631 Peak And Hold

Figure 6.3 shows the current flow in a peak and hold single-point injector. This behaviour is achieved by having two paths to earth that are controlled by the ECM, as shown in Fig. 6.4.

Figure 6.3 shows the current flow in a peak and hold single-point injector. This behaviour is achieved by having two paths to earth that are controlled by the ECM, as shown in Fig. 6.4.

1 Location of ballast resistor

2 MAP sensor

A Current in Amps B Time in milliseconds C Pickup current (Phase 1) D Holding current (Phase 2)

1 Location of ballast resistor

2 MAP sensor

A Current in Amps B Time in milliseconds C Pickup current (Phase 1) D Holding current (Phase 2)

Fig. 6.3 Electric current pattern in injector

Fig. 6.4 Injector circuit

The peak current occurs when the injector is first earthed through both circuits. After a short period the circuit without the resistor is switched off by the ECM. This effectively inserts the resistor into the injector circuit and leads to a reduction in the current flowing through the solenoid winding. An oscilloscope connected between the ECM side (earth) connection of the injector will show a pattern that reflects the current flow in the circuit. Because the current falls during the hold stage, there will be a rising edge in the voltage trace. This is not the end of the injector period because this comes when the rising edge that accompanies switching off occurs. In order to determine the length of the injector pulse from the scope pattern it is necessary to refer to the time from the first falling edge to the second rising edge of the scope trace.

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