Emission readings

[civvie]

Daughter has just passed her MOT with her Clio, ( using this forum as there isn't much action on the Renualt one) the emission reading were;

Test Limit applied 3.00 l/m

Absorption coefficient 2.29 l/m 2.53 l/m 2.83 l/m

Mean Absorption coefficient 2.55 l/m Zero drift 0.01 l/m

Mean absorption coefficient after correction 2.54

Are these readings on the high side? she has had problems with emissions before on Mot's.

She have a 1.5 turbo diesel, 53 plate mileage about 45000, non intercooler, new air filter and oil etc, had a blast down the motorway before the MOT.
Is this something that can be looked at without a course in electronics if needed.

Thanks

Steve

[CitroJim]

Seems a tad high Steve but it may have been due to prevailing atmospheric conditions.

Does it smoke appreciably when it's given beans? Can you see smoke if you do the snap idle test as carried out by the MOT man?

[civvie]

Jim,

Thanks for the reply and confirming my suspections. All I can tell you is when I followed her to the MOT place the other day, there was white exhaust smoke coming out of the back of the car, ( just like someone is on choke) I assume that was because the engine was cold.

she had a emission light come on last year some time and she took it to the Renault dealership, there it seems they took the EGR valve off and gave it a good clean plus sorted out other fault codes. Mind you it has taken me a year to find this out, asking daughter to do something like find a receipt is like talking to the cat. Can't at the moment check the snap idle test, but will give a go when she next visits. Don't know what else to check, the air filter is new, and its too bl00dy cold to be under a car at my age. Any ideas?

Steve

[CitroJim]

The EGR valve could hold the clue Steve. If it is not 100% perfect it might be responsible for the high emissions.

I don't know the answer on a Renault but on most PSA diesels, the EGR valve can be disabled fairly easily and if you could do this, a trip to a garage for a quick emissions test would prove one way or another.

Diesels normally don't "steam" anywhere near as much as a petrol engine. What you may be seeing is unburned fuel rather than steam, suggesting one cylinder might be a tad down on compression. If valve clearances are easily checked/adjusted, make sure all the clearances are within spec.

If this and the EGR valve comes out OK then a leak-down test would be a good next step to confirm all compressions are good.

[civvie]

Thanks Jim,
will have a look at the EGR when it gets a bit warmer, at least she is ok till the next MOT.

Thanks for replying.

Steve