I have noticed that my 6.9L will really roll coal @1800 rpm. Is that normal? Is that the rpm where the pump dumps fuel? Anything above or below and it runs reasonably clean
Your 1800 RPM has nothing to do with ROLLING COAL per se. It's just that you "mashed" the throttle at that RPM and your feeding more fuel than the engine needs, as the RPM's increase, naturally the engine needs more fuel to keep speeding up and the smoke decreases when the level of RPM's is equal to fuel needed. The IP supplies fuel to the injectors to fill the injector for the next injection event thru the return line. the Hi pressure from the IP only triggers the injector to open "and dump it's load", so the more fuel thru the Hi pressure line, the wider/longer opening the pintle is, and feeds more fuel to the precup than it can burn during that stroke, hence the black smoke. Timing of this event in relation to fuel injection and combustion is relevent. Just a simple explanation. Mel would have a more technical explanation.
The IP is always dumping fuel thru the return line, as long as the lift pump is supplying more fuel than the engine is using, that's what helps keep the IP from overheating.