Toyota 3S-GE Repair Manual page 178

F
E6464 ENGINE — EFI SYSTEM
The EFI system is composed of three basic sub—systems: Fuel, Air Induction and Electronic
Control Systems.
FUEL SYSTEM
Fuel is supplied under constant pressure to the EFI injectors by an electric fuel pump. The
injectors inject a metered quantity of fuel into the intake manifold in accordance with signals
from the ECU (Engine Control Unit).
AIR INDUCTION SYSTEM
The air induction system provides sufficient air for engine operation.
ELECTRONIC CONTROL SYSTEM
The 3S—GE engine is equipped with a TOYOTA Computer Controlled System (TCCS) which
centrally controls the EFI, ESA, ISC, Diagnosis systems etc. by means of an ECU—formerly EFI
computer employing a microcomputer.
The ECU controls the following functions:
1. Electronic Fuel Injection (EFI)
The ECU receives signals from various sensors indicating changing engine operating conditions
such as:
0 lntake manifold pressure
I lntake air temperature
I Engine coolant temperature
I Engine speed
0 Throttle valve opening angle
I Exhaust oxygen content etc.
The signals are utilized by the ECU to determine the injection duration necessary for an optimum
air—fue| ratio.
2. Electronic Spark Advance (ESA)
The ECU is programmed with data for optimum ignition timing under all operating conditions.
Using data provided by sensors which monitor various engine functions (rpm, coolant tempera-
ture, etc.), the microcomputer (ECU) triggers the spark at precisely the right instant.
3. Idle Speed Control (ISC)
The ECU is programmed with target idling speed values to respond to different engine conditions
(coolant temperature, air conditioning ON/OFF, etc.). Sensors transmit signals to the ECU which
control the flow of air through the throttle valve bypass and adjust idle speed to the target value.
4. Diagnosis
The ECU detects any malfunctions and abnormalities in the sensor network and lights a check
engine warning light in the combination meter. At the same time, trouble is identified and a
diagnostic code is recorded by the ECU. The diagnostic corde can be read by the number of blinks
of the check engine warning light when terminals TE1 and E1 of the check connector are
connected. The diagnistic code are referred to in a later page. (See page EG—-182)
5. Self—Correction Function
If any sensor malfunctions, an average value recorded in the back—up circuit is substituted to
make driving possible. If danger is predicted, the engine is stopped and the check engine warning
light will light up.
6. Fail—Safe Function
In the event of the sensor malfunctioning. a back—up circuit will take over to provide minimal
driveability. and the check engine warning light will illuminate.