Big Spriter Proplem

[sprinters3]

I have had a proplem with my sprinter for months but now its doing my head in I have a Light on the dash EDC or something like that I know what this is I have to call mercedes benz anyway when that start coming on it started kicking out loads of gray smoke and will only do about 60 mph foot to floor. but some times its great and there no smoke and will go over 100 mph anyone help me out here not to assed about the light at the moment.

Things I have tryed

New disiel lines/fitters/pumps clean tank out and and refilled

Swaped computers on the van

The proplem am having comes and go

[4xpaws]

For the record... I contacted sprinters3, coz my EDC lights coming on on my Vito. He still hasn't got it fixed.