651 Stepper Motoroperated Valve

Figure 6.12 shows a simplified arrangement of the extra air (air by-pass) valve that is built into the throttle body of some petrol injection systems.

The ECU pulses the transistor bases, in the correct sequence, so that the stepper motor moves the air valve to provide the correct air supply, for any given condition. In addition, other sensor signals will enable the ECU to provide the correct amount of fuel to ensure that the engine continues to run smoothly.

Figure 6.13 shows the stepper motor with the air valve attached. The multiple pin connection is typical of the type of connection that is used to electrically connect the stepper motor to the ECU. The stepper motor can normally be checked

Fig. 6.13 The stepper motor and extra air valve (Lucas)
Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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