Transistorized ignition was first used on 1974 4M engines sold in California. With the introduction of 1975 models, usage has been extended to all Toyota vehicles sold in the United States.
The transistorized ignition system employed by Toyota works very much like the conventional system previously described. Regular breaker points are used, but instead of switching primary current to the coil off-and-on, they are used to trigger a switching transistor. The transistor, in turn, switches the coil primary current on and off.
Since only a very small amount of current is needed to operate the transistor, the points will not become burned or pitted, as they would if they had full primary current passing through them. This also allows the primary current to be higher than usual because the use of a higher current would normally cause the points to fail much more rapidly.
As already stated, the condenser is used to absorb any extra high voltage passing through the points. Since, in the transistorized system, there is no high current, no condenser is needed or used.
As a result of the lower stress placed on them, the points only have to be replaced every 24,000 miles instead of the usual 12,000 miles.
The Toyota transistorized ignition system may be quickly identified by the lack of a condenser on the outside of the distributor and by the addition of a control box, which is connected between the distributor and the primary side of the coil.
A fully transistorized ignition system was introduced in 1977. The system, including an ignition signal generating mechanism instead of the normal contact points, became the standard ignition system on all models from 1978.
The mechanism consists of a timing rotor, a magnet and a pick-up coil, all mounted in place of the points inside the distributor. As the signal rotor spins, the teeth on it pass a projection leading form the pick-up coil. When this happens voltage is allowed to pass through the system, firing the spark plugs. There is no physical contact and no electric arcing, hence no need to replace burnt or worn parts.
Basically, the transistorized ignition is serviced just like its conventional counterpart. The points must be checked, adjusted, and replaced in the same manner. Point gap and dwell must be checked and set. The points should also be kept clean and should be replaced at 24,000 mile intervals. Of course, since there is no condenser, it does not have to be replaced when the points are.
However, there are several precautions to observe when servicing the transistorized ignition system.
- Use only pure alcohol to clean the points. Shop solvent or an oily rag will leave a film on the points which will not allow the low current to pass.