1.  Field of the Invention
This invention relates to an electronic controlled fuel injection system for use in an internal combustion engine having a plurality of cylinders each fitted with a fuel injection valve.  The invention is more particularly concerned with such a system adapted to cut off fuel to at least some of the cylinders during deceleration. 
2.  Description of the Prior Art
Electronic controlled fuel injection systems have already been proposed which are adapted to cut off the supply of fuel to the cylinders during deceleration in order to achieve high fuel economy.  In U.S. application Ser.  No.  34,285, there is described a fuel injection system adapted to resume the supply of fuel to the cylinders when the engine rotational speed falls below a reference level.  The reference level is controlled to increase with an increase in engine cooling water temperature in order to assure stabilized running of the engine. 
During initial deceleration, the throttle valve moves rapidly to its closed position thus causing a rapid increase in intake vacuum.  The increased vacuum draws fuel sticking to the inner wall of the intake passage downstream of the throttle valve or fuel injection valve into the combustion chamber.  This results in poor fuel combustion and thus a rapid increase of HC emissions from the engine.  In order to prevent such poor fuel combustion from occurring during initial deceleration, a dashpot or throttle opener is provided so as to permit the throttle valve to close slowly and the intake vacuum to gradually increase. 
For the purpose of cutting off fuel to the cylinders, the conventional fuel injection system includes a switch actuated when the throttle valve is fully closed for detecting deceleration of the engine.  That is, the system starts cutting off fuel to the cylinders after the throttle valve arrives at its fully closed position.  With a throttle valve associated with a dashpot or throttle opener to delay the arrival of the throttle valve at its fully closed position, the throttle valve will fully close a time after the initiation of deceleration of the engine.  Thus, the engine rotational speed falls below the predetermined level prior to the throttle valve reaching its fully closed position so that fuel is continuously supplied to the cylinders if, for example, the automotive vehicle is brought to a stop with the use of the foot brake. 
In addition, there is a general tendency to frequently use the foot brake where a throttle valve is associated with a dashpot or throttle opener since the engine braking force is not effective just after the engine has been shifted to its deceleration mode of operation.  Accordingly, it is desirable to detect not only the closed position of the throttle valve but also the depression of the foot brake in order to obtain rapid deceleration detection.