Land Rover Repair: smoking, landrover discovery 200, air leaks

Question
I have a Landrover Discovery 200 series J reg TDI.
It starts every time but but it does not rev up properely and is smoking very badly (white smoke) I have had the injectors tested and also checked the bottom pully key way was ok, so the timing is fine as I heard this is a common problem I cant find any air leaks so I am now at loss as what to do next to cure the problem.
Thanks in advance

Answer
Hi Noddy,

could be one of these possible problems:
injection pump timing is incorrect,
valve clearances are incorrect,
wax is forming in fuel.

You could try this:  disconnect the negative terminal cable for about 1 minute.  Reconnect and restart engine. See if there is any change.  

The rev problem usually indicates timing and/or injectors but you say this is ok. strange.

Best of luck,

JohnMc