The paper describes briefly the fuel control possibilities in an injection system fitted to an Otto cycle engine. Whatever arrangement is chosen, it must be able to measure accurately the air flow to the power unit. For a particular engine and at a given engine speed, the throttle angle will indicate directly the air being aspirated per unit time. Thus a control following a surface whose height indicates the fuel requirement based on both throttle angle position and engine speed will give a unique fuelling value under all conditions. The work described employs this technique and explains how a digital computing method is used to transpose the value of throttle angle and speed into a fuel quantity injected in the engine intake tract every cycle. The engine work required to obtain the surface is described and it is also explained how a sophisticated ignition timing surface can be devised.Factors determining the type of electric to hydraulic interface required are discussed. Although unaided fuel injection cannot meet the Federal 1975 and 1976 exhaust pollution requirements it can make a worthwhile contribution to the problem by enabling the engineer to supply his afterburning device with a gas stream of closely controlled quality.