Originally Posted by MTUpower

I don't think many here understand that a engine which has the ability to "roll coal" is not a poorly running engine. It's an engine that has the ability to inject far more fuel at a low RPM than the engine can burn. At higher RPM the turbo boost is high enough that the fuel is burned and no "coal" is emitted. If you've ever watched a tractor pull you'd understand. The ability to inject large amounts of fuel has a direct relationship to higher total HP. It's akin to showing other modified diesel owners that your engine is powerful.

Older (or even newer) diesel which consistently smoke while under load or in between gears are not "rolling coal"; they are running poorly. The usually need more air by either standard maintenance (air filter change) or some other upkeep. Excess smoking in a diesel engine is most of the time directly related to fuel/air ratios; it's either too much fuel or not enough air.