Fuel Injection System - Bosch Afc Nissan Pulsar N13

EFI SYSTEM DESCRIPTION

Note. For specifications on Throttle Position Sensor (TPS), idle speed and mixture, and fuel pump output volume, refer to the appropriate article in the TUNE-UP or ENGINE PERFORMANCE Section.

The Bosch AFC (L-Jetronic) fuel injection system is used on all models. However, variations may exist between model applications. For computer control information, see the appropriate article in the COMPUTER ENG CONTROL or ENGINE PERFORMANCE Section.

The Bosch Airflow Controlled (AFC) fuel injection system is an electronically controlled system operated by incoming airflow. The AFC fuel injection system also contains a feedback system which measures oxygen content of exhaust gases and maintains the air/fuel ratio at about 14.7:1.

The fuel injection system consists of an electric fuel pump, fuel pressure regulator, fuel damper, fuel injectors, Electronic Control Unit (ECU), and airflow meter. In addition, an air temperature sensor, throttle position sensor, coolant temperature sensor, oxygen sensor, catalytic converter, auxiliary air valve, idle speed control valve, throttle body, and electrical relays are used.

Note. Not all models use all components.

ELECTRIC FUEL PUMP(S)

Fuel under pressure from electric fuel pump flows through a fuel damper, fuel filter, injector fuel rail and fuel pressure regulator. Fuel pump(s) may be located on frame rail, in fuel tank or both. Electrical power for fuel pump operation during cranking mode is provided from starter relay via the fuel pump relay (if equipped) and ECU.

At idle, the airflow meter measuring flap opens slightly (about 5 degrees). This action closes the fuel pump contacts and provides power to fuel pump after engine has started.

With engine stopped, no airflow is present, measuring flap closes and fuel pump contacts are opened to cut power to fuel pump. This reduces the risk of fire, in case of collision.

FUEL PRESSURE REGULATOR

The pressure regulator is a sealed unit which is divided by a diaphragm into 2 chambers (fuel and spring chambers). The fuel chamber receives fuel through the inlet side from injector fuel rail. The spring chamber is connected to intake manifold vacuum.

At idle, intake manifold vacuum is high. The diaphragm is pulled down by intake manifold vacuum. Any excessive fuel is returned to the fuel tank. As the throttle is depressed, intake manifold vacuum decreases. The regulator increases fuel pressure to maintain the same fuel pressure-to-intake manifold vacuum difference as during high intake manifold vacuum.

On all except Stanza, a fuel temperature sensor is built into the pressure regulator to improve hot engine start-up. See PRESSURE REGULATOR CONTROL UNIT under SPECIAL FEATURES.

FUEL INJECTORS

A fuel rail links the fuel pressure regulator with the fuel injectors. Each cylinder is provided with a solenoid-operated injector which sprays fuel toward the back of each intake valve.

Injectors are energized by the battery through a fusible link. All models are grounded through the ECU. The injectors on some models are linked to resistors to reduce operating voltage to 3 volts and to protect injectors from power surges.

The ECU controls the injectors and the length of time they are open. The "open" time of the injector governs the amount of fuel delivered. The injectors deliver 1/2 the amount of fuel required once every crankshaft revolution.

ELECTRONIC CONTROL UNIT (ECU) OPERATION

All components of the control system are electrically connected to the ECU. (Scheme 72) The ECU is a pre-programmed computer which receives and interprets data from various sensors to calculate the amount of fuel required by the engine to maintain efficiency with minimum exhaust emissions. The oxygen sensor informs the ECU of oxygen content of exhaust gases and the ECU constantly adjusts the air/fuel ratio by controlling the injector "on" time.

An automatic function of the ECU is to provide fuel enrichment whenever engine is cranked, regardless of engine temperature. This is activated by a direct electrical connection from the starter circuit to the ECU (most models). The ECU is a sealed unit, and no service is required.

