Black smoke after releasing exhaust brake?

[Stafford]

Hi all, any theories on why my truck is suddenly putting out a puff of black ssmoke after releasing the exhaust brake?
I let it sit for 2 weeks undriven, then changed the water separator. Thats all i can think of!

Its an older model, direct injection turbo 4bd1t motor.

 

[Aussie Iron]

This I had when the exhaust brake butterfly on mine (Canter) was sticking. Example :- driving along with accelerator down - release accelerator - exhaust brake comes on - put foot on accelerator to give it some power but exhaust brake doesn't go off straight away and releases a couple of seconds later with a cloud of black smoke.

Maybe,

Dan.