Re: 156 JTD Injectors
If you have replaced a boost pipe, and I asume the one from the intercooler to the battery?
then check the one from the turbo to the intercooler. It is usually covered in oil, so remove it, clean it and stretch and pull it about to check for leaks.
I doubt very much its an injector unless it runs like it missfires, smoke usually indicates bad chipping or a leak from the turbo to the engine.
Does it suffer pooor performance?
What year is the car?
136bhp, 140/150bhp or 20v 175bhp?
Don't chuck money at peoples ideas, before anything, check all the boost pipes, intercoolr etc.
If no luck, fit a boost gauge just to see what boost pressure is getting to the engine, these are 20-30 quid and a cheaper diagnosis than any wally with a big mouth!