Fuel Injection Types In multi-point injection may be either sequential or simultaneous. A simultaneous system fires all 4 injectors at the same time with each cylinder receiving 2 injection pulses per cycle (720° crankshaft rotation). A sequential system receives just 1 injection pulse per cycle, timed to coincide with the opening of the inlet valve. As a very rough guide the injector pulse widths for an engine at normal operating temperature at idle speed are around 2.5 ms for simultaneous and 3.5 ms for sequential. An electromechanical injector of course takes a short time to react, as it requires a level of magnetism to build before the pintle is lifted off its seat. This time is called the (solenoid reaction time). This delay is important to monitor and can sometimes occupy a third of the total pulse width. The waveform is (split) into two clearly defined areas. The first part of the waveform is responsible for the electromagnetic force lifting the pintle, in this example taking approximately 0.6 ms. At this point the current can be seen to level off before rising again as the pintle is held open. With this level off it can be seen that the amount of time that the injector is held open is not necessarily the same as the time measured. It is not however possible to calculate the time taken for spring of the injector to fully close the injector and cut off the fuel flow. This test is ideal for identifying an injector with an unacceptably slow solenoid reaction time. Such an injector would not deliver the required amount of fuel and the cylinder in question would run lean. Depending on the system encountered, the injectors can fire either once or twice per cycle. With simultaneous injection the injectors are wired in parallel and 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) configuration engines. The fuel is delivered to each bank alternately. In the case of a Jaguar V12 the injectors are fired in 4 groups of 3 injectors. Because of the frequency of the firing of the injectors, a sequential injector normally has twice the duration, or opening time, of a simultaneous pulse. This is, however, determined by flow rate of the injector and operating pressure of the fuel.