Had loads of aggro with injectors, even though car had had £1800 worth of pump and injectors just before I bought it and car's only done 78K miles. Developed v.bad diesel knock and smoking on start-up a month later. Delphi tested the injectors and said they were fine, yet swapping two cured the knock and reduced the smoke!! Cost me £600, and it's still not quite right now.

Plus I've got a serious boost leak and can't find it, despite stripping the car and swapping just about everything... no fault codes, and non of the usual suspects are at fault. Plus I've got a hub nut that works its way loose no matter what we do, and takes out wheel bearings which are £60 a pop. I'm on my third bearing, and 5th hubnut. Got an outer CV to swap in next, so fingers crossed for that.

Give it a go. There's a lot of hype about additives, and lots of different ones to choose between. Just don't expect it to be a magic fix for your car!