Computers and Control Systems: Description and Operation
MFI System Vacuum And Electrical Schematic:
SYSTEM OUTLINE
The engine control system utilizes an engine control module (ECM) and maintains overall control of engine, emission and transmission functions. An outline of engine control is given here.
INPUT SIGNALS
Engine Coolant Temperature (ECT) Signal System
The engine coolant temperature sensor detects the engine coolant temperature and has a built-in thermistor with a resistance which varies according to the engine coolant temperature Thus the engine coolant temperature is input in the form of a control signal to terminal THW of the ECM.
Intake Air Temperature Signal (IAT) System
The intake air temperature sensor detects the intake air temperature, which is input as a control signal to terminal THA of the ECM.
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.
RPM Signal System
Camshaft position and crankshaft position (engine rpm) are detected by the pick-up coil installed inside the distributor. Camshaft position is input as a control signal to terminals G1 and G- of the ECM, and rpm is input to terminal NE+ and NE-.
Throttle Signal System
The throttle position sensor (TPS) detects the throttle valve opening angle. which is input as a control signal to terminal VTA of the ECM. When the throttle valve is fully closed, a signal is input to terminal IDL.
Vehicle Speed Signal System
The vehicle speed sensor (VSS), installed inside the combination meter, detects the vehicle speed and inputs a control signal to terminal SPD of the ECM.
Park/Neutral Position Switch (PNP) Signal System
The Park/Neutral position switch detects whether the shift position is in neutral or not, and inputs a control signal to terminal NSW of the ECM.
A/C Switch Signal System
The operating voltage of the A/C magnetic clutch is detected and input in the form of a control signal to terminal AC1 of the ECM.
Battery Signal System
Voltage is constantly applied to terminal ACC of the ECM. When the ignition switch is turned to ON, voltage for ECM operation is applied via the EFI main relay to terminal +B of the ECM.
Intake Air Volume Signal System
Intake air volume is detected by the manifold absolute pressure sensor (MAP) and is input as a control signal to terminal PIM of the ECM.
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 ECM.
CONTROL SYSTEM
Multiport Fuel Injection (MFI) System
The MFI system monitors the engine conditions through the signals input from each sensor to the engine control module (ECM). Based on this data and the program memorized in the ECM memory, the most appropriate fuel injection timing is calculated and a ground circuit is provided at terminals #10 and #20 of the ECM, causing the injectors to open and 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, a signal input to terminal STA (or for approx. 2 seconds after an NE signal is input) ECM energizes the fuel pump circuit inside the Circuit Opening Relay, causing the fuel pump to operate.
Electronic Spark Advance (ESA) System
The ESA system monitors the engine conditions using the signals input to the engine control module from each sensor. Based on this data, and the program memorized in the engine control module, the most appropriate ignition timing is calculated and current is output to terminal IGT of the engine control module. This output controls the Igniter to produce the most appropriate ignition timing for the driving conditions.
Idle-up Air Control (ISC) System
The Idle Air Control Valve (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 engine control module evaluates the signals from each sensor, and outputs current to terminal RSC and RSO which 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 engine control module and by sending output to terminal EGR of the engine control module.
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 vehicles throttle valve opening angle and intake manifold pressure in order to maintain acceleration performance. The engine control module receives these signals and outputs signals to terminal ACT.
Emission Controls Operation
The ECM controls the Vacuum Switching Valve for the Evaporative Emissions Control System (VSV for EVAP), which determines when the fuel vapors stored in the charcoal cannister are flushed.
DIAGNOSIS SYSTEM
With the diagnosis system, when there is a malfunction in the engine control module signal system, the malfunction is recorded in the memory. The malfunctioning system can then be found by reading the display code (DTC) of the Malfunction Indicator Lamp ("CHECK" Engine Warning Light).
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 standard data values recorded in the engine control module memory or, in some cases, stops the engine.
ELECTRONICALLY CONTROLLED TRANSMISSION FUNCTIONS
In the case of an automatic transaxle equipped vehicle, the ECM is combined with the transmission control unit into an integral powertrain control module. The transmission control unit employs a separate microprocessor but monitors many of the same input signals that are used by the ECM to control shift timing and Torque Converter lock-up timing. For more information on this function refer to Transmission Control System.
Transmission Control Systems