Well, I still vote to fix it all at once, but I like to learn so it would be interesting to hear what the mechanic thinks... Tspringer, could you pose some questions to him?
Which problem is causing the black smoke and low RPM
Did the bad injection pump wreck the cylinder by over fueling and is still over fueling causing black smoke and loss off power.
Is the fuel being made by just washing
past the rings or does he think the pump is leaking internally?
Or is the low compression making the black smoke and low RPM?
If he were to only fix one of the two problems, which first? Would it be the low compression or the injection pump?
Basically get his idea of the sequence of events
. What went wrong and what caused what?