The Nissan Electronic Concentrated Control System (ECCS) is an air flow controlled, port fuel injection and engine control system. The ECCS electronic control unit consists of a microcomputer, inspection lamps, a diagnostic mode selector and connectors for signal input and output and for power supply. The electronic control unit, or ECU, controls the following functions:
Crank Angle Sensor
See Figure 1
The crank angle sensor is a basic component of the ECCS system. It monitors engine speed and piston position, as well as sending signals which the ECU uses to control fuel injection, ignition timing and other functions. The crank angle sensor has a rotor plate and a wave forming circuit. On all models, the rotor plate has 360 slits for 1° signals (crank angle). On models equipped with VG30E engine, the rotor plate also consists of 6 slits for 120° signal (engine speed). On models equipped with CA20E, CA18ET, CA18DE and KA24E engines, the rotor plate also consists of 4 slits for 180° signal (engine speed).
The light emitting diodes (LED's) and photo diodes are built into the wave forming circuit. When the rotor plate passes the space between the LED and the photo diode, the slits of the rotor plate continually cut the light which is sent to the photo diode from the LED. This generates rough shaped pulses which are converted into ON/OFF pulses by the wave forming circuit and then sent to the ECU.
See Figure 2, 3, 4, 5 and 6
The cylinder head temperature sensor monitors changes in cylinder head temperature and transmits a signal to the ECU. The temperature sensing unit employs a thermistor which is sensitive to the change in temperature, with electrical resistance decreasing as temperature rises.
The air flow meter measures the mass flow rate of intake air. The volume of air entering the engine is measured by the use of a hot wire placed in the intake air stream. The control unit sends current to the wire to maintain it at a preset temperature. As the intake air moves past the wire, it removes heat and the control unit must increase the voltage to the wire to maintain it at the preset temperature. By measuring the amount of current necessary to maintain the temperature of the wire in the air stream, the ECU knows exactly how much air is entering the engine. A self-cleaning system briefly heats the hot air wire to approximately 1832°F (1000°C) after engine shutdown to burn off any dust or contaminants on the wire.Exhaust Gas Sensor
The exhaust gas sensor, which is placed in the exhaust pipe, monitors the amount of oxygen in the exhaust gas. The sensor is made of ceramic titania which changes electrical resistance at the ideal air/fuel ratio (14.7:1). The control unit supplies the sensor with approximately 1 volt and takes the output voltage of the sensor depending on its resistance. The oxygen sensor is equipped with a heater to bring it to operating temperature quickly.Throttle Valve Switch
See Figure 7
A throttle valve switch is attached to the throttle chamber and operates in response to accelerator pedal movement. The switch has an idle contact and a full throttle contact. The idle contact closes when the throttle valve is positioned at idle and opens when it is in any other position.
See Figure 8
The fuel injector is a small, precision solenoid valve. As the ECU sends an injection signal to each injector, the coil built into the injector pulls the needle valve back and fuel is injected through the nozzle and into the intake manifold. The amount of fuel injected is dependent on how long the signal is (pulse duration); the longer the signal, the more fuel delivered.
See Figure 9
The detonation sensor is attached to the cylinder block and senses engine knocking conditions. A knocking vibration from the cylinder block is applied as pressure to the piezoelectric element. This vibrational pressure is then converted into a voltage signal which is delivered as output.
See Figure 10, 11, 12
A fuel temperature sensor is built into the fuel pressure regulator. When the fuel temperature is higher than the preprogrammed level, the ECU will enrich the fuel injected to compensate for temperature expansion. The temperature sensor and pressure regulator should be replaced as an assembly if either malfunctions. The electric fuel pump with an integral damper is installed in the fuel tank. It is a vane roller type with the electric motor cooled by the fuel itself. The fuel filter is of metal construction in order to withstand the high fuel system pressure. The fuel pump develops 61-71 psi, but the pressure regulator keeps system pressure at 36 psi in operation.
The ignition signal from the ECU is amplified by the power transistor, which turns the ignition coil primary circuit on and off, inducing the necessary high voltage in the secondary circuit to fire the spark plugs. Ignition timing is controlled according to engine operating conditions, with the optimum timing advance for each driving condition preprogrammed into the ECU memory.Vehicle Speed Sensor
See Figure 13
The vehicle speed sensor provides a vehicle speed signal to the ECU. On conventional speedometers, the speed sensor consists of a reed switch which transforms vehicle speed into a pulse signal. On digital electronic speedometers, the speed sensor consists of an LED, photo diode, shutter and wave forming circuit. It operates on the same principle as the crank angle sensor.
The SCV control solenoid valve cuts the intake manifold vacuum signal for the swirl control valve. It responds to ON/OFF signal from the ECU. When the solenoid is off, the vacuum signal from the intake manifold is cut. When the control unit sends an ON signal, the coil pulls the plunger and feeds the vacuum signal to the swirl control valve actuator.Idle-Up Solenoid Valve
See Figure 14
An idle-up solenoid valve is attached to the intake collector to stabilize idle speed when the engine load is heavy because of electrical load, power steering load, etc. An air regulator provides an air bypass when the engine is cold in order to increase idle speed during warm-up (fast idle). A bi-metal, heater and rotary shutter are built into the air regulator. When bi-metal temperature is low, the air bypass port is open. As the engine starts and electric current flows through a heater, the bi-metal begins to rotate the shutter to close off the air bypass port. The air passage remains closed until the engine is stopped and the bi-metal temperature drops.
