Fuel Injection System - Bosch Afc Nissan 300ZX Z31

DESCRIPTION

Note. The Bosch AFC (L-Jetronic) Fuel Injection system is used on all models; however, variations may exist between model applications. This article covers the Bosch AFC system in general, with manufacturers' differences noted under SPECIAL FEATURES .

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. Only primary sub-systems which affect fuel system operation will be covered in this article. For further information, see TUNE-UP - V6 .

ELECTRIC FUEL PUMP

Fuel under pressure from electric fuel pump flows through a fuel damper, fuel filter, injector fuel rail and fuel pressure regulator. Electrical power for fuel pump operation during cranking mode is provided from starter relay via the fuel pump relay and ECU.

At idle, the airflow meter measuring flap opens slightly (about 5°) which 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 method reduces the risk of fire, in case of a 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 the injector fuel rail. The spring chamber is connected to intake manifold vacuum.

At idle, when fuel requirements are low, the diaphragm is pulled down by intake manifold vacuum to allow excessive fuel to return to the fuel tank. As the throttle is depressed and fuel requirements increase, intake manifold vacuum decreases and diaphragm moves up shutting off the fuel return line to maintain constant fuel pressure.

A fuel temperature sensor is built into the pressure regulator to improve the hot engine start-up. Refer to the PRESSURE REGULATOR CONTROL UNIT in SPECIAL FEATURES section.

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 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)

All components of the control system are electrically connected to the ECU. (Scheme 44) 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 "open" 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 44

AIRFLOW METER

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 flowrate 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 flowrate 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).

Bosch AFC Airflow Meter. Scheme 45

THROTTLE BODY

The throttle body controls the intake airflow in response to accelerator pedal movement. Located between the airflow meter and the intake manifold, the throttle body shaft is connected to throttle position sensor.

Most models have a dashpot mounted on the throttle body. The dashpot is used to decrease the intake air gradually when throttle valve is closed.

Note. Many models are equipped with a dashpot to prevent abrupt closing of throttle valve during deceleration and shifting.

THROTTLE POSITION SENSOR

A contact-type throttle position sensor is installed on the throttle chamber of all models. 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 46) The potentiometer prevents loss of power during sudden acceleration/ deceleration by signaling the ECU of necessary fuel enrichment requirements.

Contact-Type Throttle Position Sensor. Scheme 46

COOLANT TEMPERATURE SENSOR

This sensor provides ECU with engine temperature information relating to warm-up enrichment operation. 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 auxiliary air valve supplies additional air into the intake system which increases engine RPM during a cold start.

The auxiliary air valve 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 47)

Auxiliary Air Valve. Scheme 47

COLD START INJECTOR

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

IDLE ADJUSTMENTS

See TUNE-UP - V6 .

For more detailed information, see ECC CEC SYSTEM .

TESTING

Note. For more detailed information, see ECC CEC SYSTEM

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.

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 or injection signal from the computer.

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.
2. 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.
3. Disconnect vacuum line from fuel pressure regulator and connect a hand vacuum pump. On Turbo models, disconnect the fuel pump connector and apply battery power.
4. As vacuum is applied to pressure regulator, pressure reading should decrease. See «FUEL PRESSURE SPECIFICATIONS»(/nissan/300zx/z31-1983-1989/remont/testing-diagnostics/#fuel-injection-system-bosch-afc) table. If pressure and vacuum readings do not conform to specifications, replace fuel pressure regulator.

FUEL PRESSURE SPECIFICATIONS

FUEL PUMP CIRCUIT

For more detailed information, see ECC CEC SYSTEM .

AIR TEMPERATURE SENSOR

For more detailed information, see ECC CEC SYSTEM .

AIRFLOW METER POTENTIOMETER

For more detailed information, see ECC CEC SYSTEM .

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.

Note. To avoid damage to injector, perform this test within the shortest possible time.

1. Disconnect negative battery cable, and cold start injector connector. Remove cold start injector (with fuel supply connected) and place over glass container.
2. Connect battery power to injector terminals. Fuel should spray from injector. If not, replace cold start injector.
3. Disconnect test harness from cold start injector and check for fuel leakage from injector. Maximum leakage is less than one drop of fuel per minute. Resistance between cold start injector terminals should be 3-5 ohms.

1. Warm engine to normal operating temperature and stop engine. Using a thermometer, measure temperature of coolant. Disconnect negative battery cable and sensor electrical connector.
2. Connect ohmmeter leads to both terminals of sensor. Readings should be as specified for corresponding temperatures. See «COOLANT TEMPERATURE SENSOR RESISTANCE»(/nissan/300zx/z31-1983-1989/remont/testing-diagnostics/#fuel-injection-system-bosch-afc) table. If not, replace coolant temperature sensor.

COOLANT TEMPERATURE SENSOR RESISTANCE

PRESSURE REGULATOR CONTROL UNIT

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.

CRANK ANGLE SENSOR

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

Turbo Models

The A.A.C. valve is mounted to the intake collector. Operation is controlled by the E.C.C.S. 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.

IDLE-UP SOLENOID 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.

AIR REGULATOR

The air regulator allows air to by-pass to the intake manifold when engine is cold for the purpose of a fast idle during warm-up. A bi-metallic sensor, heater and rotary shutter are built into the regulator. When bi-metallic sensor temperature is low, the air by-pass port is open. As the engine warms up and electric current runs through the heating element, bimetal sensor begins to rotate the shutter closing off the air by-pass port.

* PLEASE READ FIRST *

Removal & Installation

Disconnect negative battery cable. Clear area for 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 procedure.

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

1. Disconnect negative battery cable. Unplug throttle position sensor electrical connector. Remove 2 screws securing throttle position sensor 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 throttle position sensor adjustment. See «ADJUSTMENTS»(/nissan/300zx/z31-1983-1989/remont/testing-diagnostics/#fuel-injection-system-bosch-afc) in this article.

Disconnect negative battery cable and remove electrical connector from cold start injector. Relieve fuel system pressure and remove fuel supply line from injector. Remove injector retaining bolts and remove injector. To install, reverse removal procedure.

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.

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 and 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, or mount injector in a vise.

Installation

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

ECCS Wiring Diagram. Scheme 48

See also:
• ECC CEC SYSTEM
• SPECIAL FEATURES
• PRESSURE REGULATOR CONTROL UNIT