Nissan Pick-ups and Pathfinder 1989-1995

General Information

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The Nissan Electronic Concentrated Control System (ECCS)is an air flow regulated, port fuel injection and engine control system. It is used on 1990-95 models equipped with VG30E and KA24E engines. The KA24E engines use 4 fuel injectors, while the VG30E engines use 6 injectors to spray fuel into the intake manifold near the cylinders' intake valves. The ECCS Electronic Control Unit (ECU) consists of a microcomputer, inspection lamps, a diagnostic mode selector and connectors for signal input and output as well as for power supply. The system's ECU regulates the following functions:



Amount of injected fuel
 
Ignition timing
 
Mixture ratio feedback
 
Pressure regulator control
 
Exhaust Gas Recirculation (EGR) operation
 
Idle speed control
 
Fuel pump operation
 
Air regulator control
 
Air Injection Valve (AIV) operation
 
Self-diagnostics
 
Air flow meter self-cleaning control
 
Fail-safe system
 

SYSTEM COMPONENTS



Crank Angle Sensor

See Figure 1

The crank angle sensor is a basic component of the ECCS system. It monitors engine speed/piston position and sends signals which the ECU uses to regulate 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 degree signals (crank angle). On models equipped with VG30E engines, the rotor plate also consists of 6 slits for 120 degree signals (engine speed). On models equipped with KA24E engines, the rotor plate also consists of 4 slits for 180 degree signals (engine speed).



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Fig. Fig. 1: ECCS distributor with crank angle sensor

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 are then sent to the ECU.

Cylinder Head Temperature Sensor

See Figure 2

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 (temperature variable resistor) which is sensitive to changes in temperature, with electrical resistance decreasing as temperature rises.



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Fig. Fig. 2: Cylinder head temperature sensor

Air Flow Meter

See Figure 3

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, so 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 determines exactly how much air is entering the engine. A self-cleaning system briefly heats the hot air wire to approximately 1832F (1000C) after engine shutdown to burn off any dust or contaminants on the wire.



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Fig. Fig. 3: Air flow meter

Exhaust Gas Sensor

See Figures 4 and 5

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 reads the varying output voltage of the sensor, depending on its resistance. The oxygen sensor is equipped with a heater to bring it to operating temperature quickly.



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Fig. Fig. 4: Exhaust gas sensor-Zirconia tube type



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Fig. Fig. 5: Exhaust gas sensor-Titania type

Throttle Valve Switch

See Figure 6

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.



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Fig. Fig. 6: Throttle valve switch

Fuel Injector

See Figure 7

The fuel injector is a small, precision solenoid valve. As the ECU sends a signal to each injector, the coil built into the injector pulls the needle valve back allowing pressurized fuel to be sprayed through the nozzle and into the intake manifold. The amount of fuel injected is dependent on the length of the signal (pulse duration); the longer the signal, the more fuel delivered.



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Fig. Fig. 7: Fuel injector

Fuel Temperature Sensor

See Figure 8

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.



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Fig. Fig. 8: Fuel temperature sensor

Power Transistor

See Figure 9

The ignition signal from the ECU is amplified by the power transistor, which turns the ignition coil primary circuit on and off, indicating 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.



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Fig. Fig. 9: Power transistor and ignition coil

Vehicle Speed Sensor

See Figure 10

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.



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Fig. Fig. 10: Vehicle speed sensor

Swirl Control Valve (SCV) Control Solenoid Valve

The SCV control solenoid valve cuts the intake manifold vacuum signal for the swirl control valve. It responds to an 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

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 bimetal, heater and rotary shutter are built into the air regulator. When bimetal temperature is low, the air bypass port is open. As the engine starts and electric current flows through a heater, the bimetal begins to rotate the shutter to close off the air bypass port. The air passage remains closed until the engine is stopped and the bimetal temperature drops.

Air Injection Valve (AIV)

Under certain conditions, the Air Injection Valve (AIV) sends secondary air to the exhaust manifold, by utilizing vacuum caused by exhaust pulsation in the exhaust manifold. When exhaust pressure is below atmospheric pressure (negative pressure), secondary air is sent to the exhaust manifold; when 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, and 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.

Exhaust Gas Recirculation (EGR) Vacuum Cut Solenoid 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.

Air Regulator

See Figure 11

The air regulator provides an air bypass when the engine is cold for the purpose of a fast idle during warm-up. A bimetal heater and rotary shutter are built into the air regulator. When the bimetal temperature is low, the air bypass port is open. As the engine starts and electric current flows through a heater, the bimetal begins to rotate the shutter to close off the bypass port. The air passage remains closed until the engine is stopped and the bimetal temperature drops.



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Fig. Fig. 11: Air regulator assembly

Electronic Control Unit (ECU)

See Figure 12

In conjunction with its sensors and related components, the ECU basically regulates the engine. The ECU consists of a microcomputer, inspection lamps, and a diagnostic mode selector, as well as connectors for signal input/output and for power supply.



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Fig. Fig. 12: ECU Control unit

SYSTEM OPERATION



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 (4 injectors on the KA24E engine and 6 injectors on the VG30E engine). The fuel is enriched during starting, warm-up, and acceleration, as well as when cylinder head temperature is high or 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 130 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 that the mixture ratio will be within the narrow window around the stoichiometric fuel ratio. The system goes into closed loop operation as soon as the oxygen sensor heats up enough to register. However, there are several different conditions under which the system will operate in the open loop mode. These include when starting the engine, when the engine temperature is cold, and when the exhaust gas sensor temperature is cold. The system also operates in open loop mode when:



Driving at high speeds or under heavy load, at idle (after mixture ratio learning is completed)
 
During deceleration
 
When the exhaust gas sensor monitors a rich condition for more than 10 seconds.
 
Should the exhaust gas sensor malfunction, the system would also operate in open loop mode.
 

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.

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 68-176F (20-80C). 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.

 
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