MOT Diesel Opacity Test

[modmytop]

Apologies if not correct place for this post. My 20 year old Pug 306 1.9D failed its MOT today on emissions.
Suspected it was going to when I heard the 4th, then 5th then 6th test! Anyway didn't look at the figures until I got home.
They are:
1.86, 0.92, 0.61, 3.20, 0.84, 2.21.
As it's an early (1997) normally aspirated diesel, so the limit is 2.5.
The final result was 2.63, hence declared a FAIL.
My understanding of the test was/is if the average (mean) of the first 3 runs is less than the limit, it is a pass.
If not, you keep testing up a total of 6 runs, taking the average of 3 consecutive runs.
Now the first 3 runs above have an average of 1.13. Well under the limit of 2.5.
Even the last 3 runs average 2.08.
I intend to speak to the testing station tomorrow, but in the mean time, do you guys have any idea why I got a fail?
I have no idea where the final figure of 2.63 came from!
Cheers
Bri

[white exec]

Not unknown for an inexperienced tester to test a diesel (a) unsympathetically and (b) incorrectly.
Had this a year ago on XM 2.5TD, with a fail by a young tester, and a pass (with a figure just 10% of the previous) two days later. The second test was done by the (state-run) test Centre's senior technician, who effectively apologised for the mishap.

Will be interesting to read detailed replies here.

[Hell Razor5543]

I think 2.63 is the IQ of that MoT person!

[EDC5]

It it possible to loosen the throttle cable on the injection pump by moving the metal clip?

I believe this was a trick for the modified 1.9 DTurbo 306's that prevented the tester from applying full throttle.

[RichardW]

If the figures are right, it should have passed on the first go:

The vehicle has passed the opacity test if any of the following happens:

the first acceleration showed that the smoke level was at or less than the limit for the vehicle
the mean smoke level from the first 3 readings was at or less than the limit for the vehicle
the mean smoke level from any consecutive 3 readings was at or less than the limit for the vehicle

So, he's either mis-read the figures or given you the wrong print out. I'd take it back and insist they retest the emissions only, and issue a pass!!

[modmytop]

Spoken to garage (not actual tester yet). Told its all done by the machine. Will speak to tester direct. Its already had 3 extra unnecessary acceleration runs. I don't want the old girl to suffer any more.

[JohnD]

My 20 year old Pug 306 1.9D failed its MOT today on emissions.

Apart from colour, my daughter owns a similar car to your own. Her's is also a 1998 1.9D 306 Peugeot which I look after and get it's MOT done. I happen to take all our cars to the same test station and over the years, the test has thrown up some strange results. All the smoke tests have all been done on the same analyser by the same operator. When the 306 was tested at 51000 miles, the first acceleration was 1.46, so a Fast Pass. The following year at 54000, the first acceleration was 4.95; the 2nd was 3.78; the 3rd was 3.29; the 4th was 2.71; the 5th was 2.18 and the 6th was 1.88, scraping a pass with 2.21.

How can there be so much difference over just three thousand miles on tests carried out by the same operator. Factors which come to mind are a) Was the car left ticking over for a longer period? b) Did I put less Millers additive in the fuel? c) Was the oil in the sump at a different level? d) I rule out engine temperature because at both tests the car had done 10 miles down the motorway just prior to the test.

Before the test, is the tester supposed to purge the engine before the first acceleration?

Regarding the OP's test result, usually the results reduce over the course of the test. I've never seen one where the highest figure is at the middle of the results.

[Peter.N.]

Giving it a good thrash on the way to the MOT to remove some of the soot in the exhaust system should help bring the readings down.

Peter

[GiveMeABreak]

Here's the relevant bits from the latest test manual:

Before the test, check the maximum smoke level limit for the vehicle and enter the required details into the diesel smoke meter.

For vehicles first used before 1 July 2008, the limit will be one of the following:

• the level specified on the manufacturer's plate
• 2.5m-1 for a non-turbocharged engine – if it's not stated on the manufacturer's plate
• 3.0m-1 for a turbocharged engine – if it's not stated on the manufacturer's plate

For vehicles first used between 1 July 2008 and 31 December 2013, the limit will be one of the following:

• the level specified on the manufacturer's plate
• 1.5m-1 – if it's not stated on the manufacturer's plate

For vehicles first used on or after 1 January 2014, the limit will be one of the following:

• the level specified on the manufacturer's plate
• 0.7m-1 – if it's not stated on the manufacturer's plate

If the smoke level is displayed on the VIN plate, it will be a number, usually in a box (as below), and often positioned in the bottom right corner of the VIN plate.

