VIT is a system which advances the fuel injection timing (i.e. makes the start of injection earlier relative to TDC) as the engine load (and hence the fuel charge per cycle) is reduced below about 85 percent of rated load, so that the maximum combustion pressure (Pmax) is kept at a high, nearly constant value over a wide power range. The purpose is to improve fuel economy and reduce specific fuel oil consumption (SFOC). At high load the injection is retarded to keep Pmax within the safe design limit; at part load the timing is advanced to restore Pmax, which increases the indicated work per cycle and the thermal efficiency, giving a flatter and lower SFOC curve. It is achieved on mechanical engine by a device (e.g. the VIT cam / adjustable fuel pump cone or the VIT mechanism on the fuel pump plunger) which alters the effective timing by changing the position of the delivery valve or the timing piston in proportion to the fuel pump index (load). On electronic engines VIT is achieved by software control of the injection start.

Two-stroke propulsion engine: the end of injection is determined by the fuel injection pump plunger - the delivery valve closes when the plunger uncovers the spill port (or when the pump's fixed geometry ends injection). On a cam-driven pump the injection ends by the mechanical cut-off of the helical edge of the plunger when the spill is opened at a point related to the rack position (load). On electronically controlled two-stroke engines the end of injection is set by the injection duration commanded by the ECU controlling the fuel injection quantity.

Four-stroke medium-speed auxiliary engine: end of injection is controlled by the fuel pump geometry - in a jerk pump, by when the plunger's spill helix/spill port is uncovered as the plunger rotates/traverses during injection, which is set by the rack (load). On common-rail engines the end of injection is determined by when the ECU closes the solenoid valve / triggers the injector needle to close, so the pulse width of the electrical command sets the end of injection. So in both cases the end of injection is effectively set by the amount of fuel injected (load), because injection always starts at a given crank angle and the quantity of fuel determines the duration.

A draw card (or indicator card) is a pressure-volume (P-V) diagram taken from the cylinder by a mechanical (indicator) or electronic (draw card/priman) device. Its purpose is to show the actual pressure variation in the cylinder through the cycle, from which the engineer can assess: the maximum combustion pressure (Pmax), the compression pressure, the mean indicated pressure (MIP) and hence the indicated power of the cylinder, the pressure rise and ignition point, and detect faults such as late/early injection, dribble, blow-by, valve leakage, compression loss, and the presence of excessive back-pressure. It is used to balance the load between cylinders, to check combustion quality, to optimise injection timing/VIT, and to detect developing faults, so the engine can be run efficiently and safely.