Simultaneous and Sequential
Simultaneous and Sequential
Injection The port fuel injection (PFI) or multi-point (MFI) systems have individual injectors for each cylinder. The injectors are fitted so that fuel is sprayed into the inlet
Types of fuel injection systems
ports. Port fuel injection systems are either simultaneous, where all injectors operate at the same time, or sequential, where each injector operates on the induction stroke for each cylinder in turn.
Gasoline Direct Injection (GDi) A recent development has been the Introduction of a direct injection petrol engine where the fuel is injected
Mitsubishi GDi
into the combustion chamber.
Engine Control Module Modern petrol injection systems are linked to the ignition systems and are controlled by an engine control module (ECM). The latest developments have all electronic systems
Ignition and fuel systems are
linked to form a power train control
combined
module (PCM). This is also described as a vehicle control module (VCM). All modern fuel injection systems have closed loop electronic control using an exhaust gas oxygen sensor. For clarity, each electronic control unit will be referred to as an ECU.
Inputs and Outputs The components for any electronic fuel injection system can be divided into four groups: The air supply components, the fuel supply components, the electronic control unit (ECU),
EFi components
together with the power supply and system harness and the sensors which provide data to the ECU.
Air Supply Components The air supply components consist of ducting and silencing components between the air intake and the inlet manifolds. This will also include an air filter, a throttle body,
Air supply
throttle plate assembly and idle control components. The air supply components must provide sufficient clean air for all operating conditions. The air flow into the engine would be noisy and unbalanced between cylinders without the use of resonators and plenum chambers. A plenum chamber is a large volume air chamber that can be fitted either in front of or behind the throttle plate housing.
Air Filter Air filters on most modern petrol engined vehicles consist of a plastic casing with a paper filter element. Air flow into the filter is
Air filter on a
upwards so that dust and dirt particles drop into modern vehicle the dust chamber, or is rotary so that dust and dirt is thrown out before the air enters the engine. Crankcase ventilation and the air supply or pulse air exhaust emission systems, are also connected to the filter assembly.
Throttle Body The throttle is a conventional circular plate in an air tube. For fast idle and warm up, an auxiliary air valve is fitted to bypass
Throttle body
the throttle plate, or an electromechanical link is assembly made to the throttle plate spindle. An auxiliary air valve, idle air control valve (IAC) or idle speed control valve (ISC) is operated from signals from the ECU.
Auxiliary Air Valve Early designs of the auxiliary air valve use a disc with a calibrated aperture for closing or opening the bypass air channel. The disc is held closed by a pull off spring and opened by a bimetal spring. When the engine is cold, the bimetal spring bends to open the valve. With the engine running, an electrical heating current acts on the bimetal strip. This causes it to bend and allow the pull off spring to close the air channel.
Rotary Air Valve A later development of the auxiliary air valve is the rotary air valve. This has a special electric motor to move and hold the valve in position. The position is based on the electrical signals supplied by the ECU. Two electric windings in the motor work in opposition to each other so that the motor is variable over a 90° arc.
Solenoid Valve Other designs of auxiliary or ‘extra air’ valves have graduated opening values based on the strength of current supplied from
Solenoid air valve
the ECU. These valves operate to hold the idle speed to the stored data specification for engine temperature and load conditions. The valve consists of a solenoid valve with a spring-loaded armature connected to the valve in the air channel.
Air Bypass The amount of air allowed to flow through the bypass channel of the auxiliary air valve is regulated by the position of the valve. At idle, the valve is continuously adjusted to stabilise the speed. When the throttle is closed during deceleration the valve plate is adjusted to control exhaust emissions. During engine starting, the valve is open and when the engine is switched off the valve is in the rest position.
Idle Speed Control Idle speed control can also
be provided by direct action onto the throttle spindle. Electric solenoids or stepper motors are
Throttle idle
used for this method of control. The solenoids
speed control
can be single position or multi-position types and can be used for not only cold start and warm up control but also to open the throttle when high load systems, such as the air conditioner, are switched on. Stepper motors give graduated positions depending on the supply current to a number of electric windings. Sensors in the idle control mechanisms provide feedback signals to the ECU to provide data on operation and position.
Fuel Supply The fuel supply from the fuel tank to the injector valves for all electronic systems follows the same basic layout. The delivery of fuel at the injector valves is also based on a similar
Fuel supply components
function for all systems. A basic layout of fuel supply components is shown here.
A fuel pump is fitted either in, or close to, the fuel tank. A fuel filter is fitted in the delivery fuel lines from the tank to the fuel rail. A fuel pressure regulator is fitted on either the housing for throttle body injector systems, or the fuel rail for port fuel injection systems. The return fuel lines run from the pressure regulator to the fuel tank.
