I don't know much about the 606 but the one thing I know is that smoke from a diesel is caused by the timing being off a lot, for instance, 180 deg because the TDC used was the TDC of the exhaust stroke, not the intake stroke. If timing is correct, then there is an air supply problem. Not having a turbo should not be an issue if at idle. If too much fuel was injected, the engine would just run faster. Does the 606 have any kind of device in the intake track that could reduce the amount of air going into the engine? I know my 602 has an air valve in the intake and it can cause the engine to smoke if it sticks closed. It is used inconjuction with the EGR valve. Maybe the injection pump is putting in more fuel but the ecu is restricting the air intake for some reason.
Just think, more fuel = more power if there is enough air. Now enough air = black smoke (un burned fuel). At idle the turbo is not an issue.

Paul

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84 500 SEL (307,xxx miles)