MOT Diesel Opacity Test

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Re: MOT Diesel Opacity Test

Post by JohnD »

If the first smoke result was 1.86, which is below the fail limit, why didn't they end the test at that point and give it a Fast Pass?
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Re: MOT Diesel Opacity Test

Post by white exec »

I did wonder that.
Also, I thought the "full throttle to rev limit" tests had been discontinued (some years ago), because of damage risk to over-revv'd engines. Is the thrash test back again in the UK?
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Re: MOT Diesel Opacity Test

Post by myglaren »

I'm glad I leave the MOTs to my mechanic.
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Re: MOT Diesel Opacity Test

Post by MikeT »

JohnD wrote: 28 Jul 2018, 20:31 If the first smoke result was 1.86, which is below the fail limit, why didn't they end the test at that point and give it a Fast Pass?


Doesn't it have to be below 1.5 to get a fast pass?
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Re: MOT Diesel Opacity Test

Post by modmytop »

MikeT wrote: 28 Jul 2018, 22:18
JohnD wrote: 28 Jul 2018, 20:31 If the first smoke result was 1.86, which is below the fail limit, why didn't they end the test at that point and give it a Fast Pass?


Doesn't it have to be below 1.5 to get a fast pass?

Previously yes I believe. My tester told me today that the fast pass is no longer part of the test. Although he said sometimes the computer stops after the first run if less than 1.5, so seems Software still thinks it is!
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Re: MOT Diesel Opacity Test

Post by MikeT »

modmytop wrote: 28 Jul 2018, 22:21
MikeT wrote: 28 Jul 2018, 22:18
JohnD wrote: 28 Jul 2018, 20:31 If the first smoke result was 1.86, which is below the fail limit, why didn't they end the test at that point and give it a Fast Pass?


Doesn't it have to be below 1.5 to get a fast pass?

Previously yes I believe. My tester told me today that the fast pass is no longer part of the test. Although he said sometimes the computer stops after the first run if less than 1.5, so seems Software still thinks it is!


So it has
New or changed inspection

There are new or changed inspections for:

metered smoke test date, which has changed to 1 January 1980
new smoke limit of 0.7m-1 introduced for vehicles first used on or after 1 January 2014
smoke test limits on vehicles post 1 July 2008 will be carried out to either the default standard or the limit on the manufacturer’s plate (where one is displayed)
the option to abort the smoke test if levels are significantly in excess of the specified limit values after one acceleration
fast pass no longer exists
test is passed if the specific limit is achieved after one acceleration, otherwise after 3 accelerations, otherwise after up to a maximum of 6 accelerations
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Re: MOT Diesel Opacity Test

Post by modmytop »

MikeT wrote: 28 Jul 2018, 19:31 There's quite a stark difference between the high and low readings and it's this I think that's resulted in the fail.

(Bold added by me)
"Provided the average of the 3 tests is at or below the appropriate limit in Table 3, and the three results are within a specified tolerance of each other, the vehicle will have passed the test." https://assets.publishing.service.gov.u ... dition.pdf


Previous tests have had results which drop after each acceleration. Would make sense I guess. My first 3 readings do this. It is the 4th reading of 3.2 which is a bit strange, but then the test should not have got that far.
I read that section of the manual also. But never found what the "specified tolerance" was.
If it is due to excessive variation, then why does the results sheet not say so.
It says the mean value is 2.63, and that its a fail as it exceeds 2.5.
However as said earlier where the hell does 2.63 come from????????
Searching the net, I came across one other case where someone was querying their results. Their test ran to 6 runs also, with the average of the first 3 below the limit.
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Re: MOT Diesel Opacity Test

Post by MikeT »

modmytop wrote: 28 Jul 2018, 22:33However as said earlier where the hell does 2.63 come from????????
Just another case of "Computer says no".
Perhaps the 2.63 is the derived mean of the specified-tolerance-adjusted-values instead of the average of the absolute readings shown?
As it results in a fail over otherwise seemingly good average readings, I imagine it would be helpful to know why tolerances are specified.
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Re: MOT Diesel Opacity Test

Post by Oldpug »

white exec wrote: 28 Jul 2018, 20:27 If in doubt, for any diesel smoke test:
- avoid supermarket/budget fuel
- use a remedial dose of Miller's Diesel Power Plus, or Wynn's Diesel Fuel Treatment (these are two that do actually work)
- and an Italian run, to shift accumulated soot.


I agree.

Many years ago I used to work on these Peugeot XU diesels every day and very rarely had one fail. If one had been neglected a bit I would put a flushing agent in the oil and diesel clean in the tank (Forte products) then go for a 5000rpm road test. Change the oil and filter and off to the MOT.
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Re: MOT Diesel Opacity Test

Post by white exec »

My long-time favourite MoT tester in Rudgwick, West Sussex (used David from 1971 to 1998), if confronted with our BX19RD, always used to ask if it "had been on a run". On the couple of occasions it hadn't, he would offer to take it on a bit of blast along the A281, and then test it; it always passed. :)
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Re: MOT Diesel Opacity Test

Post by JohnD »

MikeT wrote: 28 Jul 2018, 22:18 Doesn't it have to be below 1.5 to get a fast pass?


On the OP's car, because of it's age the pass mark is 2.5 for a non turbo and 3 for a turbo engine.
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Re: MOT Diesel Opacity Test

Post by JohnD »

modmytop wrote: 28 Jul 2018, 22:21 My tester told me today that the fast pass is no longer part of the test.


Methinks your tester talks rubbish. If a vehicle engine produces a figure which is below the limit on the first try, the engine has passed. What would be the point in revving it again. In April when I took my C5 for MOT, he revved that once and the certificate was printed "Fast Pass"........................ The smoke analysers which they use in MOT stations work automatically, telling the tester what to do and when to rev. IMO either the tester is at fault or the machine is broken. If the results were as you report, the machine should not have gone beyond three revs. I would submit an appeal.
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Re: MOT Diesel Opacity Test

Post by MikeT »

JohnD wrote: 29 Jul 2018, 14:25
MikeT wrote: 28 Jul 2018, 22:18 Doesn't it have to be below 1.5 to get a fast pass?


On the OP's car, because of it's age the pass mark is 2.5 for a non turbo and 3 for a turbo engine.
Yes, I agree but the way I read the actual test process, a FAST PASS requires a reading of 1.5 or less, regardless of the engine. If that fails, then it uses engine specific limits but it's a moot point as it appears they did away with the FAST PASS when new rules came into force in May.
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Re: MOT Diesel Opacity Test

Post by RichardW »

It doesn't exist in words anymore, but if the first reading is below the specified level for the car (which depends on age and whether there's a limit on the VIN plate) it passes(*) - so effectively a fast pass. The OP's car should have passed this, so there is something wrong with the computer, programming, or operator!!

* see the info from the manual Marc posted above: viewtopic.php?f=4&t=60594#p581786
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Re: MOT Diesel Opacity Test

Post by MikeT »

Again, assuming I'm understanding the process correctly I can't disagree Richard but there's something very odd about all six readings.
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