Electronic Control Unit (ECU). Scheme 72

Maxima & 300ZX

Airflow meter measures the mass flow rate of the incoming air. It then sends an output signal to the ECU, where output is converted into an intake air signal (engine load).

Air flowing around the hot wire removes heat. Temperature of the hot wire is very sensitive to the mass flow rate of air. The higher the temperature of the hot wire, the higher its resistance value. The change in temperature, or resistance, is determined by the mass flow of air.

After the engine is turned off, the ECU heats up the hot wire to approximately 1832°F (1000°C) to burn off dust which adheres to hot wire during vehicle operation. The self-cleaning operation occurs only if the engine is operated above 1500 RPM, after driving vehicle at 12 MPH or higher, and when cylinder head temperature is less than 239°F (115°C).

All Other Models

Airflow meter measures the amount of air aspirated and provides a signal to the control unit. The aspirated air applies force to the flap so that its opening angle is balanced with the return torque of the helical spring. The flap shaft is connected to a potentiometer, which corresponding with its opening angle, provides a voltage signal to the control unit.

After engine start-up, a set of contacts are closed to signal fuel pump operation. (Scheme 73)

Bosch AFC Airflow Meter (Except Hot-Wire Type). Scheme 73

AIR TEMPERATURE SENSOR

The air temperature sensor is an integral component of the airflow meter which converts temperature of incoming air into electrical signals. These signals are received by the ECU and processed to adjust the amount of fuel delivered by the injectors. The air temperature sensor is not serviceable.

THROTTLE POSITION SENSOR (TPS)

A contact-type TPS is installed on the throttle chamber. It converts throttle position into electrical signals to inform ECU of throttle position. Signals are sent to ECU when throttle is fully open or at idle. (Scheme 74) Some models send a specific signal to ECU, depending on throttle angle. The open contacts prevent loss of power during sudden acceleration/deceleration by signaling ECU of the required fuel enrichment.

Typical Contact-Type Throttle Position Sensor. Scheme 74

COOLANT TEMPERATURE SENSOR

This sensor provides ECU with engine temperature information relating to warm-up enrichment operation. Some models use a dual-sensor element which also signals the ignition computer (if equipped).

During warm-up period after a cold engine start, additional fuel is required to maintain engine performance. As engine temperature increases, the ECU decreases fuel enrichment until engine reaches normal operating temperature.

ELECTRICAL RELAYS

The various relays used with the electronic controls of the AFC injection system control power to injectors, fuel pump, ECU, and cold start system. The electrical relays may consist of one component for all relays or a combination of individual relays.

AUXILIARY AIR VALVE

Most models with Bosch AFC fuel injection use an Auxiliary Air Valve (AAV) to shorten engine warm-up time. The AAV supplies additional air into the intake system which increases engine RPM during a cold start.

The AAV consists of an electrically heated bi-metallic strip, movable disc, and air by-pass channel. The heater coil on the bi-metallic strip is energized by the fuel pump relay. Control of the valve is based upon engine temperature; the air by-pass channel is open when engine is cold and gradually closes as temperature rises. At predetermined temperatures, air by-pass channel is blocked and additional airflow stops. (Scheme 75)

Typical Auxiliary Air Valve. Scheme 75

COLD START INJECTOR

A cold start injector is not used on these models. Additional fuel for cold engine operation is provided by the fuel injectors.

IDLE ADJUSTMENTS

For idle adjustments, see appropriate article in the TUNE-UP or ENGINE PERFORMANCE Section.

THROTTLE POSITION SENSOR

For diagnosis & testing, see ECC CEC SYSTEM article in the COMPUTER ENG CONTROL or ENGINE PERFORMANCE Section.

TESTING

Note. For testing of fuel system components not covered in this article, refer to appropriate article in the COMPUTER ENG CONTROL or ENGINE PERFORMANCE Section.

