Circuit Description

The engine control system utilizes a microcomputer and maintains overall control of the engine, transmission, etc.. an outline of engine control is given here.

1. INPUT SIGNAL
(1) Engine Coolant Temp. (Water Temp.) Signal System
The engine coolant temp. sensor (water temp. sensor) detects the engine coolant temp. and has a built-in thermistor with a resistance which varies according to the engine coolant temp. (water temp). Thus the engine coolant temp. (water temp.) is input in the form of a control signal to TERMINAL THW of the Engine Control Module (engine and electronically controlled transmission ECU (A/T), engine ECU (M/T)).
(2) Intake Air Temp. Signal System
The intake air temp. sensor is installed inside the volume air flow (air flow meter) and detects the intake air temp., which is input as a control signal to TERMINAL THA of the Engine Control Module (ECU).
(3) Oxygen Sensor Signal System
The oxygen density in the exhaust emissions is detected and input as a control signal to TERMINAL OX1 and OX2 of the Engine Control Module (ECU). To maintain stable detection performance by the heated oxygen sensor, a heater is used for warming the sensor. The heater is also controlled by the Engine Control Module (ECU) (ht1.ht2).
(4) RPM Signal System
The crankshaft position and engine speed are detected by the pick-up coil installed inside the distributor,and are input as control signals to TERMINAL NE of the Engine Control Module (ECU).
(5) Throttle Signal System
The throttle position sensor detects the throttle valve opening angle. which is input as a control signal to TERMINAL VTA of the Engine Control Module (ECU), or when the valve is fully closed, to TERMINAL IDL.
(6) Vehicle Speed Signal System
The vehicle speed is detected by vehicle speed sensor (speed sensor) installed in the transmission and the signal is input to TERMINAL SPD of the Engine Control Module (ECU) via the combination meter.
(7) Park/Neutral Position SW (Neutral Start SW) Signal System
The park/Neutral position SW (Neutral start SW) detects whether the shift position is in neutral or not, and inputs a control signal to TERMINAL NSW of the Engine Control Module (ECU).
(8) Battery Signal System
Voltage is constantly applied to TERMINAL BATT of the Engine Control Module (ECU). When the ignition SW is turned to ON, voltage for Engine Control Module (ECU) operation is applied via the EFI main relay to TERMINAL +B of the Engine Control Module (ECU).
(9) Intake Air Volume Signal System
Intake air volume is detected by the potentiometer installed inside the volume air flow (air flow meter) and is input as a control signal to TERMINAL VS of the Engine Control Module (ECU), inside the volume air flow (air flow meter) there is also a SW for fuel pump operation, and when the measuring plate opens (air intake occurs), this SW turns ON and current flows to the fuel pump to operate it.
(10) Stop Light SW Signal System
The stop light SW is used to detect whether or not the vehicle is braking and the information is input as a control signal to TERMINAL STP of the Engine Control Module (ECU).
(11) STA Signal System
To confirm that the engine is cranking, the voltage applied to the starter motor during cranking is detected and is input as a control signal to TERMINAL STA of the Engine Control Module (ECU).
(12) Engine Knock Signal System
Engine knocking is detected by the knock sensor and input as a control signal to TERMINAL KNK of the Engine Control Module (ECU).
(13) 4WD Signal System
Whether or not the vehicle is operating in 4WD mode is determined, and a control signal is input to TERMINAL 4WD of the Engine Control Module (ECU).

2. CONTROL SYSTEM
^ MFI (Multiport Fuel Injection)(EFI) System
The MFI (EFI) system monitors the engine conditions through the signals each sensor (input signals (1 to 11, 13)) inputs to the Engine Control Module (ECU). based on this data and the program memorized in the Engine Control Module (ECU). The most appropriate fuel injection timing is decided and current is output to TERMINALS #10 and #20 of the Engine Control Module (ECU). Causing the injectors to operate it (to inject fuel). It is this system which. through the work of the Engine Control Module (ECU). Finely controls fuel injection in response to driving conditions.
^ ESA (Electronic Spark Advance) system
The ESA system monitors the engine conditions using the signals (input signals(1, 3 to 8, 10, 13) input to the engine control module (ECU) from each sensor. Based on this data and the program memorized in the Engine Control Module (ECU), the most appropriate ignition timing is decided and current is output to TERMINAL IGT of the Engine Control Module (ECU). This output controls the igniter to produce the most appropriate ignition timing for the driving conditions.
^ Fuel Pressure-Up System
The fuel pressure up system causes the VSV (for fuel pressure up) to come on for high temp. starts and for about 120 seconds after starting in order to increase the fuel pressure. improve startability at high temperatures and provide stable idling. the Engine Control Module (ECU) evaluates the input signals from each sensor (1, 2, 4 and 12) outputs current to TERMINAL FPU and controls the VSV.
^ Oxygen Sensor Heater Control System
The oxygen sensor heater control system turns the heater to on when the intake air volume is low (temp. of exhaust emissions low), and warms up the heated oxygen sensor (oxygen sensor) to improve detection performance of the sensor. The Engine Control Module (ECU) evaluates the signals from each sensor (input signals (1, 6, 9, 10, 12)), current is output to TERMINALS HT1 and HT2 and controls the heater.
^ Pair Control System
The pair control system turns ON the VSV (for pair) when the engine is cold and during deceleration, preventing overheating of the TWC (Three-way catalytic converter) and reducing HC and CO emissions. The Engine Control Module (ECU) evaluates the signals from each sensor (input signals (1, 4, 5, 10)), then sends output to TERMINAL AS and controls the VSV.
^ EGR Cut Control System
The EGR cut control system controls the VSV (for EGR) by evaluating the signals from each sensor input to the Engine Control Module (ECU) (input signals (1, 9)) and by sending output to TERMINAL EGR of the Engine Control Module (ECU).

3. DIAGNOSIS SYSTEM
With the diagnosis system, when there is a malfunction in the Engine Control Module (ECU) signal system, the malfunctioning system is recorded in the memory. the malfunctioning system can then be found by reading the display (code) of the malfunction indicator lamp (check engine warning light).

4. FAIL-SAFE SYSTEM
When a malfunction occurs in any system, if there is a possibility of engine trouble being caused by continued control based on the signals from that system, the fail-safe system either controls the system by using data (standard values) recorded in the Engine Control Module (ECU) memory or else stops the engine.