Toyota 4A-FE Repair Manual page 79

EFI SYSTEM - System Description
Fl-7
The EFI system is composed of three basic sub-
systems: Fuel. Air Induction and Electronic
Control System.
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
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
4A-FE, 4A-GE 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.
The ECU, the TCCS controls the following func-
tions:
1. Electronic Fuel Injection (EFI)
The ECU receives signals from various sen-
sors indicating changing engine operating
conditions such as:
Intake manifold absolute pressure
(w/o Air flow meter)
Intake air volume
(w/ Air flow meter)
Intake air temperature
Coolant temperature
Engine rpm
Throttle valve opening valve
Exhaust oxygen content (w/ TWC) 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 func-
tions (rpm, coolant temperature, etc.), the
microcomputer (ECU) triggers the spark at
precisely the right instant. (See IG section)
3. Diagnosis
The ECU detects any malfunctions or abnor-
malties in the sensor network and lights
a
"CHECK ENGINE" warning light on the instru-
ment 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 TE1 and E1 are
connected. The diagnostic codes are refered
to the
later
page.
(See pages Fl-28 to 31)
4.
Fail-Safe Function
In the event of the sensor malfanctioning,
a
back-up circuit will take over to provide
minimal driveability, and the "CHECK
ENGINE" warning light will illuminate.