A conventional point-type ignition system is used on all 4-121 engines. All other engines are equipped with electronic ignition.
1975 through 1977 engines use the Breakerless Inductive Discharge (BID) ignition system. The system consists of an electronic ignition control unit, a standard type ignition coil, a distributor that contains an electronic sensor and trigger wheel instead of a cam, breaker points and condenser, and the usual high tension wires and spark plugs. There are no contacting (and thus wearing) surfaces between the trigger wheel and the sensor. The dwell angle remains the same and never requires adjustment. The dwell angle is determined by the control unit and the angle between the trigger wheel spokes. In 1978 the system was modified to include a different ignition module and distributor, and was renamed Solid State Ignition (SSI).
The 4-151 engine uses the Delco-Remy High Energy Ignition (HEI) system.