133 Distributorless Ignition System

Figure 1.6 shows an ignition system for a four-cylinder engine. There are two ignition coils, one for cylinders 1 and 4, and another for cylinders 2 and 3. A spark is produced each time a pair of cylinders reaches the firing point which is near top dead center (TDC). This means that a spark occurs on the exhaust stroke as well as on the power stroke. For this reason, this type of ignition system is sometimes known as the 'lost spark' system.

Engine Load (Vacuum)

Engine Load (Vacuum)

Fig. 1.6 A distributorless ignition system

Figure 1.6 shows that there are two sensors at the flywheel: one of these sensors registers engine speed and the other is the trigger for the ignition. They are shown in greater detail in Fig. 1.7 and they both rely on the variable reluctance principle for their operation.

An alternative method of indicating the TDC position is to use a toothed ring, attached to the flywheel, which has a tooth missing at the TDC positions, as shown in Fig. 1.8. With this type of sensor, the TDC position is marked by the absence of an electrical pulse. This is also a variable reluctance sensor. The other teeth on the reluctor ring, which are often spaced at 10° intervals, are used to provide pulses for engine speed sensing.

Fig. 1.7 Details of engine speed and crank position sensors

TDC Peg

Fig. 1.7 Details of engine speed and crank position sensors

Fig. 1.8 Engine speed and position sensor that uses a detachable reluctor ring
Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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