The EFI system is composed of 3 basic sub systems: Fuel, Air Induction and Electronic Control Systems. FUEL SYSTEM An electric fuel pump supplies sufficient fuel, under a constant pressure, to the injectors. These injectors inject a measured quantity of fuel into the intake ports in accordance with signals from the ECU (Electronic Control Unit). AIR INDUCTION SYSTEM The air induction system provides sufficient air for engine operation. ELECTRONIC CONTROL SYSTEM The TCCS and 7M-GTE engines are equipped with a Toyota Computer Control System (TCCS) which centrally controls the EFI, ESA, Diagnosis systems, etc. by means of an Electronic Control Unit (ECU formerly EFI Computer) employing a microcomputer. By means of the ECU, the TCCS controls the following functions: 1. Electronic Fuel Injection (EFI) The ECU receives signals from various sensors indicating changing engine operating conditions such as: Intake air oxygen content Intake air volume Intake air temperature Coolant temperature Engine rpm Acceleration/deceleration etc. These signals are utilized by the ECU to determine the injection duration necessary for an optimum air-fuel ratio. 2. Electronic Spark Advance (ESA) The ECU is programmed with data for optimum ignition timing under any and all operating conditions. Using data provided by sensors which monitor various engine functions (rpm, A/C signal, coolant temperature, etc.), the microcomputer (ECU) triggers the spark at precisely the right instant. (See IG section) 3. Idle Speed Control (ISC) The ECU is programmed with target engine speed values to respond to different engine conditions (coolant temperature, air conditioning switch operation, etc.). It then sends signals to the ECU which control the flow of air through the by-pass of the throttle valve and adjust idle speed to the target value. (See pages FI-44, 65, 106) 4. Diagnosis The ECU detects any malfunctions or abnormalities in the sensor network and lights the "CHECK ENGINE" warning lamp on the instrument panel. At the same time, the trouble is identified and a diagnostic code is recorded by the ECU. (See page FI-26) 5. Fail-Safe Function In the event of computer malfunction, a backup circuit will take over to provide minimal drivability. Simultaneously, the "CHECK ENGINE" warning light will come on.