Fuel injection - EFI system, Inputs, outputs and closed loop control.

A vehicle that utilizes EFI system will have major advantages over the conventional carburettor system; it is a more precise, efficient way of mixing fuel with air for internal combustion engine and an engine’s efficiency, performance, emission can be easily adjusted at a switch of a button.

An EFI system in the vehicle plays a major role in maintaining normal engine operation using three types of items only.

Inputs from sensors -> ECU Processing -> Outputs to actuators

ECU, or engine control unit, is the most vital item in an EFI system.  The purpose of its existence is to govern and monitor every aspects of the engine, process the engine data and respond to achieve the best performance and efficiency in accordance to engine condition and load.  These will all happen in a matter of milliseconds (and so as when the engine is starting, running, accelerating, decelerating, etc)

To do so it requires assistance from a set of input and output sensors/actuators.

Examples of input sensors for a typical EFI system:

- Throttle position sensor (TPS)

- Manifold absolute pressure sensor (MAP)

- Air flow mass sensor (AFM)

- Coolant temperature sensor

- Crank position sensor (CKP)

- Cam position sensor

- Air temperature sensor

- O2 sensor

- Knock sensor

Examples of output actuators for a typical EFI system:

-    Fuel injectors

-    Distributor

-    Fuel pump

-    Auxilary air valve

Input sensors provide information to the ECU using voltage signals, which is then processed in the micro processer in the ECU unit, the ECU then responds to the given data and adjusts the output actuator to suit.  This is to maintain the engine within the “safe” zone of detonation, while at the same time controlling air/fuel mixture, ignition timing, exhaust emission, etc.

Readings from the input sensors will differ in accordance to the engine’s load and condition; such as when the car is accelerating or wide open throttle (WOT), there will be change in air pressure inside the manifold and the MAP sensor will respond to it and send out a voltage signal to the ECU so to inform it that the engine load is not at idle anymore; the sudden change in throttle position (detected via TPS sensor), crank position and cam position, and the increased exhaust emission will indicate to the ECU that the vehicle is in fact accelerating, and hence instructs the fuel injectors and distributor to injects more fuel and advances its ignition timing to accommodate the change – this is all done by a step on the gas pedal.

Output actuators such as fuel injectors are devices that are activated by the ECU with reference to the engine’s load and condition it is in.  These actuators work with the input sensors in a “closed loop” system so any feedback to the engine operation will be recorded, processed and treated (e.g. The system recognises the motor is running rich according the O2 sensor signal, the ECU will consult with the data held in its “safe zone” table so to establish the necessary changes needed such as lowering the % duty cycle of the injectors to suit, etc) 

By the time the engine is started, the engine needs to get up to “operational temperature” so everything but the O2 sensor (the O2 sensor requires 300+ degrees temperature to operate) will be functional and the ECU uses this to constantly monitor and make changes with reference to the engine’s load and condition.  Temperature operated sensors such as O2 sensors and coolant temperature sensors have a direct effect to how rich or how lean an engine will run.  During cold start, the ECU will not be able to detect signal changes in O2 sensor signal and coolant temperature sensor so the ECU cannot adjust its fuel map, this is because the ECU uses O2 sensor signal and coolant temperature signals as references to how much shall the injectors be opened to inject fuel, hence the vehicle will be running rich in that period.  Once the engine gets up to “operational temperature” (and so as the two sensors), the ECU will now be able to sense the changes in signals and has the ability to alter fuel maps.  For a functional O2 sensor, it is common to see that it will constantly adjust between 0 – 5V at a constant motor RPM.

Running a close loop fuel control system enables precise engine management and increases the performance, reliability and efficiency of an internal combustion engine.  It plays a major role in maintaining the correct air/fuel ratio to achieve the best efficiency and combustion rate of the engine, at the same time monitoring it so any fault within the system can be remedied.  However if one of the component fails, this system may not be able to work to its full potential due to the false signals provided by the component at fault, the engine will run in “leap mode” and can potentially cause damage to other components if left running like so for a set period.  Hence replacing the fault component(s) are recommended, this can be found using a scan tool, trouble coding, or repaired in accordance to the manufacturer’s manual.

Ever since the 1980s, EFI systems have nearly taken over the conventional carburettor system for its simplicity, reliability, ease of operation, low initial cost and is considered a better system to maintain the performance, fuel economy, emission and close monitoring of an internal combustion engine – We will most likely see more new vehicles utilizing this system, or similar systems in the future.