 3.0.
A car has to be really bad to fail a smoke test.
I found the last MOT for mine and it was 0.69 for a 300bhp plus 3.0 V6 TDI. The wifes 2005 75BHP 1.4 TDI recorded a 0.75 reading.
So 0.61 is good, no where near a fail.

http://www.ukmot.com/MOT test/Emissions - Diesel.asp

Karl.

Excellent, very well explained. Thanks Karl

 

[ESD1711]

Having said that, it is time to ditch DERV's for us mortals, unless you are a taxi driver doing 30k. miles a year, I certainly won't be buying another.

See, I was kinda convincing myself the other way the other day - but I guess it really depends on what kinda cars you're comparing.

I noticed the other day that the difference in cost per litre between petrol and diesel was just 3p now. I'd say that in some cases that makes running a diesel car even more beneficial if you're comparing against an older petrol car which is only benefitting from 3p per litre of cheaperness, but costing more in a lack of mpg'ness.

Compare something like a Mk4 Golf GTi against a GTTDi and its as good a time as ever to be driving a diesel.

But I can see your point when you look at the 'modern' petrol cars which are capable of getting dieselesque type MPG's out of a fuel which is cheaper.

 

[ESD1711]

For comparisons sake, my numbers were:

0.02
0.84
0.84

 

[SDHA4SLine]

For comparisons sake, my numbers were:

0.02
0.84
0.84

Looks similar to mine then

 

[SootySport]

See, I was kinda convincing myself the other way the other day - but I guess it really depends on what kinda cars you're comparing.

I noticed the other day that the difference in cost per litre between petrol and diesel was just 3p now. I'd say that in some cases that makes running a diesel car even more beneficial if you're comparing against an older petrol car which is only benefitting from 3p per litre of cheaperness, but costing more in a lack of mpg'ness.

Compare something like a Mk4 Golf GTi against a GTTDi and its as good a time as ever to be driving a diesel.

But I can see your point when you look at the 'modern' petrol cars which are capable of getting dieselesque type MPG's out of a fuel which is cheaper.

If you consider the extra cost of a DERV against a petrol car and the fact that DERV car maintenance is much higher with the introduction of EGR's , dpf's and a turbo charger (especially when they go wrong) then petrol car wins. If you are doing short journeys then the dpf is not doing it's job, it has to go into forced re generation, burning extra fuel to do it's job.
Some Local Councils are soon to introduce a DERV tax of about £100 a year for the privilege of owning a DERV, Islington being one of them.
Haven't noticed the narrowing gap between diesel and petrol prices though, maybe it's because of the threat to the future of the DERV they are talking about in the NHS and DOT.
Maybe time to reverse your conversion to Derv's

 

[SDHA4SLine]

If I read last years results correctly, rather worryingly my smoke test is 6 times worse than 12 months ago !

 

[desertstorm]

Have any changes been made to the engine/ exhaust etc since last year ?. 0.1 is pretty low.

 

[SDHA4SLine]

Hmm, just a few, most of this was done trying to find the reason why its chucking smoke out.

Both n75 's
MAP senser
MAF sensor
EGR valve
coolant temp sensor
fuel temp sensor
fuel filter
air filter
Inlet manifold actuator.
Turbocharger
Coolant thermostat

Car has had many scans since these parts have been fitted no faults found other than one intermittent egr fault which was cleared and has not come back.

Having said all this it has now been diagnosed that my car has a "very slight" compression leak (yet to be confirmed if its a inlet or outlet valve or piston rings) so I suppose this could be the reason yes?

 

[SDHA4SLine]

Dragging this up from the depths but just to follow up....

This years mot smoke/opacity (or what ever its called) test attached. Test seems slightly better than last years down from 0.61 to 0.51 Also looks like the maximum permissible Mean value limit has halved from last year???

 

[CoolAsIce]

The limit is 3.00 for cars before July 2008, and 1.50 for cars after this date. 0.6 is average really.

I find cars smoke more that don't ever get driven hard, generally a quick Italian tune-up down the road clears the smoke.

Most modern cars with dpf's don't even register on the smoke test at all, we usually end up lightly kicking the machine just to give a reading for a print-out, otherwise it won't give a print out.

 

[SDHA4SLine]

The limit is 3.00 for cars before July 2008, and 1.50 for cars after this date. 0.6 is average really. .

So they screwed up on mine then? its a 2006 and the mean limit looks like its a 1.5 limit?

Not that it matters as its passed but...

 

[CoolAsIce]

Yes they've tested it under the wrong one it seems. But like you say it doesn't really matter as it's passed.

 

[stu-evans]

Your numbers are a lot better than mine..... Mot test last month was 1.41 (they tested mine against 1.50 as well). Car is a 2007 140bhp... Although it is running a non-resonated S4 exhaust set up, so not much to stop the smoke on its way out!.

I am wondering now whether I should be checking anything on the engine as yours seems so low in comparison??

 

[SDHA4SLine]

Probably as you say your exhaust doesn't help matters but I wouldn't be spending money until its a fail (still confused by our being tested at 1.5)

As for where to look, id say if your car is running nicely and its passing the smoke test then don't worry about it. For this reason I'm reluctant to suggest something for you to look at (that and I have a history of sending people on a wild goose chase ). Maybe someone like @desertstorm could suggest something for you to investigate (he knows his stuff)

 

[desertstorm]

As above I wouldn't worry about the smoke test and the absolute readings that you get if your car is running OK and it passed.
The thing to do is make sure the engine is nice and hot when it's tested and that you have given it a good clear out as well . If the engine is well serviced with a good air filter and no obvious issues it should pass OK.
I take my cars for a good run to warm them up before taking them for an MOT, I will also do an acceleration run through second and third gear to give them a bit of a clear out.

 

[stu-evans]

Great, thanks both! Car runs great, has far better pull with the S4 exhaust, and is serviced frequently (filters changed ahead of schedule)..... Quite happy to leave it be if there's nothing obvious/easy that may reduce the smoke!