652 Solenoidoperated Valve

This type of valve regulates the amount of air that by-passes the throttle valve through the medium of a solenoid-operated valve of the type shown in Fig. 6.15.

In the rest position shown, the valve (4) is closed by the spring (5) and the armature of the solenoid (2) is pushed back inside the solenoid coil (3). When operating, the energized solenoid opens the valve (4) and admits air to the induction system. The quantity of air admitted is controlled by duty cycle pulses that are sent from the ECM.

Testing a solenoid-operated valve

Figure 6.16 shows the portable oscilloscope being used to check the performance of a solenoid-operated idle speed control valve and Fig. 6.17 shows the pattern that can be expected as the ECM pulses the solenoid.

The suggested test conditions are that the valve's operation should be monitored when the engine is cold, when it is warming up, and when it is hot. It should be noted that different types of valve will produce different shaped patterns. The different shapes of the waveforms arise from the behaviour of inductive-type circuits. The pronounced saw tooth effect in Fig. 6.17(c) arises from the inductive reactance which is a feature of many inductive devices. Once again, we see the need to have good information about the product being worked on in order to make informed judgements about condition.

Fig. 6.17 Idle air bypass waveforms

Computer controlled purging of the charcoal canister is frequently performed by the operation of a (duty cycle) valve that is under the control of the ECM. The length of the 'on pulse' of the solenoid varies according to operating conditions.

Fig. 6.18 Testing the operation of the solenoid valve on a charcoal canister

Figure 6.18 shows the Fluke meter connected to the purge valve solenoid signal wire and earth. The meter shows a 30.3% duty cycle.

Were the oscilloscope to be used for this test the connections would be made in an identical way to the Fluke meter connections shown above. The pattern then obtained would show the characteristic shape similar to that shown for the test on the solenoid-operated idle valve. The 'on-pulse' length will vary as the ambient temperature and vehicle operating conditions change.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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