System Description - Toyota 4-Runner 1985 Repair Manual

EFI SYSTEM - System Description
FI-3
By means of the ECU, the TCCS controls the fol-
lowing functions:
Electronic Fuel Injection (EFI)
The ECU receives signals from various sensors
indicating changing engine operation condi-
tions such as:
Intake air volume
Intake air temperature
Coolant temperature
Engine rpm
Acceleration/deceleration
Exhaust Ox content etc.
These signals are uti lized by the ECU to deter-
mine the injection duration necessary for an
optimum air-fuel ratio.
2. Electronic Spark Advance (ESA)
The ECU is programmed with data for opti-
mum ignition timing under any and all
operating conditions. Using data provided by
sensors which monitor various engine func-
tions (rpm, intake air volume coolant temper-
ature, etc.), the microcomputer (ECU) trig-
gers the spark at precisely the right instant.
(See IG section)
3. Diagnostics
The ECU detects any malfunctions or abnor-
malities in the sensor network and lights a
"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. There are 12 different
diagnostic codes, including "normal opera-
tion" and these can be confirmed by use of an
analog voltmeter.
(See page F 1-22)
4. Fail-Safe Function
In the event of ECU malfunction, a back-up
circuit will take over to provide minimal
drivability. Simultaneously, the "CHECK
ENGINE" warning light is activated.