Electronic Fuel Injection

Electronic Fuel Injection refers to a system of components using electronic sensors and controls to accurately measure the amount of fuel required by an engine, and then deliver it to the engine.
EFI became popular in the 1980s. Practically all modern cars today utilize electronic fuel injection in some form. The Z-car adopted electronic fuel injection in 1975 on the 280Z.

On the Z32

The Z32's electronic fuel injection system was relatively standard in terms of operation. It uses strong components (high-volume fuel pumps, for example), but it worked like practically any other EFI system from the time.
The basic mode of operation is as follows:

• Incoming air is metered by the MAF sensor and sent to the ECU.
• The throttle position is measured by the TPS and sent to the ECU.
• The rotational speed and position of the engine is measured by the CAS and sent to the ECU.
• The oxygen content of the exhaust gas is measured by the O2 sensors and sent to the ECU.
• The speed of the vehicle is measured by the VSS and send to the ECU.
• The temperature of the engine is measured by the Engine Temp Sensor and sent to the ECU.
• Using the above factors, the ECU determines the correct timing and fuel maps to refer to.
• The ECU refers to specific cells in the selected timing and fuel maps to determine the correct ignition timing and fuel injector pulse-width.
• The ECU fires the ignition coils (and thus, spark plugs) and fuel injectors at a specific time and duration as determined using input from the above sensors.

Fuel System

Unlike carburetion, which uses a venturi effect to draw the necessary amount of air into the combustion chamber, EFI systems are designed to very accurately meter the incoming amount of air and inject a specific amount of fuel in for the given situation.
Depending on the amount of fuel necessary (using the sensors mentioned above), the ECU has the Fuel Pump Control Unit change the speed of the fuel pump to supply the desired amount of fuel. The fuel pump, housed in the fuel tank, sucks up fuel and sends it to the engine's fuel rail, allowing it to fill the fuel gallery in which the injectors are housed. At the end of the fuel circuit, the fuel pressure regulator acts as a dam and allows a varying amount of fuel to return to the fuel tank. This is to maintain the fuel pressure in the fuel rail at 43.4psi over the intake manifold pressure. When the ECU fires an injector, power is sent to the fuel injector for a brief period of time (the length of which is determined by the ECU depending on the amount of fuel required). When the fuel injector receives power, a solenoid inside opens up a valve, allowing a small amount of the pressurized fuel to escape, spraying it into the lower intake manifold, where it is "inhaled" into the combustion chamber.
After the combustion is completed and the exhaust gas released, the Oxygen Sensors read the oxygen content in the exhaust gas in order to fine-tune the amount of fuel required for a sustained driving condition. This helps the ECU to determine and precisely modify the amount of fuel necessary to achieve a stoichiometric air:fuel ratio (14.7:1).