As for modern diesels,I believe that VW are having to abandon their PD technology as they can't get it to meet the new even stricter emissions regs,and also a lot of older diesel engines aren't
charged,as now a
is pretty much standard,which can give the impression that it smokes a lot.
I'm not sure it's PD technology specifically... While VWs seem to be what I'm noticing smoking lately, it might just be that Passats are so common in the fleet market. I have definitely seen others - I've seen quite a lot of the Traffic 1.9dCis or the Vauxhall/Nissan equivalents billowing smog, especially on the hills round here, and my Dad's L200 (which is serviced no-expense-spared at Mitsubishi main dealers) is pretty bad.
Anyway, just because a car's got a
is no excuse for it to be over-fuelling, even off-boost. Perhaps in an old fashined mechanically injected diesel where the pump compensates for boost before the
's fully spooled up, but there's certainly no excuse in a modern computer controlled engine. Plus, almost all passenger cars from the mid-90s on are TDs. The Lag 1 is a rare exception in a car that was common as an N/A diesel. I've also seen a few N/A 405s about and Meganes, but if you look at the Mondeo, Vectra, Passat, 406, 306, Astra, etc, while some of them may have been offered in N/A versions, but very few of them around.