I have a 4D55 recently rebuilt engine. The injection pump, injectors and turbo have not been rebuilt. Under normal driving condition with minimal load the truck does not smoke. If I'm going up a hill or under acceleration there is a constant stream of black smoke coming out of the exhaust. Could this be that the injection pump timing is off? Turbo wore out? Injectors in need of rebuild? The other night I tore the injectors apart and cleaned them (they had some build up in them; fixed my miss when first started up when cold).