Growing up i remembered getting stuck behind an older diesel they would smoke like crazy pulling up hills. Ive never seen my rig smoke once. Why would my truck not? Have anything to do with the ULSD? I'm not complaining. Don't really want the smoke. Just wondering
It's primarily due to the fact that our engines are electronically controlled, and the total fuel delivery is being constantly adjusted depending on total air mass charge going into the cylinder.
Old diesels, even turbo ones, are non-feedback mechanical systems. Fuel delivery by an injection pump meant that the more throttle applied resulted in more fuel delivery. As the vehicle was driving through increased load, the resulting air charge would decrease but fuel delivery would not, resulting in less complete combustion of the fuel charge. Some mechanical diesels, such as the very elegant Mercedes 617 turbo, had an atmospheric compensation system called the ALDA system, as well as vacuum-fed fuel trimming that would try to adjust fuel charge under load. Guys like me, in the interests of power and as a byproduct get a little more coal, remove the tamper seal on the ALDA and trick the mechanical system into believing that atmospheric pressure is much higher than it really is... resulting in more fuel delivery under all conditions. Tailgaters can also be dealt with by stepping on the pedal repeatedly and not allowing the turbo lag to catch up to the extra fuel.
EDIT: This is also why guys like my friend with a 91 12V have such an easy time getting coal... they can adjust delivery on their stock VE pumps quite easily [/EDIT]
The only way to get the 7.3 to roll coal is to increase fuel delivery by way of programming. Stock, as well as most aftermarket tunes, will not have excess fuel... maybe a little bit more in tow tunes but I've only ever noticed a bit of coal when in tow mode and shifting to a higher gear under load.