Hi all 

looking for some advice, My car failed its MOT on Wednesday evening on emissions (Photo1)

Was advised to add some diesel fuel cleaner in and take it for long drive and keep the revs above 3-3.5k. I ragged it to be honest, I did this Wednesday night for a an hour or so,  I noticed lots of black smoke when accelerating but it was gone by the time I finished and seemed to be cleared I repeated this on Thursday Night also but added a full tank of Costco Diesel and some Wynns pre emission fluid also, I did the oil and filter in the summer along side the diesel pump filter & air filter so was expecting it to be fine, I've just had the re-test and the smoke emissions are even worse.

The garage advised to empty out the fuel tank as its the cheap fuel that's causing it, and recommended shell premium and retest ( I'm not a car guy but can do the basics) what else could it be as I'm struggling to understand after 1 day its got so much worse as I said I've been ragging it for two days straight and running the car for an hour before my test.

 

any help would be appreciated.

Injectors are probably knackered.  

Though personally I wouldn't have put more cheap diesel in it before the retest either, that won't be helping.

It's also possible that the DPF is faulty inside as the soot shouldn't be reaching the tailpipe let alone visible in the rear view mirror.  

As above, if you wipe your finger inside the tailpipe and it is sooty (anything more than the slightest layer) the DPF must be melted or cracked, allowing soot to get through which will obviously be a fail?
Also checking DPF pressure differential (if it's low at idle and doesn't increase, then the filter isn't?)
Plenty of backup to that theory here?:

And his other videos...

I have given up with costco fuel - its incredibly cheap in comparison - but it drinks 30% more....