Diesel Smoke Tests

[CitroJim]

Does anyone know how the MOT smoke test limits are applied to different engines? Are there different ones for different engines?

I ask as when my 2.1TD went through the MOT, it was subject to a smoke limit of 1.5 l/m. Xac recently had his 1.9TD MOT'd and he appeared to have been subject to a test limit of 3.0 l/m.

My 2.1TD passed at 0.03 l/m whereas Xac's passed at 1.92 l/m.

Now, had my 2.1TD, say, been fitted with a mechanical pump, as I would plan to do if the EPIC failed, it might well fail if the lower limit was applied.

So, are the older XUD9s and so on tested to a different limit than say, the later 2.1TDs and HDis?

[KP]

http://www.dvtani.gov.uk/uploads/custom ... eaflet.pdf

[CitroJim]

http://www.dvtani.gov.uk/uploads/custom ... eaflet.pdf

Brilliant Will, thanks! Google never was my friend for finding stuff like that

All is now completely clear (no pun intended..) So if it's clean and passes at 1.5 l/m (Fast Pass) then fine. Otherwise it's tested at 3.0 l/m...

The engine will be accelerated up to governed
speed and the smoke density measured.
Engines that emit very little smoke and achieve
a meter reading of 1.5m-1 or less will pass the
test after the first acceleration. However, if the
test is not passed on the first acceleration a
further two accelerations will be carried out.
The average of the three acceleration readings
will be calculated and if the reading is at or
below 2.5m-1 for non-turbocharged engines
or 3.0m-1 for turbocharged engines, the
vehicle will pass this element of the test.
However, if the average is higher, a further
acceleration will be carried out, and the average
of the last three readings will be calculated. This
will continue up to a maximum of six
accelerations. If the average of the fourth, fifth
and sixth accelerations is higher than the
appropriate level, the vehicle will not pass the
test.
In addition, vehicles may be refused a
certificate if the exhaust emits excessive smoke
or vapour, to an extent likely to obscure vision.

[CitroJim]

Just noticed this in the quoted text above..

This will continue up to a maximum of six accelerations.

Or, until the cambelt breaks....

[citronut]

that is the case unless the cam belt when ping on the first run of the test

regards malcolm

[KP]

Like i said Jim i think the car would be a wrong un to fail on veg

[nick]

My 2.1TD passed at 0.03 l/m

That's a very good result Jim. I think some of the latest diesels with particulate filters would struggle to better that.

Mine was over the fast pass at 1.70 last time. Having said that I think my Xsara is a little smokey for an HDi. I've long suspected I have one injector on the way out.
My old Xantia 1.9TD was better, I think it used to average around 1.40 .

[Xaccers]

Cassy's was on weekend on v-power (wasn't able to get to costco) and is coming up for a service.

[Peter.N.]

It is very easy to adjust the fueling on the Bosch pump Jim and I have found they tend to get leaner as they get older so are unlikely to fail, the performance also deteriorates of course, but so slowly you don't notice it, but a little 'tweak' will soon bring it back again.

[nick]

It is very easy to adjust the fueling on the Bosch pump Jim and I have found they tend to get leaner as they get older so are unlikely to fail

Ahh, I owned my Xantia TD for several years and that would explain why the emissions always reduced very slightly from one MOT to the next!

[Sl4yer]

I've read about the possibility of cam belt failure since this test was introduced. It doesn't seem to have caused too many problems.

Surely a turbo diesel (which almost all diesels are nowadays) won't be running much boost, since the engine isn't under load. So the cam belt is unlikely to break - in fact the pressure on it will be less than in a N/A diesel because of the reduced compression ratio on the turbo engine. Will somebody please tell me why I'm wrong?

James

[Peter.N.]

Well, there certainly don't seem to have been many cambelt failures, but what puts a cambelt under stress is not so much the engine load as the rate of acceleration. If the engine is reved without a load it accelerates much more rapidly, so the cam shaft and pump are trying to play catch up.