Abstract: An electronic control system for controlling the output of the fuel pump of a turbo supercharged compression ignition engine has a memory circuit which receives an engine speed signal and a fuel quantity signal and provides a derived air inlet manifold pressure signal for use in the remainder of the control system. The memory circuit stores test data relating to the variation of inlet manifold pressure as a result of varying the engine speed and fuel quantity. This overcomes the need to provide a manifold pressure transducer in an engine installation. A delay circuit is provided to compensate for turbo supercharger lag.