NCT Query - Smoke

Redline it at idle for 30 seconds or so. And drive it extremely hard to the red line. You don't have to drive fast, just drive it hard in 1st and 2nd gear. See if that gets rid of the smoke.

Always drive to the nct in 3rd with plenty of revs in a older diesel

I always throw the full bottle in if it is a diesel. Never had any problems.

If it is a diesel, fill up with HVO too. If it still fails, you have a further issue.

Is it a petrol or diesel?

More than likely an issue with an intercooler pipe leaking or the intercooler itself.

Are you getting black smoke when you accelerate real hard? Did you put HVO into it

before the test? Or Diptane?

Use diptane and HVO and try again. If that doesn't bring it down you have fuel/air problem I would think.

Every fuel additive is. If a diesel fails the extremely relaxed NCT smoke test then clearly it's something wrong with the engine.

You probably need to actually drive it in the red. I had problems last year, and took three attempts to get through. I use Dipetane on a semi regular basis, as well as extra before the NCT. Last year I even added petrol to the diesel fuel after a few people recommended it. Eventually passed.

This year I drove 80km on the motorway, in third, in the red, the day before the test. Then third gear for the 12km to my local test centre. Passed at 1.120 and the limit was 1.5.

Pretty obvious you have dpf deleted because underlying issue . Was risk you took failing nct .

Only option i see to pass it put liter of petrol into it with haft tank of diesel

Stupid accusation tbh. A DPF delete doesn't even cause excess smoke

If you are so certain that a DPF delete would cause excess smoke, please explain how pre 2011 diesel cars with no DPF emit no smoke? If what you are saying is true, any pre 2011 diesel would be smoking heavily.

The point of a DPF is to capture harmful soot particles which are invisible to the human eye, not to reduce smoke.