Fuel injection system – general information

The fuel injection systems used on all vehicles covered by this manual are the sequential multi-port type. This means that there is a fuel injector in each intake port, and that they inject fuel into the intake ports in the cylinder firing order. The injectors are turned on and off by the Powertrain Control Module (PCM). When the engine is running, the PCM constantly monitors engine operating condi­tions with an array of information sensors, cal­culates the correct amount of fuel, then varies the interval of time during which the injectors are open. Sequential multi-port systems pro­vide much better control of the air/fuel mixture ratio than earlier fuel injection systems, and are therefore able to produce more power, better mileage and lower emissions.

The fuel injection system uses the PCM and an array of information sensors to deter­mine and deliver the correct air/fuel ratio under all operating conditions. The fuel injec­tion system consists of three sub-systems: air induction, electronic control and fuel delivery. The fuel injection system is also closely inter­related with PCM-controlled emission control systems. For additional information about the PCM, the information sensors and the emis­sion control systems, refer to Emissions and engine control systems.

Air induction system

The air induction system consists of the air filter housing assembly, the air intake duct, the throttle body and the intake mani­fold. The throttle body contains a throttle plate that regulates the amount of air entering the intake manifold. The throttle plate is opened and closed by the PCM in response to input from the Accelerator Pedal Position Sensor (APPS). The lower part of the throttle body on some engines is heated by engine coolant to prevent icing in cold weather. The throttle body is also the location of the Throttle Posi­tion (TP) sensor; this monitors the opening angle of the throttle plate and sends a signal to the Powertrain Control Module (PCM). The Manifold Absolute Pressure (MAP) sensor is also located on the throttle body. The MAP sensor measures intake manifold pressure/ vacuum and generates a signal that’s propor­tional to the pressure or vacuum. The PCM uses this data to calculate the load on the engine. Another information sensor, the Intake Air Temperature (IAT) sensor, is located on the intake manifold. The IAT sensor relays a signal to the PCM that varies in accordance with the temperature of the incoming air. The

PCM uses this data to calculate how rich the air/fuel mixture should be. All of the air induc­tion components (air filter housing, air intake duct and throttle body) are covered in this Chapter, except for the intake manifold, which is covered in 3.7L V6 and 4.7L V8 engines ; Hemi engine ; Diesel engine ; 3.6L V6 engine , and the information sensors, which are covered in Chapter Emissions and engine control systems.

Electronic control system

For more information about the elec­tronic control system, its information sensors and output actuators, refer to Emissions and engine control systems.

Fuel delivery system

The fuel delivery system consists of the fuel pump, the fuel filter/fuel pressure regu­lator, the fuel rail and fuel injectors, and the hoses, lines and pipes that carry fuel between all of these components. For more information about the fuel lines and the various types of fittings used on different models, refer to Fuel lines and fittings – repair and replacement.

The fuel pump is an in-tank design. Fuel is drawn through a strainer at the pump inlet, then pumped out the other end of the pump and through a fuel filter, which is an integral part of the fuel pressure regulator. The fuel fil­ter/fuel pressure regulator, which is mounted on top of the fuel pump/fuel level sending unit module, maintains the fuel pressure within the specified operating range. When the operat­ing pressure exceeds the specified operat­ing range, the pressure regulator opens and sends the excess fuel back into the fuel tank (there is no return fuel line from the fuel rail back to the tank). After the fuel has been fil­tered, it’s pumped through a fuel supply line to the fuel rail on the engine.

The fuel rail, which is bolted to the intake manifold, functions as a reservoir for pressur­ized fuel so that there’s always enough fuel available. The upper end of each injector is inserted into the fuel rail and the lower end of each injector is inserted into the intake manifold. Each end of each injector is sealed by an 0-ring.

Each fuel injector is a solenoid-actuated, pintle-type design consisting of a solenoid, plunger, valve, and housing. When the engine is running, there is always voltage on the hot side of each injector terminal. Injector drivers inside the PCM turn the injectors on and off by switching their ground paths on and off. When the ground path for an injector is closed by the PCM, current flows through the solenoid coil, the ball or needle valve rises and pressurized fuel inside the injector housing squirts out the nozzle into the intake port directly above the intake valve (s). The quantity of fuel injected each time an injector opens is determined by its pulse width, which is the length of time dur­ing which the valve is open.