How to test:

1. Make sure the engine checks are satisfactory.
2. Make sure the engine temperature is above 80 degrees centigrade or at its normal
3. operating temperature whichever is lower.
4. Make sure you've removed any oil temperature probes.
5. Increase the engine speed to around 2,500rpm or half the maximum engine speed – use whichever speed is lower.
6. Keep the engine at this speed for 30 seconds – this should fully purge the inlet and exhaust system.
7. Increase the engine speed slowly to maximum engine revolutions (revs) to check that the governor is working properly
8. Once the engine speed has stabilized or it becomes clear that the governor isn't working, release the pedal and allow the engine to return to idle.
9. Stop the engine and prompt the meter to do a zero check.
10. Insert the meter fully and securely in line with the gas flow.
11. Restart the engine.
12. Following the meter prompts, press down the accelerator pedal quickly and continuously so that the engine reaches full fuel position in less than one second.
13. Hold the engine at full fuel position until a release prompt is given and immediately release the accelerator pedal.
14. Allow the engine and any turbochargers to return to idle.
15. After the first acceleration read the smoke level displayed on the meter.
16. If the smoke level is above the limit for the vehicle, carry out 2 further accelerations.
17. If the mean smoke level is still above the limit for the vehicle, carry out further accelerations up to a maximum of 6 in total and read the smoke level display on the meter after each acceleration.

The vehicle has passed the opacity test if any of the following happens:

• the first acceleration showed that the smoke level was at or less than the limit for the vehicle
• the mean smoke level from the first 3 readings was at or less than the limit for the vehicle
• the mean smoke level from any consecutive 3 readings was at or less than the limit for the vehicle

If the smoke levels from the first acceleration were significantly higher than the limit, you can choose to abort the test.

On vehicles fitted with a diesel particulate filter, also check that no visible smoke is emitted from the exhaust during the metered check.

Engine malfunction indicator lamp
Turn on the ignition and check that the engine malfunction indicator lamp (MIL) illuminates and then goes off. On some vehicles it will be necessary to start the engine before the MIL goes off.

'Dangerous' & 'Major' are all Fails.

Defect	Category
Smoke opacity levels exceed the manufacturer’s specified limit.	Major
Smoke opacity levels exceed default limit	Major
Exhaust emits excessive smoke or vapour of any colour to an extent likely to obscure the vision of other road users	Dangerous
Exhaust on a vehicle fitted with a diesel particulate filter emits visible smoke of any colour	Major
Emissions test unable to be completed	Major
Emissions test aborted because smoke levels are significantly in excess of the specified limit values	Major
Engine MIL inoperative or indicating a malfunction	Major

[modmytop]

Spoke to tester. He said all done by machine. It calculates the mean of the readings. I asked had the software been updated recently. In May this year, but has tested many diesels since. But could there be a bug for say non turbo diesels that hasn't been found yet. He did mention after the test that there was vibration or knocking at high revs. He thought the machine could be taking that into account. But there is nothing on the results other than good
(apart from the 3.2) opacity readings. As i said before i can not get the result of 2.63 from any of the readings. How long would it take to complain to VOSA?

[GiveMeABreak]

He probably doesn't know how to take the mean average - as I can't get 2.63 from any combinations of those figures you supplied.

If you appeal they will first look at the figures again before it gets lodged - as they won't want any blots on their copy book unnecessarily - get them to explain how they arrived at that 2.63 value - it they cannot do so, they will likely do another emissions test for you free and check the readings again. I suspect they will apologise and pass it this time!

[white exec]

Ask for it to be tested again.
As Peter suggests, do a 10-minute fast hot run (a gear lower than normal to keep revs up to 3000 or so for several minutes) just before the test.
As everyone has said, those listed figures suggest everything is actually ok.

[modmytop]

Im entitled to a free retest within 10 days. However the previous results have shown it may be deemed a fail even with good results! I took her for an Italian tune up in the hour before the test. Planning an oil an filter change before it goes back in. However as said i dont see why the old girl should be put through that again. And what if it gets low results and still fails?

[MikeT]

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

[white exec]

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.