Toyota 1993 MR2 Wiring Diagrams page 66

ENGINE CONTROL (5S–FE)
SYSTEM OUTLINE
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. PTIS (INPUT SIGNALS)
(1) WATER TEMP. SIGNAL SYSTEM
THE ECTS (WATER TEMP. SENSOR) DETECTS THE ENGINE COOLANT TEMP. AND HAS A BUILT–IN THERMISTOR WITH A
RESISTANCE WHICH VARIES ACCORDING TO THE WATER TEMP. THUS THE WATER TEMP. IS INPUT IN THE FORM OF A
CONTROL SIGNAL TO TERMINAL THW OF THE PCME (ECU).
(2) INTAKE AIR TEMP. SIGNAL SYSTEM
THE IATS (INTAKE AIR TEMP. SENSOR) IS DETECTS THE INTAKE AIR TEMP., WHICH IS INPUT AS A CONTROL SIGNAL TO
TERMINAL THA OF THE PCME (ECU).
(3) OXYGEN DENSITY SIGNAL SYSTEM
THE OXYGEN DENSITY IN THE EXHAUST EMISSIONS IS DETECTED AND INPUT AS A CONTROL SIGNAL TO TERMINAL OX1 AND
OX2 (CALIFORNIA) OF THE PCME (ECU).
(4) CRANKSHAFT POSITION SIGNAL SYSTEM
CRANKSHAFT POSITION AND ENGINE SPEED ARE DETECTED BY THE PICK–UP COIL INSTALLED INSIDE THE DISTRIBUTOR.
CRANKSHAFT POSITION IS INPUT AS A CONTROL SIGNAL TO TERMINAL G+, OF THE PCME (ECU), AND ENGINE SPEED SIGNAL
IS INPUT TO TERMINAL NE+.
(5) THROTTLE POSITION SIGNAL SYSTEM
THE THROTTLE POSITION SENSOR DETECTS THE THROTTLE VALVE OPENING ANGLE, WHICH IS INPUT AS A CONTROL
SIGNAL TO TERMINAL VTA OF THE PCME (ECU), OR WHEN THE VALVE IS FULLY CLOSED, TO TERMINAL IDL.
(6) VEHICLE SPEED SIGNAL SYSTEM
THE SPEED METER INSIDE THE COMBINATION METER SENDS A VEHICLE SPEED SIGNAL TO TERMINAL SPD OF THE PCME
(ECU) AS A CONTROL SIGNAL.
(7) NEUTRAL POSITION SIGNAL SYSTEM (A/T)
THE PNS (NEUTRAL START SW) DETECTS WHETHER THE SHIFT POSITION IS IN NEUTRAL AND PARKING OR NOT, AND INPUTS
A CONTROL SIGNAL TO TERMINAL NSW OF THE PCME (ECU).
(8) A/C SW SIGNAL SYSTEM
THE A/C AMPLIFIER INPUTS THE A/C OPERATIONS TO TARMINAL ACA OF THE PCME (ECU) AS A CONTROL SIGNAL.
(9) BATTERY SIGNAL SYSTEM
VOLTAGE IS CONSTANTLY APPLIED TO TERMINAL BATT OF THE PCME (ECU). WHEN THE IGNITION SW IS TURNED TO ON,
VOLTAGE FOR ECU OPERATION IS APPLIED VIA THE EFI MAIN RELAY TO TERMINALS +B AND +B1 OF THE PCME (ECU).
(10) INTAKE AIR VOLUME SIGNAL SYSTEM
INTAKE AIR VOLUME IS DETECTED BY THE MAP (VACUUM SENSOR) AND IS INPUT AS A CONTROL SIGNAL TO TERMINAL PIM
OF THE PCME (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 PCME (ECU).
(12) ELECTRICAL LOAD SIGNAL SYSTEM
THE SIGNAL WHEN SYSTEMS SUCH AS THE REAR WINDOW DEFOGGER, HEADLIGHTS, ETC. WHICH CAUSE A HIGH
ELECTRICAL BURDEN ARE ON IS INPUT TO TERMINAL ELS AS A CONTROL SIGNAL.
2. CONTROL SYSTEM
* MPI (EFI, ELECTRONIC FUEL INJECTION) SYSTEM
THE MPI (EFI) SYSTEM MONITORS THE ENGINE REVOLUTIONS THROUGH THE SIGNALS EACH SENSOR (INPUT SIGNALS (1) TO
(12)) INPUTS TO THE PCME (ECU). BASED ON THIS DATA AND THE PROGRAM MEMORIZED IN THE PCME (ECU), THE MOST
APPROPRIATE FUEL INJECTION TIMING IS DECIDED AND CURRENT IS OUTPUT TO TERMINALS #10 AND #20 OF THE PCME (ECU),
CAUSING THE INJECTORS TO OPERATE IT (TO INJECT FUEL). IT IS THIS SYSTEM WHICH, THROUGH THE WORK OF THE PCME
(ECU), FINELY CONTROLS FUEL INJECTION IN RESPONSE TO DRIVING CONDITIONS.
DURING ENGINE CRANKING (SIGNAL INPUT TO TERMINAL STA) OR FOR APPLOX. 2 SECONDS AFTER NE SIGNAL INPUT, PCME
(ECU) OPERATION ENERGIZES (POINT CLOSED) THE FUEL PUMP CIRCUIT INSIDE THE CIRCUIT OPENING RELAY, CAUSING THE
FUEL PUMP TO OPERATE.
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