[dcb]

The premise is that the old timey diesel pumps are positive displacement. If the length of the injection event can be determined as well as the rpm (both from the same sensor) then it should be possible to get a relative consumption figure of the fuel that was just squirted into the cylinder. That would be the simplest in terms of installation anyway, but you might have to go through a few tanks to get it dialed in (business as usual for most fuel consumption gizmos)