The engine control system is responsible for control modes for fuel control and ignition for all possible engine operating conditions. However, there are a number of distinct categories of engine operation, each of which corresponds to a separate and distinct operating mode for the engine control system. The differences between these operating modes are sufficiently great that different software is used for each. The control system must determine the operating mode from the existing sensor data and call the particular corresponding software routine.
For a typical engine, there are seven different engine operating modes that affect fuel control: engine crank, engine warm-up, open-loop control, closed-loop control, hard acceleration, deceleration, and idle. The program for mode control logic determines the engine operating mode from sensor data and timers
In the earliest versions of electronic fuel control systems, the fuel metering actuator typically consisted of one or two fuel injectors mounted near the throttle plate so as to deliver fuel into the throttle body. These throttle body fuel injectors (TBFIs) were in effect an electromechanical replacement for the carburetor. Requirements for the TBFIs were such that they only had
to deliver fuel at the correct average flow rate for any given MAF. Mixing of the fuel and air, as well as distribution to the individual cylinders, took place in the intake manifold system.
The more stringent exhaust emissions regulations of the late 1980s and the 1990s have demanded more precise fuel delivery than can normally be achieved by TBFI. These regulations and the need for improved performance have led to timed sequential port fuel injection (TSPFI). In such a system there is a fuel injector for each cylinder that is mounted so as to spray fuel directly into the intake of the associated cylinder. Fuel delivery is timed to occur during the intake stroke for that cylinder.