General System Description

Fig. 1 Typical digital electronic fuel injection system components:

All 1984-85 Cadillac rear wheel drive models and Eldorado and Sevilles with V8 gasoline engines are equipped with the Digital Electronic Fuel Injection System (DEFI).
Digital Electronic Fuel Injection, Fig. 1, provides a means of fuel distribution for controlling exhaust emissions by precisely controlling the air/fuel mixture under all operating conditions. This is accomplished by establishing a program for the digital Electronic Control Module (ECM), which will provide the correct quantity of fuel for a wide range of operating conditions. Several sensors are used to determine which operating conditions exist and the ECM can then signal the injectors to provide the precise amount of fuel required.
The DEFI consists of a pair of electrically actuated fuel metering valves which, when actuated, spray a calculated quantity of fuel into the engine intake manifold. These valves or injectors are mounted on the throttle body above the throttle blades with the metering tip pointed into the throttle throats. The injectors are normally actuated alternately.
Fuel is supplied to the inlet of the injectors through the fuel lines and is maintained at a constant pressure across the injector inlets. When the solenoid operated valves are energized, the injector call valve moves to the full open position and since the pressure differential across the valve is constant, the fuel quantity is changed by varying the time that the injector is held open.
The amount of air entering the engine is measured by monitoring the intake manifold absolute pressure (MAP), the intake manifold air temperature (MAT) and the engine speed (in RPM). This information allows the ECM to compute the flow rate of air being inducted into the engine and, consequently, the flow rate of fuel required to achieve the desired air/fuel mixture for the particular engine operating condition.