First thanks to all concerned for some great tips on here.
I thought of passing on this tip it may be helpful to someone looking for advice about smokey exhaust.
I have a 2002 Asrtavan 1.7 dti isuzu engine, from cold it was fine then soon as temp reached 85 it decided to start pumping out a lot of black smoke and went into limp mode, so i popped in a new air filter but it continued to belch. After a nervous and expensive visit to a main dealer who hooked it up to computer and came back with 3 faults.
I asked well which one needs replacing? response all 3 of them, after i had picked myself up from the floor, i asked him if he had auditioned for Britains got talent, and then i promptly walked out.
Not to be defeated i drove to another main dealer who came out with the same story, so i decided to clean EGR myself this gave a slight improvement but still smoke was belching once van was hot.
I had to make a delivery to a small family run garage in a rural location, they seemed nice guys so i decided to ask them for an opinion on the problems i was having, he grinned and connected up his snap on computer to find no faults showing assumed main dealer had cleared them, turned it on to diagnostics and after a couple of minutes said it's not a sensor problem it's mechanical, turbo boost is well down on what engine is asking for hence lots of unburnt fuel i.e. black smoke.
2 minutes later he found a cracked jubilee clip on the bottom of boost hose coming from turbo, he replaced it said call it a £5 and suggested a good blow out down motorway to clear the system out.
I was shocked but paid up and left, the response from the throttle was amazing like a new engine smoking a little but very responsive, after agood thrash down the M5 it appears to have blown out all the soot and back to normal.
Main dealers huh!!!!
I hope this may be of some help to anyone suffering similar problems