Car going in tomorrow for its Terraclean, I have asked them to do a before and after Emissions printout. They say they always do a before, but told me there are too many chemical fumes present to get a true after test, straight after treatment, they tell me they will do the after test after I have driven the car for a couple of days.
Does this make sense?

smoke and mirrors....  Pete
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2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand Sold
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Sold
2002 L322 Vogue 4.4 V8 Epson Green (Fatty Offroader) Sold
-Click for Project Fatty off roader-

Waste of money, IMHO

Slightly different thing but I had them do my sons DPF which had clogged irreparably according to the dealership who wanted £1600 for a new one but they did a terrific job. Completely fixed the issue and for a fraction of the price. I'd say in my experience they can certainly clean the internal workings.

I done the same with a pressure washer

DPF was choked solid, and the car wouldn't run. Couple hours washing it out, took it for a blast to regen itself, with no issues

I tried it out of interest on one 100k TDV8 and was not impressed. It will not clean/fix faulty EGR's.

My "smoke and mirrors" comment was about their claim that they can't do a test straight after because "chemical fumes present".... what chemicals!!!! they advertise that it is super refined fuel that goes through the system, there is no mention that they use any other chemicals and indeed if they did you would have to capture and dispose of the exhaust gasses whilst cleaning...

Leave any car at fast tick over for an hour (which is what they do) will effect the emission anyway...!!!

A lot of the deposits in the engine that cause trouble have no connection with the fuel, deposits from EGR's are fed into the engine upstream of the injectors so even neat cleaning fluid will have no effect on them...

All Terraclean will do is clean the injectors and maybe remove a small amount of carbon from the intake valves... you can get the exact same result with a £5 injector cleaner from Halfords...

Do't believe all the hype from some tall bloke who doesn't cut his hair and wears orange gloves.... he has no engineering or mechanical qualifications, he's just an enthusiast who got famous when he made that motorised settee... Pete
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2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand Sold
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Sold
2002 L322 Vogue 4.4 V8 Epson Green (Fatty Offroader) Sold
-Click for Project Fatty off roader-

As above, the "chemicals" smell suspiciously like Kerosene, which is the main ingredient in diesel injector cleaner

They do two versions. The one I tried went into the air intake system near the airbox and exited the exhaust......

I had the other, fuel system cleaner in through the HPFP and injectors

More to the point, what are the OP's thoughts

Well I had it done today, car is still running great, so I can't say I notice any difference. I am going on a 200 mile trip tomorrow, towing a caravan, so that will give me a better idea of any advantage, mpg etc.

I must admit I had it done, because I am only doing short stop start journeys.
I didn't like the misfire I had at the end of the last DPF regeneration, so if it happens again, I can say: I have had the top end cleaned up. If the misfire never reapears I can think the Terraclean solved the problem.

After running for about 250 miles since the Terraclean, I can't say I notice any difference to the running of the car. But it's a bit like my choice of diesel, I use Shell V power, thinking it is good for the engine. Others tell me it's a waste of money.