See Figure 15
The Air Injection Valve (AIV) sends secondary air to the exhaust manifold, utilizing a vacuum caused by exhaust pulsation in the exhaust manifold. When the exhaust pressure is below atmospheric pressure (negative pressure), secondary air is sent to the exhaust manifold. When the exhaust pressure is above atmospheric pressure, the reed valves prevent secondary air from being sent to the air cleaner. The AIV control solenoid valve cuts the intake manifold vacuum signal for AIV control. The solenoid valve actuates in response to the ON/OFF signal from the ECU. When the solenoid is off, the vacuum signal from the intake manifold is cut. As the control unit outputs an on signal, the coil pulls the plunger downward and feeds the vacuum signal to the AIV control valve.
The EGR vacuum cut solenoid valve is the same type as that of the AIV. The EGR system is controlled by the ECU; at both low and high engine speed (rpm), the solenoid valve turns on and the EGR valve cuts the exhaust gas recirculation into the intake manifold. The pressure regulator control solenoid valve also actuates in response to the ON/OFF signal from the ECU. When it is off, a vacuum signal from the intake manifold is fed into the pressure regulator. As the control unit outputs an on signal, the coil pulls the plunger downward and cuts the vacuum signal.Electronic Control Unit (ECU)
See Figure 16
The ECU consists of a microcomputer, inspection lamps, a diagnostic mode selector, and connectors for signal input and output, and for power supply. The unit has control of the engine.
See Figure 17
The air regulator provides an air bypass when the engine is cold for the purpose of a fast idle during warm-up. A bi-metal, heater and rotary shutter are built into the air regulator. When the bi-metal temperature is low, the air bypass port is open. As the engine starts and electric current flows through a heater, the bi-metal begins to rotate the shutter to close off the bypass port. The air passage remains closed until the engine is stopped and the bi-metal temperature drops.
The IAA consists of the AAC valve, FICD solenoid valve and an idle adjust screw. It receives signals from the ECU and controls the idle speed to the pre-set valve.
The FICD solenoid valve compensates for change in the idle speed caused by the operation of the air compressor. A vacuum control valve is installed in this unit to prevent an abnormal rise in the intake manifold vacuum pressure during decelerationAuxiliary Air Control (AAC) Valve
See Figure 18
The AAC valve is attached to the intake collector. The ECU actuates the AAC valve by an ON/OFF pulse of approximately 160 Hz. The longer that ON duty is left on, the larger the amount of air that will flow through the AAC valve.
In operation, the on-board computer (control unit) calculates the basic injection pulse width by processing signals from the crank angle sensor and air flow meter. Receiving signals from each sensor which detects various engine operating conditions, the computer adds various enrichments (which are preprogrammed) to the basic injection amount. In this manner, the optimum amount of fuel is delivered through the injectors. The fuel is enriched when starting, during warm-up, when accelerating, when cylinder head temperature is high and when operating under a heavy load. The fuel is leaned during deceleration according to the closing rate of the throttle valve. Fuel shut-off is accomplished during deceleration, when vehicle speed exceeds 137 mph, or when engine speed exceeds 6400 rpm for about 500 revolutions.
The mixture ratio feedback system (closed loop control) is designed to control the air/fuel mixture precisely to the stoichiometric or optimum point so that the 3-way catalytic converter can minimize CO, HC and NOx emissions simultaneously. The optimum air/fuel fuel mixture is 14.7:1. This system uses an exhaust gas (oxygen) sensor located in the exhaust manifold to give an indication of whether the fuel mixture is richer or leaner than the stoichiometric point. The control unit adjusts the injection pulse width according to the sensor voltage so the mixture ratio will be within the narrow window around the stoichiometric fuel ratio. The system goes into closed loop as soon as the oxygen sensor heats up enough to register. The system will operate under open loop when starting the engine, when the engine temperature is cold, when exhaust gas sensor temperature is cold, when driving at high speeds or under heavy load, at idle (after mixture ratio learning is completed), during deceleration, if the exhaust gas sensor malfunctions, or when the exhaust gas sensor monitors a rich condition for more than 10 seconds and during deceleration.
Ignition timing is controlled in response to engine operating conditions. The optimum ignition timing in each driving condition is preprogrammed in the computer. The signal from the control unit is transmitted to the power transistor and controls ignition timing. The idle speed is also controlled according to engine operating conditions, temperature and gear position. On manual transmission models, if battery voltage is less than 12 volts for a few seconds, a higher idle speed will be maintained by the control unit to improve charging function.
There is a fail-safe system built into the ECCS control unit. If the output voltage of the air flow meter is extremely low, the ECU will substitute a preprogrammed value for the air flow meter signal and allow the vehicle to be driven as long as the engine speed is kept below 2000 rpm. If the cylinder head temperature sensor circuit is open, the control unit clamps the warm-up enrichment at a certain amount. This amount is almost the same as that when the cylinder head temperature is between 68-176°F (20-80°C). If the fuel pump circuit malfunctions, the fuel pump relay comes on until the engine stops. This allows the fuel pump to receive power from the relay.