Fuel injection fuel control system

A fuel injection control system for an internal combustion engine of the spark ignition type including an air-gas induction passage open at one end to air at ambient pressure level and connected at its other end to the engine combustion chamber to be subject to manifold vacuum changes therein, a throttle valve rotatably mounted for movement across the passage to control the air-gas flow therethrough, an exhaust gas recirculation (EGR) system including EGR passage means connecting engine exhaust gases to the induction passage above the closed position of the throttle valve, an EGR flow control valve mounted therein for movement between open and closed positions to control the volume of EGR gas flow, an engine ignition timing control device movable to vary the timing, an engine speed responsive positive displacement type fuel injection pump having a fuel flow output to the injector that varies as a function of changes in engine speed to match fuel flow and mass air flow through the induction system of the engine over the entire speed and load range of the engine to maintain the intake mixture ratio of air to fuel constant, an air/fuel ratio regulator operably connected to the pump and movable in response to changes in intake manifold vacuum connected thereto to vary the fuel output of the pump to maintain a constant air/fuel mixture ratio, a first vacuum circuit having a source of vacuum operably connected in parallel flow relationship both to the EGR valve and to the ignition timing control device for providing an adjustment of the ignition timing whenever the EGR flow is adjusted so as to compensate for the change in air/fuel mixture charge burn rate whenever the quantity of EGR gas in the mixture charge is varied, a second vacuum circuit connecting the source of vacuum to the air/fuel ratio regulator for modifying the regulator movement that normally is made in response to changes in intake manifold vacuum alone so as to compensate for changes in the concentration of oxygen in the gas mass flow to the engine whenever the rate of EGR flow changes upon movement of the throttle valve, to thereby maintain a constant air/fuel ratio, the second circuit including first vacuum controlled means connected to the regulator for modifying the movement of the regulator as a function of driver demand signal as indicated by the open angle of the throttle valve and as a function of engine load conditions, to change the pump output to provide the constant air/fuel ratio at times as well as at other times an air/fuel ratio other than the constant air/fuel ratio, and the first vacuum circuit including second controlled means operably interconnecting the EGR valve and throttle valve and engine ignition timing device.