How they work: “The EFI (Cont’d)”

As we saw earlier, the engine control unit (ECU, the computer that controls all of the electronic components on your engine) “sees” the throttle valve open and increases the fuel rate in anticipation of more air entering the engine. It is important to increase the fuel rate as soon as the throttle valve opens; otherwise, when the accelerator pedal is first pressed, there may be a hesitation as some air reaches the cylinders without enough fuel in it. There are sensors that monitor the mass of air entering the engine, as well as the amount of oxygen in the exhaust. The ECU uses this information to fine-tune the fuel delivery so that the air-to-fuel ratio is just right. One could authoritatively say that, a fuel injector is nothing but an electronically controlled valve. It receives pressurized fuel from the fuel pump in the car, and it is able to open and close many times per second in its effort to control the inflow of the combustible substance. Whenever the injector is powered, an electromagnet opens the valve, allowing the pressurized fuel to squeeze out through a tiny nozzle. The nozzle is designed to turn the fuel into as fine a vapour as possible so that it can burn fast and easily. The amount of fuel supplied to the engine is determined by the amount of time the fuel injector stays open. This is called the pulse width, and it is controlled by the ECU. The injectors are mounted in the intake manifold so that they spray fuel directly at the intake valves. A pipe called the fuel rail supplies pressurized fuel to all of the injectors. In order to provide the correct amount of fuel for every operating condition, the engine control unit (ECU) has to monitor a huge number of input sensors (Engine Sensors). These are in charge of the inflow of fuel, they include; the mass airflow sensor that Tells the ECU the mass of air entering the engine ; Oxygen sensor(s), Monitors the amount of oxygen in the exhaust so the ECU can determine how rich or lean the fuel mixture is and make adjustments accordingly; Throttle position sensor – that Monitors how much air goes into the engine so that the ECU can respond quickly to changes, increasing or decreasing the fuel rate as necessary; the Coolant temperature sensor allows the ECU to determine when the engine has reached its proper operating temperature; the Voltage sensor - Monitors the system voltage in the car so the ECU can raise the idle speed if voltage is dropping as a result of a high electrical load; the Manifold absolute pressure sensor, Monitors the pressure of the air in the intake manifold. The amount of air being drawn into the engine is a good indication of how much power it is producing; and the more air that goes into the engine, the lower the manifold pressure, so this reading is used to gauge how much power is being produced. Finally, the engine speed sensor monitors engine speed, which is one of the factors used to calculate the pulse width. There above fall in two main types of control for multi-port systems: The fuel injectors can all open at the same time, or each one can open just before the intake valve for its cylinder opens (this is called sequential multi-port fuel injection). The advantage of sequential fuel injection is that if the driver makes a sudden change, the system can respond more quickly because from the time the change is made, it only has to wait only until the next intake valve opens, instead of for the next complete revolution of the engine. eddie@afrowebs.com