My sisters 2.5TDI T4 failed its MOT yesterday on "diesel smoke" issues..

The tester has mentioned something about revving the nuts off the thing before dropping it off for testing...

Are there any other known methods to help reduce the particulate that comes out of the back end?

Is this an actual machine tested particulate count thing, or is it just what the tester sees?

The turbo looks and sounds in good condition and it doesnt use much oil....

[Edited on 26/3/10 by tegwin]

It's generally a symptom of high power diesels that never get pushed hard and soot builds in the exhaust. Then on the smoke test they get reved hard and out it all comes.
For best results, flush the oil and then change oil and filter... then... thrash the arse off it. Find a big hill and go up in second, full throttle on the rev limiter (this isn't easy given the power and torque). Keep lifting then flooring it. Repeat untill it's cleared the soot from the system.

Not exactly sympathetic to the engine, but a dam good thrashing never did anybody any harm!!

adrian

edit... yes, it's a machine tested smoke test.

[Edited on 26/3/10 by adithorp]

Yup. Rev it nice and hard to blast soot out the system. Diesels have good torque so rarely need to be thrashed so oil can collect....

The "rev the nuts off it before dropping it off" also works well for petrol cars as it gets the cat nice and toasty warm.

My Volvo has similar issues and I find that whenever I so stints of working a bit further from home it gets a lot better.

When replacing the starter motor last weekend, the air intake pipe had to be removed and we found a 5mm or so layer of soot on the INTAKE pipes. Looks like it's something to do with the emission control system that recycles exhaust gasses when cold.

I've cleaned out the easy to reach pipes and will be givign it an oil and filters change this weekend. A couple of damn good thrashings should get it back on track. I could take the entire intake system apart and clean it, but the intake manifold is integral to the cam cover, which also has the injectors and a load of sensors etc. in it - the benefits don't outweigh the effort IMHO.

Does it have a particulate filter? if so a good hours run at motorway speeds is needed to clean it out

A feature of modern low emmision diesels which get used for slow town work.

Its just done a 1000 mile trip back from the alps... But driven by my old man... so it will barely have used any power atall...

Think I need to go give it a service and then a proper itallian tune up!

My A4 Tdi has failed before but its quite old so relatively simple. So I ran the engine from a bottle of injector cleaner direct then poured the rest in the tank.

Took it up and down the motorway but also up steep hills in high gears to get heat in the injectors and exhaust to dislodge deposits.