Black smoke when accelerating uphill...

... Just driving through switzerland, and experiencing some trouble on motorway hills. 

I have trouble maintaing speed on the hills, accelerating more produces black smoke from the exhaust, and no increase in engine rev's. Turning OD off to increase revs helps. 

Is this just too much fuel / old engine problem. Or something more specific I should have looked at. 

Thanks.

Hmm, sounds like it needs more air. Have you checked teh filter isn;t blocked up a bit, particularly if its up high where the air is thinner and you're going uphill...

Altitude, had the same problem in Austria.

So yes I agree lack of air. Only worry if it does the same when out off the Alps

Put some deisel injector cleaner in the tank...use it regularly for a while...it should clear up some after a few hundred miles