MPFI

Multi-point fuel injection injects fuel into the intake port just upstream of the cylinder's intake valve, rather than at a central point within an intake manifold. MPFI (or just MPI) systems can be sequential, in which injection is timed to coincide with each cylinder's intake stroke, batched, in which fuel is injected to the cylinders in groups, without precise synchronization to any particular cylinder's intake stroke, or Simultaneous, in which fuel is injected at the same time to all the cylinders. Many modern EFI systems utilize sequential

MPFI; however, it is beginning to be replaced by direct injection systems in newer gasoline engines. The multi-point injector is an electromechanical device which is fed by a 12 volt supply from either the fuel injection relay or from the Electronic Control Module (ECM). The voltage in both cases will only be present when the engine is cranking or running, due to both voltage supplies being controlled by a tachometric relay. The injector is supplied with fuel from a common fuel rail.

The length of time that the injector is held open for will depend on the input signals seen by the engine management ECM from its various engine sensors. These input signals will include:-

· The resistance of the coolant temperature.

• The output voltage from the airflow meter (when fitted).

• The resistance of the air temperature sensor.

• The signal from the Manifold Absolute Pressure (MAP) sensor (when fitted).

• The position of the throttle switch / potentiometer.

The held open time or injector duration will vary to compensate for cold engine starting and warm-up periods, i.e. a large duration that decreases the injection time as the engine warms to operating temperature. Duration time will also expand under acceleration and contract under light load conditions.

Depending on the system encountered the injectors can fire either once or twice per cycle. The injectors are wired in parallel with simultaneous injection and will all fire together at the same time. Sequential injection, as with simultaneous, has a common supply to each injector but unlike simultaneous has a separate earth path for each injector. This individual firing allows the system, when used in conjunction with a phase sensor, to deliver the fuel when the inlet valve is open and the incoming air helps to atomize the fuel. It is also common for injectors to be fired in 'banks' on 'V' configured engines. The fuel will be delivered to each bank alternately, because of the frequency of the firing of the injectors, it is expected that a sequential injector will have twice the duration, or opening, than that of a simultaneous pulse. This will however be determined by the injector flow rate.