ELECTRONIC CONTROL UNIT (ECU)

Do not attempt to test ECU, as permanent damage could result. It is possible to check wires for continuity. The ECU should only by judged faulty after compression is checked, ignition system has been tested and found problem-free, and all other fuel injection components have been thoroughly tested (including wiring).

Note. AFC electrical systems can be checked by using Electronic Fuel Injection testers prescribed by the manufacturer. Instructions for use of testers must be followed carefully to prevent damage to system.

FUEL INJECTORS & RESISTORS

1. Connect tachometer to engine. Start engine and run at idle. Remove harness connector from injectors one at a time. Engine idle speed should drop 100-300 RPM as each injector is disconnected. If engine idle speed does not drop, check the wiring connector, injector resistance or injection signal from the computer.
2. Disconnect electrical connector from each injector. Measure injector resistance. Resistance should be about 1.5 ohms. If injector is not to specification, replace injector.

FUEL PRESSURE

1. To release fuel system pressure on 300ZX and 300ZX Turbo models, start engine and unplug Blue fuel pump electrical connector in luggage compartment. On 200SX and 200SX Turbo models, unplug fuel pump connector in right rear tool box. After engine stalls, crank engine 2 or 3 times. Turn ignition off. Connect fuel pump electrical connector.
2. On Maxima models, start engine and disconnect fuel pump relay. Fuel pump relay is located on the right front fender. After engine stalls, crank engine 2 or 3 times. Turn ignition off. Connect No. 2 fuel pump relay.
3. Remove fuel filter-to-fuel rail hose and connect a pressure gauge using a "T" fitting. Start engine and read fuel pressure at idle. If pressure is not as specified, replace pressure regulator and repeat test.
4. Disconnect vacuum line from fuel pressure regulator and connect a hand vacuum pump. On 200SX and 300ZX Turbo models, disconnect the fuel pump connector and apply battery power. On Maxima models, remove fuel pump relay and place jumper wire between Light Green/Red and Black/White wires in harness connector. Turn ignition on.
5. On all models, as vacuum is applied to pressure regulator, pressure reading should decrease. See FUEL PRESSURE SPECIFICATIONS table. If pressure and vacuum readings do not conform to specifications, replace fuel pressure regulator.

FUEL PRESSURE SPECIFICATIONS

FUEL PUMP CIRCUIT

For diagnosis & testing, see ECC CEC SYSTEM article in the COMPUTER ENG CONTROL or ENGINE PERFORMANCE Section.

AIR TEMPERATURE SENSOR TEST

For diagnosis & testing, see ECC CEC SYSTEM article in the COMPUTER ENG CONTROL or ENGINE PERFORMANCE Section.

AIRFLOW METER TEST

For diagnosis & testing, see ECC CEC SYSTEM article in the COMPUTER ENG CONTROL or ENGINE PERFORMANCE Section.

AUXILIARY AIR VALVE TEST

Ensure engine is cold, then start engine. Pinch rubber hose between air valve and throttle chamber. Engine speed should decrease. After engine reaches operating temperature, pinch hose again. Engine speed should not decrease more than 50 RPM. If valve does not operate as outlined, replace auxiliary air valve.

ALTITUDE COMPENSATOR SENSOR

For diagnosis & testing, see ECC CEC SYSTEM article in the COMPUTER ENG CONTROL or ENGINE PERFORMANCE Section.

IDLE SPEED CONTROLLER (ISC) VALVE

For diagnosis & testing, see ECC CEC SYSTEM article in the COMPUTER ENG CONTROL or ENGINE PERFORMANCE Section.

Maxima, Stanza, 200SX & 300ZX

This system is used to improve starting of a hot engine. It achieves this by cutting off the intake manifold vacuum signal to the pressure regulator. this system operates only when fuel temperature is above 172°F (78°C), during starting and the first 3 minutes of engine operation, and when the exhaust gas sensor heater is on.

