General Information

Engines 4A-FE and 3S-FE are equipped with a multi-point injection system. This Electronic Fuel Injection (EFI) system consists of three basic systems: the electronic control system, the air intake system and the fuel system (Fig. 4.1.1.).

Fig. 4.1.1. EFI System General Diagram, where:

1. Fuel filter 2. Fuel pump 3. Fuel tank 4. Circuit opening relay 5. EFI main relay 6. Ignition switch 7. Diagnosis connector 8. "Check engine" warning light 9. Battery 10. Electronic Control Unit (ECU) 11. Distributor (JJA) 12. Fuel control connectors (*c) 13. Variable resistor (*c) 14. Instrument panel 15. Speed sensor 1 16. Neutral start switch (*a) 17. Rear window defogger relay 18. Rear window defogger switch 19. A/C amplifier (*b) 20. Intake air temperature sensor 21. Throttle position sensor 22. ISC valve 23. A/C VSV for idle-up (*b) 24. Engine coolant temperature sensor 25. Vacuum sensor 26. Fuel pressure regulator 27. Injector 28. Knock sensor (*d) 29. Lambda sensor (*d) 30. Three-way catalytic converter (*d) (*a) - with automatic transmission; (*b) - with air conditioning; (*c) - without catalytic converter; (*d) - with catalytic converter

The Electronic Control Unit (ECU) receives, among others, signals on engine speed, throttle valve position, residual oxygen content in the exhaust gases, absolute pressure in the intake manifold and intake air and coolant temperatures. The electronic control unit controls, among others, signals to the injectors (injection duration), the ignition distributor (ignition timing), the diagnostic system (signals of sensor failures) and the fail-safe function.

The fuel system has an electric fuel pump that supplies fuel at constant pressure to the injectors. The injectors spray the calculated amount of fuel into the intake air ports in accordance with signals from the Electronic Control Unit (ECU). The air intake system supplies the appropriate amount of air.

The Electronic Control Unit (ECU), which controls both the ignition system and the fuel injection system, is located inside the vehicle behind the instrument panel. On models with the 4A-FE engine it is located behind the left side of the instrument panel on right-hand drive models, or behind the right side of the instrument panel on left-hand drive models. On models with the 3S-FE engine the unit is located behind the right side of the instrument panel. On models with an automatic transmission the ECU also controls the transmission.

The ECU receives information from sensors that monitor intake manifold pressure, intake air temperature, coolant temperature, crankshaft speed, throttle valve angle and oxygen content in the exhaust gases. The incoming data is compared with the parameter values stored in the computer memory, and injector control signals are generated on this basis. The injectors are supplied with fuel at constant pressure, determined by the pressure regulator setting; the amount of fuel injected into the cylinders is determined only by the injector opening time.

Under certain conditions the ECU can regulate engine idle speed using an air control valve that opens and closes the bypass passage, directing air around the throttle valve. On models equipped with air conditioning there is an additional valve for regulating idle speed. This device compensates for the power consumed to drive the compressor.

The ECU is equipped with a fail-safe function that allows the vehicle to continue driving, even at reduced power and lower efficiency, if any sensor fails. In this case the warning light on the instrument panel illuminates and the control unit stores a trouble code, which later allows the faulty circuit to be identified. The trouble code can be interpreted at a service station or with the Repair Manual.

Some 4A-FE engines are equipped with the Toyota lean-burn combustion system. On these engines, thanks to the modified intake manifold configuration and fuel injector location, a lean air-fuel mixture can be used without loss of engine output and performance. This system improves fuel economy and significantly reduces exhaust emissions.

The obvious visual difference between engines with conventional and lean-burn combustion is the injector location: in a conventional engine they are located in the intake manifold, whereas in a lean-burn engine they are located in the cylinder head.