How fuel injection systems work_fuel injection_fuel injection systems
Custom Search

Fuel Injection Systems

Welcome to our fuel injection systems page in our web site, in this page we will explain how fuel injection systems work, this information will help you to diagnose problems related to the fuel injection system on your car.


Fuel Injection Systems


There are two kinds of common fuel injection systems used in automobiles, mechanical fuel injection, and electronic fuel injection, we will discuss in this page how electronic fuel injection works; this is the system used in today's vehicles.

There are several parts involved in the fuel injection system, the most common are: fuel pump, fuel pump strainer, fuel filter, fuel lines, fuel pressure regulator, fuel rail, fuel injectors, electronic control computer (ECM), fuel pump relay, mass air flow sensor, map sensor, oxygen sensor, throttle position sensor, air temperature sensor, idle air control valve or idle speed motor, coolant temperature sensor, crank shaft position sensor, camshaft position sensor, and throttle body assembly.

These are the most common parts used in most vehicles with electronic fuel injection, every make and model varies the amount of items used in their systems, and they may name each part different, but all systems have the same principle and that is to inject the right amount of fuel to the engine to maintain the right combination of air and fuel to have proper combustion and reduce pollution.

The basic operation is as follows:
When you turn  the key on in your car the engine control computer sends a signal to the fuel pump relay and energizes the fuel pump for a few seconds, if you try to start the car the signal will remain on and the fuel pump will continue to pump fuel, this is also true once the car is running, the fuel pump forces the fuel from the fuel tank at a certain pressure depending on the pump and the  make and model,  please note that the fuel pump's pressure will always be greater than the pressure needed by the vehicle, the job of the fuel pressure regulator is to maintain the proper fuel pressure and will allow the rest of the fuel to exit through the return line that takes the excess fuel back to the fuel tank, also note that before the fuel enters the fuel rail, it passes through the fuel filter, the fuel filter's job is to remove any solid particles contained in the fuel that could clog the fuel injectors and harm the operation of the fuel system.

Once the fuel enters the the  rail (fuel injectors and fuel pressure regulator are attached to the fuel rail), it is distributed to the fuel injectors, the fuel injectors can't inject any fuel yet, even if the right amount of fuel and fuel pressure are kept in the system, the fuel injectors are operated by the engine control computer, the computer will send a signal to each injector at the right time to inject fuel in each cylinder; the amount of fuel injected is controlled by the length of time the signal remains on for the fuel injector, and this signal will vary depending on the conditions the car is being driven under, either idling, cruising speeds, or under acceleration, during acceleration the signal will remain on longer than at idle and cruising speeds, (this signal is sent on and off in milliseconds).
Ok. We know that the engine control computer sends the signal to each cylinder at the right time, but, how does it know when?




To identify which cylinder needs the fuel, the engine control computer (ECU), receives the information from two sensor, one is the crankshaft position sensor, it is usually located on the front of the engine in the timing cover near the crankshaft pulley, on the side of the engine block on the lower part near the crankshaft, or on the transmission bellhousing near the flywheel, every make and model places this sensor in different locations, but the way it works is the same, it sends a signal to the computer telling it the position of the crankshaft, to make the information more accurate, the camshaft position sensor sends a signal letting the computer know where piston number one is, based on this information the computer knows which cylinder needs fuel at what time based on the firing order of the vehicle.

It is not enough to just inject fuel and hope for the best!!, there is a need to inject the right amount too, this is done by the engine control computer also, the mass air flow sensor tells the computer how much air is coming in to the engine, the map sensor lets the computer know how much vacuum the engine has, the air temperature sensor lets the computer know the temperature of the air entering the engine, the coolant temperature sensor lets it know what the temperature of the engine is, the throttle position sensor lets it know how much you are accelerating, the idle air control valve regulates the amount of air coming in to the engine when you are not accelerating ( at idle), the oxygen sensor lets the computer know how much oxygen is leaving through the exhaust system, based on all this information, the computer will make adjustments in fractions of a second!!, over and over again, to maintain the right amount of fuel and air in your car for proper combustion, to aid fuel economy and reduce pollution. A system designed to help reduce emissions is the EGR system.