The fuel system includes components such as the fuel tank, fuel filler cap, fuel lines, a high-pressure fuel pump, PGM-FI main relay, filter, pressure regulator, injectors, and fuel pulsation damper. The fuel injection system delivers pressurized fuel to the injectors with the engine ON and cuts that fuel delivery when the engine is turned OFF .
The fuel is circulated in a pressurized loop from the fuel tank to the injectors and back to the fuel tank. That is why some of the components are labeled in and out, or feed and return, as the component must be installed properly. This is also useful when doing system diagnosis, because the fuel pressure characteristics could differ depending on where it is being checked.
The fuel is circulated in a loop so each fuel injector has a continuous supply of fuel. The fuel injectors are electrically operated and their operation is controlled by the Powertrain Control Module (PCM). Each injector has a small electromagnet, that when triggered by electricity, causes the injector to open and spray fuel. Sometimes an audible clicking noise can be heard from an electrically operated injector when the engine is running.
The fuel requirements for an engine differ depending on the temperature of the engine and the surrounding atmospheric conditions. A cold engine being started in freezing temperatures requires significantly more fuel to be delivered to the cylinders than a warm engine idling in a hot climate.
See Figure 1
Any atmospheric condition that affects the amount of available oxygen molecules in the air also affects the needed fuel mixture for a gasoline engine. The amount of available oxygen molecules in the air is affected by both temperature and altitude, and the fuel injection system must be able to adapt to ensure the correct fuel delivery for the engine to run properly.
During a cold engine startup more fuel is needed to get the engine started. The fuel does not atomize efficiently on a cold engine, as the fuel tends to enter the combustion chamber in the form of small droplets, which are more difficult to ignite than an atomized vapor. Once the engine has reached operating temperature, the fuel is atomized into a highly combustible vapor by the engine's increased operating temperature. This fuel vapor is much more combustible than raw fuel droplets, therefore the engine needs less fuel to operate.
To accommodate the ever-changing fuel requirements for an engine to run and perform properly, the PCM must be capable of monitoring the atmospheric conditions and the engine's operating parameters.
Engine related conditions that affect fuel requirements are engine operating temperature, engine speed (RPM), throttle position and engine load. Atmospheric conditions that affect an engine's fuel requirements are altitude and outside air (ambient air) temperature
Based on the information provided to the PCM via the input sensors, the PCM manages the fuel delivery by controlling the amount of time that it allows each injector to stay open. Because the fuel injectors are in a fuel loop where the pressure is relatively constant, the fuel mixture can be controlled by the amount of time a fuel injector stays open.
The added benefits of a precisely controlled fuel delivery system include reduced emissions, improved driveability, increased performance and improved fuel economy
The fuel injection system rarely requires maintenance and there are no routine adjustments to the fuel metering system that can be performed. Preventative maintenance tips that will help prolong the life of a fuel injection system include:
Safety is an important factor when servicing the fuel system. Failure to conduct maintenance and repairs in a safe manner may result in serious personal injury. Maintenance and testing of the vehicle's fuel system components can be accomplished safely and effectively by adhering to the following rules and guidelines.