Nissan Pick-ups and Pathfinder 1989-1995

General Information

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See Figures 1 through 7

The Nissan Electro Injection System is a throttle body fuel injection system used on 1989 models equipped with the VG30i or Z24i engines. This system is part of Electronic Concentrated Control System (ECCS). The ECCS utilizes a computerized brain center known as the Electronic Control Unit (ECU), along with various sensors and solenoids/regulators to precisely control fuel delivery to the injectors.



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Fig. Fig. 1: Fuel pressure regulator



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Fig. Fig. 2: Fuel injector



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Fig. Fig. 3: Mixture heater



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Fig. Fig. 4: Power transistor and ignition coil



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Fig. Fig. 5: Electronic control unit



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Fig. Fig. 6: Throttle body air flow



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Fig. Fig. 7: Idle speed control device

SYSTEM COMPONENTS



Crank Angle Sensor

The crank angle sensor is a basic component of the entire system. It monitors engine speed/piston position and sends signals which the control unit uses to calculate ignition timing and fuel delivery functions.

The crank angle sensor has a rotor plate and a wave forming circuit. On all models, the signal rotor plate has 360 slits for 1 degree signals (crank angle). On models equipped with VG30i engines, the rotor plate also consists of 6 slits for 120 degree signals (engine speed). On models equipped with Z24i engines, the rotor plate also consists of 4 slits for 180 degree signals (engine speed). 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, causing rough shaped pulses. These pulses are converted into on-off signals by the wave forming circuit and sent to the control unit as input signals.

Air Flow Meter

The air flow meter measures the intake air flow rate by taking a part of the entire flow. Measurements are made in such a manner that the control unit receives electrical output signals which vary by the amount of heat emitted from a hot wire placed in the stream of intake are. When intake are flows into the intake manifold through a route around the hot wire, the heat generated by the wire is taken away by the passing air. The amount of heat removed depends on the air flow, but the maximum temperature of the hot wire is automatically controlled, requiring more electrical current to maintain the controlled temperature in the wire as the amount of intake air increases. By measuring the amount of current necessary to maintain the hot wire temperature, the control unit measures the amount of intake air passing the wire and, therefore, knows the volume of air entering the engine.

Water and Air Temperature Sensors

The water temperature sensor, located on the front side of the intake manifold, detects engine coolant temperature and sends signals to the control unit. The air temperature sensor, installed in the air cleaner, monitors the intake air temperature. Both of these sensors employ a thermistor (temperature dependant resistor) which is sensitive to changes in temperature. The electrical resistance of these thermistors decreases as temperature rises.

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 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.

Throttle Sensor/Idle Switch

The throttle sensor/idle switch is attached to the throttle body and operates in response to accelerator pedal movement. This sensor has 2 functions: it contains an idle switch and throttle position sensor. The idle switch closes when the throttle valve is positioned at idle, and opens when it is in any other position. The throttle sensor is a potentiometer which transforms the throttle valve position into output voltage and feeds the voltage signal to the control unit. In addition, the throttle sensor detects the opening or closing speed of the throttle valve and feeds the rate of voltage change to the control unit.

Power Steering Oil Pressure Switch

A power steering oil pressure switch is attached to the power steering high pressure line and detects the power steering load, sending a load signal to the control unit which then sends the idle-up signal to the Idle Speed Control (ISC) valve.

Fuel Pressure Regulator

A fuel pressure regulator is built into the side of the throttle body. It maintains fuel pressure at a constant value. Since the injected fuel amount depends on injection pulse duration, it is necessary to keep the fuel pressure constant. A fuel pump with a fuel damper is located in the fuel tank. The pump is an electric, vane roller type.

Fuel Injector

The fuel injector is basically a small solenoid valve. The control unit sends electrical signals to the injector in order to actuate a coil which pulls back a ball from the injector check valve. High pressure fuel, which is constantly supplied to the injector (from the fuel pump and lines), then forces past the tiny opening in the nozzle, spraying into the intake. The amount of injected fuel is controlled by the computer through longer or shorter control signals (pulse duration) which simply have the effect of opening the injector valve for a longer or shorter period of time. A mixture heater is located between the throttle valve and the intake manifold. This is designed and operated for atomizing fuel in the cold engine start condition. The heater is also controlled by the computer.

Mixture Heater

The mixture heater is located between the throttle valve and the intake manifold. This is designed and operated for atomizing fuel in the cold engine start condition. The ECU regulates the heater.

Idle Speed Control (ISC) Valve

The Idle Speed Control (ISC) valve is a rotary solenoid valve that receives a pulse signal from the control unit. This pulse signal determines the position of the slider, thereby varying bypass air quantity which raises or lowers the idle speed. The ISC valve has additional functions which include idle-up after cold start (fast idle), idle speed feedback control, idle-up for air conditioner and power steering (fast idle control device) and deceleration vacuum control.

Power Transistor and Ignition Coil

The ignition signal from the ECU is amplified by the power transistor, which turns the ignition coil primary circuit on and off, inducing the proper high voltage in the secondary circuit. The ignition coil is a small, molded type.

Electronic Control Unit (ECU)

In conjunction with its sensors and related components, the ECU basically controls engine operation from ignition to fuel delivery. 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. The unit regulates the ignition timing, idle speed, fuel mixture (based on ratio feedback), fuel pump operation, mixture heating, Air Injection Valve (AIV) operation, Exhaust Gas Recirculation (EGR), and vapor canister purge operation.

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. The fuel is enriched when starting, during warm-up, when accelerating and when operating under a heavy load. The fuel is leaned during deceleration according to the closing rate of the throttle valve.

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 under any of these conditions:



Starting the engine
 
Engine temperature is cold
 
Exhaust gas sensor temperature is cold
 
Driving at high speeds or under heavy load, at idle (after mixture ratio learning is completed)
 
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 battery charging.

The control unit energizes the mixture heating relay when the engine is running and the water temperature is below 122F (50C). The mixture heating relay will be shut off after several minutes when the water temperature exceeds 122F (50C). In addition, the Air Injection Valve (AIV), which supplies secondary air to the exhaust manifold, is controlled by the computer according to engine temperature. When the engine is cold, the AIV system operates to reduce HC and CO emissions. In extremely cold conditions, the AIV control system does not operate to reduce afterburning.

A signal from the control unit is also sent to the EGR and fuel vapor canister purge cut solenoid valve, which cuts the vacuum for the EGR and canister control valve. The EGR and canister purge activates when the vehicle speed is above 6 mph, the water temperature is above 140F (60C) and the engine is under light load or low rpm. The vacuum will be interrupted unless all of the conditions are met.

Finally, the control unit operates the air flow meter self-cleaning system. After the engine is stopped, the control unit heats up the hot wire to approximately 1832F (1000C) to burn off dust adhering to the wire. The self-cleaning function will activate if the engine speed has exceeded 2000 rpm before the key is turned OFF , vehicle speed has exceeded 12 mph before the key is turned OFF , water temperature is 140-203F (60-95C), or the engine has been stopped by turning the ignition key OFF . Self-cleaning will be activated only if all of the above conditions are met. The hot wire will be heated for 0.3 seconds, 5 seconds after the ignition is switched OFF .

There is a fail-safe system built into the control unit should the air flow meter malfunction. If the air flow meter output voltage is higher or lower than the specified value, the control unit senses an air flow meter malfunction and substitutes the throttle sensor signal for the air flow meter input. It is possible to start the engine and drive the vehicle, but the engine speed will not rise more than 2400 rpm, in order to inform the driver of fail-safe system operation while driving.

 
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