Maxima, 200SX Turbo & 300ZX

Located inside the distributor, the crank angle sensor is a basic signal sensor for the entire Electronic Concentrated Engine Control System (ECCS). It monitors engine speed and piston position. It sends and electrical signal to the ECCS control unit for control of fuel injection, ignition timing, idle speed, fuel pump operation and EGR system operation.

300ZX Turbo

The AAC valve is mounted to the intake collector. Operation is controlled by the ECCS control unit by an "ON/OFF" pulse. The longer that "ON" duty is left on, the greater amount of air will flow through the valve.

The idle-up solenoid valve is mounted to the intake collector. The solenoid valve actuates to stabilize idle speed when engine is under heavy load such as headlamps on, cooling fan on, power steering pump load or when battery voltage is below 12 volts.

Maxima & Stanza

The Air Injection Valve (AIV) sends secondary air to the exhaust manifold, using vacuum caused by exhaust pulsations in the exhaust manifold. Reed valves prevent secondary air from being sent back to the air cleaner. It is controlled by a solenoid valve which is energized by the ECCS control unit.

REMOVAL & INSTALLATION

Disconnect negative battery cable. Clear area to access to ECU. Disconnect electrical connector lock lever (if used) and carefully remove connector. Remove ECU retaining screws and remove ECU. To install, reverse removal procedures.

Disconnect negative battery cable. Disconnect air ducts and hoses connecting air cleaner and airflow meter. Remove air cleaner cover, if required. Remove air flow meter retaining bolts. Unplug airflow meter electrical connector and remove airflow meter. To install, reverse removal procedures.

1. Disconnect negative battery cable. Unplug TPS electrical connector. Remove 2 screws securing TPS to housing. Remove by slowly pulling sensor off throttle shaft.
2. To install, reverse removal procedure. Make sure sensor is aligned on throttle shaft and after replacement, perform TPS adjustment.

Disconnect negative battery cable and remove electrical connector from air valve. Drain engine coolant, if required. Remove air hoses and coolant hoses (if equipped). Remove retaining bolts and remove air valve. To install, reverse removal procedure.

Note. Replacement of temperature sensor requires immediate replacement be available or cooling system be drained below level of sensor.

Disconnect negative battery cable and remove electrical connector from coolant sensor. Drain engine coolant, if required. Remove sensor. To install, reverse removal procedure.

THERMO TIME SWITCH

Note. Thermo time switch removal should be done only when engine is cold. Removal of switch requires having replacement switch ready for immediate installation or cooling system be drained below level of switch.

Disconnect negative battery cable and electrical connector from switch. Drain cooling system as required. Remove switch. To install, reverse removal procedure.

Disconnect negative battery cable and relieve fuel system pressure. Disconnect fuel lines and vacuum line at regulator. Remove pressure regulator. To install, reverse removal procedure.

Removal

1. Release fuel system pressure and disconnect negative battery cable. Unplug electrical connectors from cold start injector and fuel injectors. Disconnect fuel injection wiring harness from clip on fuel rail.
2. Clear fuel rail and injectors by disconnecting all air, vacuum, fuel supply, and fuel return lines. Remove cold start injector fuel rail and fuel injector retaining bolts.
3. Remove fuel rail, cold start injector and fuel injectors as an assembly. Remove fuel supply hose retaining clip from cold start injector and each fuel injector. Remove injectors.
4. To replace injector fuel supply hose, cut hose with soldering iron just enough to remove hose. Do not touch any part of injector with soldering iron. Do not mount injector in vise.

Installation

To install, reverse removal procedure. Coat inside of new fuel hose with gasoline and slide onto injector.

Maxima ECCS Wiring Diagram. Scheme 76

Stanza ECCS Wiring Diagram. Scheme 77

Stanza Wagon ECCS Wiring Diagram. Scheme 78

200SX SE ECCS Wiring Diagram. Scheme 79

200SX XE ECCS Wiring Diagram. Scheme 80

300ZX & 300ZX Turbo ECCS Wiring Diagram. Scheme 81