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Engine management system

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The electronic fuel injection system (EFI) delivers the precise amount of fuel/air mixture at the exact time it’s required by utilising various sensors and control devices.

Find out more about the main components of the electronic fuel injection system. 

Electronic control unit (ECU)

• The ECU is a computer, which translates information received from various sensors and calculates the correct fuel/air mixture for any given situation.
• It then energises the injectors to deliver the fuel and signals the distributor to provide a spark.

Fuel injectors

• The fuel injector is an electro-mechanical device, which delivers the fuel in a fine spray mist into the induction system.
• Fuel is delivered under pressure to the top of the injector and this fuel is released into the inlet manifold when the ECU sends an electric pulse.
• The amount of fuel delivered is determined by the length of time the injector is pulsed.
• There are two main types of injector systems:
  • Single-point injection is one injector mounted in a throttle body.
  • Multi-point injection is one injector per cylinder mounted in the inlet manifold.

Air flow metre

• The air flow metre measures the quantity of air drawn into the engine.
• The ECU uses the signal from the air flow meter to determine the amount of fuel needed to supply the optimum air/fuel mixture.

Engine temperature sensor

• Because the amount of fuel required by the engine varies ie: cold engines require more fuel (richer air/fuel mixture), the ECU needs to establish the engine temperature.
• It does this by means of an engine coolant temperature sensor.

Air temperature sensor

• The air temperature sensor sends a signal to the ECU to indicate a varying of air temperature, which effects air density and the need for richer or leaner fuel mixtures.
• The sensor is located in the inlet ducting or inside the air flow metre.

Electric fuel pump

• The fuel pump is located either in the fuel tank or somewhere on the fuel line.
• The purpose of the fuel pump is to deliver a constant flow of fuel to the injectors at a regulated pressure.
• The ECU signals the fuel pump to run when the ignition key is turned to the start position.

Fuel filter

• The fuel filter is fitted in the fuel line between the fuel pump and the injectors.
• In fuel injected cars this filter is a metal canister with a paper element inside.
• Great care should be taken when changing the filter as the fuel line is under pressure and the system needs to be depressurised before dismantling.
• It is a job best left to the experts.
• Check the owner’s manual for details on service intervals.

Fuel pressure regulator

• A predetermined fuel pressure is maintained in the line by the pressure regulator.
• There are two types of regulator:
  • A spring-controlled regulator is used with single point injection systems.
  • A diaphragm type regulated by manifold pressure is used in multi-point systems.

Auxiliary air valve

• Carburettors have a throttle by-pass to allow the engine to idle at a higher speed during warm up and when the electrical system is under load (air conditioning on at idle or lights on).
• The fuel injection system uses an auxiliary air valve to perform this task.

Throttle position switch

• The throttle position switch is mounted on the throttle body and informs the ECU of the position of the throttle flap.
• The ECU determines whether the engine is idling, accelerating or at full throttle and the ECU adjusts the fuel mixture to suit.

Crank angle sensor

• The crank angle sensor gives the ECU an indication of engine speed and number one piston position reference for injection timing.

Oxygen sensor

• The oxygen sensor sometimes called the lambda sensor in located in the exhaust manifold or front exhaust pipe and provides feedback to the ECU to control the fuel mixture.
• It measures oxygen content in the exhaust gases and sends a signal to the ECU, which adjusts the injection duration relevant to the information and ensures the optimum fuel mixture and the minimum exhaust emissions.

General information

• The engine management system has a warning light in the instrument cluster, usually called the engine light or engine control management light (ECM) light.
• The ECU constantly monitors feedback from all the sensors and if a fault occurs, ignites the light to warn the driver.
• If your light comes on, take the vehicle to the nearest dealer for diagnosis.
• When a fault occurs, even for a short duration, the ECU will record the fault as a code and the technician can then read this using specialised equipment.
• In general engine management systems have a limp-home mode, which allows the driver to continue the journey in the event of a system fault.
• In this situation the ECU uses preset values and operates the system at a reduced performance level.

Ignition system

• Engine management systems incorporate the ignition system by controlling spark timing to optimise performance and emission levels.
• There are two systems:
  • Distributor ignition - This system has what looks like a conventional distributor. But instead of contact points it uses an electronic device. The coil can be external to the distributor like the points ignition system or can be internal.
  • Direct ignition - The direct ignition system uses a coil for each cylinder or a coil for each pair of cylinders as in the Holden Commodore. The ECU fires the coil at the correct time using references from various sensors. The advantage of this system is that there is no distributor to wear out and the spark control is very precise.