Fuel Pump The fuel pump is a roller cell pump driven by a permanent magnet electric motor. Fuel flows through the pump and motor but there is no risk of fire as there is never an
Roller cell pump
ignitable mixture in the motor. The delivery pressure is set by a pressure relief valve, which allows fuel to return to the inlet side of the pump, when the operating pressure is reached. There is a non-return valve in the pump outlet. Typical delivery pressures are between 300 and 400 kPa (3 to 4 bar).
Roller Cell Pump The rollers in the roller cell pump are thrown out by centrifugal force when the motor armature and pump rotor spindle rotate. The rotor is fitted eccentrically to the pump body and as the rollers seal against the outer circumference, they create chambers that increase in volume to draw fuel in. They then carry the fuel around and finally discharge it as the chamber volume decreases.
Pump Electrical Supply The fuel pump electrical supply is live only when the engine is being cranked for starting or is running. The fuel pump electric feed is from a relay that is switched on with the ignition. Safety features are built into the electric control feed to the relay so that it operates only to initially prime the system or when the engine is running. The control functions of the fuel pump relay are usually provided by the fuel control module.
Inertia Switch A further safety feature is the use of an inertia switch in the feed from the relay to the fuel pump. This operates, in the event of an accident, to cut the electric feed to the fuel pump and to stop the fuel supply. It is an impact operated switch with a weight that is thrown aside to break the switch contacts. Once the switch has been operated it has to be manually reset.
Fuel Filters The fuel filter is an in-line paper element type that is replaced at scheduled service intervals. The filter uses micro-porous
An in-line paper
paper that is directional for filtration. Filters
element type
are marked for fuel flow with an arrow on the casing and correct fitting is essential.
Fuel Pressure Regulation The fuel pressure regulator is fitted to maintain a precise pressure at the
fuel injector valve nozzles. On And on throttle
Fuel pressure
regulators on rail… body
port fuel injection systems, a fuel rail is used to hold the pressure regulator and the fuel feed to the injector valves. The injector valves usually fit directly onto or into the fuel rail. The fuel rail holds sufficient fuel to dampen fuel pressure fluctuations and keep the pressure applied at all injector nozzles at a similar level.
Operation of the Fuel Pressure Regulator Fuel regulators are sealed units with a spring-loaded diaphragm and valve on the return outlet to the fuel tank. Fuel is pumped into the regulator and when the pressure is high enough, it acts against the diaphragm and compression spring to open the valve. Surplus pressure and fuel is allowed to return to the fuel tank. Once the pressure in the fuel regulator is reduced, the valve closes and the pressure builds up again. Throttle body injection systems operate in the region of 1 bar, and port fuel injection systems in the region of 2.5 bar.
Inlet Manifold Vacuum On port fuel injection systems, inlet manifold vacuum acts against the compression spring in the fuel pressure regulator. This is required in order to maintain a constant pressure differential between the fuel rail and the inlet manifold. With a constant pressure differential, the amount of fuel delivered during a set time will be the same irrespective of inlet manifold pressure.
Turbocharger For vehicles fitted with a turbocharger or supercharger, inlet manifold pressure is applied to the diaphragm and regulator valve. When the inlet manifold pressure rises above a certain value, the regulator valve is closed so that the full pump delivery pressure is applied to the injector valve nozzles. This raises the amount of fuel delivered to match the boosted air charge.
Injector Valves The injector valves spray finely atomised fuel into the throttle body or inlet ports depending on the system. The electromagnetic injection valves are actuated by signals from the ECU. The signals are of a precise duration depending on operating conditions but within the range of about 1.5 to 10 milliseconds. This open phase of the injector valve is known as the 'injector pulse width'.
Solenoid Injectors There is a range of individual injector valve designs but all have the same common features. These are an electromagnetic solenoid, with a spring-loaded plunger, connected to a jet needle in the injector valve nozzle. The electrical supply to the solenoid is made from the system relay or ECU. Earthing or grounding the other connection energises the solenoid. This lifts the plunger and jet needle so that fuel is injected for the duration that the electric current remains live. As soon as the electrical supply is switched off in the ECU, a compression spring in the injector valve acts on the solenoid plunger to close the nozzle.
Throttle Body Injector A fuel injector valve for a throttle body system is shown here. This cross section view shows the housing, the magnetic coil for the electric solenoid and the jet needle and nozzle.
Multi-point Injector A top feed fuel injector valve for port fuel injection systems is shown here. This type of valve is generally used on earlier systems. One problem experienced with this fuel feed arrangement is fuel vaporisation and bubbles forming in the fuel rail. The bubbles can cause starting and running problems. To overcome this problem lateral or side or bottom feed injectors are used. An example of this type is shown here. When fitted in the fuel rail it can be seen that any bubbles that may form will be at the top of the rail. They will therefore, be flushed out through the regulator as soon as the fuel pump is actuated.