Topic: Ignition System Evolution

Conventional Systems -- Breaker Point Ignition

A conventional system controls the power interruption to the coil primary winding with a set of breaker points and a condenser. The points work like a switch, alternately turning the coil primary circuit on and off. The condenser acts like an electronic shock absorber. When the points open, the power from the coil is absorbed in the condenser. When the points close again, the condenser discharges that power back into the circuit. This reduces point arcing and prevents the contacts from burning. The rotor, which is attached to the distributor shaft, direct the secondary voltage to each of the distributor cap terminals. The distributor cap then routs the secondary voltage to each spark plug in the firing sequence via the plug wires.

Point Alignment

Points Burned

Breaker Point Service Issues

Each ignition system has its own set of common failures. Breaker point systems have several inherent problems. They simply wear out due to friction, heat, and high resistance. As the rubbing block rides on the distributor cam it begins to wear. Over a period of time the air gap between the point set gets smaller. This normal wear causes the dwell angel to change which causes the ignition timing to go out of specifications.

Breaker Point Failures

Periodic adjustments are necessary to keep the system within factory settings. If the point gap is too wide the dwell time will be reduced, and the coil's magnetic field will be too weak to produce enough voltage that can arc across the spark plug gap. It takes about 10 milliseconds for the coil to saturate and produce high secondary voltage. When the dwell time is reduced, you usually wind up with a misfire.

Condenser Shorts

Coil Arching

Other Failures

Condensers short internally or the wire shorts to ground. High secondary resistance can cause the coil to arc to ground. Both of these conditions can cause engine misfire.