Computers and Control Systems: Description and Operation

EFI / TCCS SYSTEM DESCRIPTION
The EFI used on Toyotas has three basic systems.

FUEL SYSTEM
An electric fuel pump supplies sufficient fuel, under a constant pressure, to the EFI injectors.

These injectors inject a metered quantity of fuel into the intake manifold in accordance with signals from the ECU. Each injector injects, at the same time, one half of the fuel required for ideal combustion with each engine revolution.

AIR INDUCTION SYSTEM
The air induction system provides sufficient air for engine operation.

ELECTRONIC CONTROL SYSTEM
The 3VZ-E engine is 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 operation conditions such as:
^ Intake air volume
^ Intake air temperature
^ Coolant temperature
^ Engine rpm
^ Acceleration/deceleration
^ Exhaust oxygen content 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, intake air volume, coolant temperature, etc.), the microcomputer (ECU) triggers the spark at precisely the right instant.

3. Electronic Controlled Transmission (ECT)
The ECU signals the ECT ECU, which outputs the throttle opening angle signal and the coolant temperature condition signal to control the torque converter lock-up.

4. Diagnosis
The ECU detects any malfunctions or abnormalties in the sensor network and lights the "CHECK ENGINE" warning light on the instrument panel. At the same time, the trouble is identified and a diagnostic code is recorded by the ECU. The diagnostic code can be read by the number of blinks of the "CHECK ENGINE" warning light when terminals T and E1 are short-circuited. There are 18 (Federal and Canada), 19 (California) different diagnostic codes including one for "normal operation."

5. Fail-Safe
In the event of a sensor malfunction, a backup circuit will take over to provide minimal driveablity, and the "CHECK ENGINE" warning light will light.