System Outline

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

1. INPUT SIGNALS
1. ENGINE COOLANT TEMP. SIGNAL SYSTEM
The engine coolant temp. sensor detects the engine coolant temp. and has a built-in thermistor with a resistance which varies according to the engine coolant temp. . thus the engine coolant temp. is input in the form of a control signal to TERMINAL THW of the ECM.

2. INTAKE AIR TEMP. SIGNAL SYSTEM
The intake air temp. sensor detects the intake air temp.. which is input as a control signal to TERMINAL THA of the ECM.

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 ECM.

4. RPM SIGNAL SYSTEM
Crankshaft position and engine RPM are detected by the pick-up coil installed inside the distributor. Crankshaft position is input as a control signal to TERMINALS G1 and G- of the ECM, and engine RPM is input to TERMINALS NE+ and NE-.

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 ECM, or when the valve is fully closed, to TERMINAL IDL.

6. VEHICLE SPEED SIGNAL SYSTEM
The vehicle speed sensor (speed sensor) detects the vehicle speed and inputs a control signal to TERMINAL SPD of the ECM 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 ECM.

8. A/C SW SIGNAL SYSTEM
The operating voltage of the A/C magnetic clutch is detected and is input in the form of a control signal to TERMINAL ACT of the ECM and operation A/C Idle-Up VSV is detected and is input in the form of a control signal to TERMINAL AC1 of the ECM.

9. BATTERY SIGNAL SYSTEM
Voltage is constantly applied to TERMINAL BATT of the ECM. When the ignition SW is turned to ON, voltage for ECM operation is applied via the EFI Main relay to TERMINAL +B of the ECM.

10. INTAKE AIR VOLUME SIGNAL SYSTEM
Intake air volume is detected by the manifold absolute pressure sensor (MAP sensor) and is input as a control signal to TERMINAL PIM of the ECM.

11. STA SIGNAL SYSTEM
To confirm that the engine is cranking, voltage applied to the starter motor during cranking is detected and is input as a control signal to TERMINAL STA of the ECM.

12. ELECTRICAL LOAD SIGNAL SYSTEM
The signal, when systems such as the rear window defogger, headlight, etc. which cause a high electrical burden are on, is input to TERMINAL ELS as a control signal.

2. CONTROL SYSTEM
^ MULTIPORT FUEL INJECTION (MFI) SYSTEM
The MFI system monitors the engine conditions through the signals from each sensor {input signals (1) to (12)} input to the ECM based on this data and the program memorized in the ECM, the most appropriate fuel injection timing is decided and current is output to TERMINALS #10 and #20 of the ECM, causing the injectors to inject fuel. It is this system which, through the work of the ECM, finely controls fuel injection in response to driving conditions.
During engine cranking (signal input to TERMINAL STA) or for approx. 2 Seconds after NE signal input, ECM operation energizes (point closed) the fuel pump circuit inside the circuit opening relay, causing the fuel pump to operate.

^ ESA (ELECTRONIC SPARK ADVANCE) SYSTEM
The ESA system monitors the engine conditions using the signals {input signals (1, 2, 3, 4, 5, 9, 10)} input to the ECM from each sensor. Based on this data and the program memorized in the ECM, the most appropriate ignition timing is decided and current is output to TERMINAL IGT of the ECM. This output controls the igniter to produce the most appropriate ignition timing for the driving conditions.

^ IDLE AIR CONTROL (IAC) SYSTEM
The idle air control (IAC) system (Rotary Solenoid type) increases the RPM and provides idling stability for fast idle-up when the engine is cold and when the idle speed has dropped due to electrical load, etc. the ECM evaluates the signals from each sensor {input signals (1, 2, 3, 5, 8, 10 and 12)}, outputs current to TERMINAL RSC and RSO, and controls the idle air control valve (IAC valve).

^ EGR CUT CONTROL SYSTEM
The EGR cut control system controls the VSV (for EGR) by evaluating the signals from each sensor input to the ECM {input signals (1 thru 6 and 10)} and by sending output to TERMINAL EGR of the ECM.

^ A/C CUT CONTROL SYSTEM
When the vehicle suddenly accelerates from low engine speed, this system cuts off air conditioning operation for a fixed period of time in response to the vehicle speed, throttle valve opening angle and intake manifold pressure in order to maintain acceleration performance.
The ECM receives input signals (4, 5, 6 and 8), and outputs signals to TERMINAL ACT.

3. DIAGNOSIS SYSTEM
With the diagnosis system, when there is a malfunctioning in the ECM signal system, the malfunction 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 problems 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 ECM memory or else stops the engine.