Injection Pulse Width and Frequency

In every Mitsubishi fuel injection system, injector nozzles open and close very rapidly in a series of pulses. The amount of fuel delivered per unit of time is controlled by varying the duration, or width, and frequency of the pulses while fuel pressure is held constant. Thus fuel delivery can be increased by increasing the width of each pulse, or by timing the pulses closer together i.e., increasing their frequency. The ECI computer controls this.

FIGURE 5:

Pulse Width

The basic injection pulse T(b) occurs at idle when the engine is warm. The pulse width is modulated by the computer in response to signals from the various sensors. See Fig. 5. Each logic circuit and memory in the computer connected with each sensor has its own modulation factor k(x) to change T. These relationships are explained mathematically on Page 10.

FIGURE 6:

Pulse Frequency

In normal operation, each injection is synchronized to the signal pulse from the air flow sensor. The computer divides the frequency of the pulse of the air flow sensor signal frequency by N (2, 3, or more), as shown in figure 6 below. An exception to this rule is the multi-point system in the 1986 and 1987 Galant. in the Galant system, the fuel injection pulses are synchronized to the ignition pulses.



The chart below shows the pulse width at idle, medium load, and heavy load conditions. Note that the modulating ratio 1/N is also given to give an idea of the frequency of pulsation.