Wasted Spark

Circuit diagram of the wasted spark ignition of the Citroën 2CV: battery, positive pole, indicator lamp, ignition lock, primary winding of the ignition coil, capacitor, breaker. Under the primary winding, the secondary winding of the ignition coil and spark plug pair.

Ignition coils of a Ford Escort RS1600i from 1981

As wasted spark ( english "wasted spark") is a type of ignition in internal combustion engines refer to operations of the spark plugs in two cylinders at the same time just before top dead center fire (OT), once at the end of the compression while the other cylinder during the ejection phase. The spark plugs are connected in series via the metal body of the cylinder head and share an ignition coil, the secondary winding of which must not be connected to the ground potential of the vehicle (as is usual with normal ignition coils). The ignition distributor is not required if a coil is installed for every two cylinders. This technique is mostly used with dormant ignition systems. The second ignition in the exhaust stroke normally has no effect on the engine performance, since there is no ignitable mixture at this point. In the event of poor mixture preparation, incorrect timing or incomplete combustion for any other reason, an ignitable mixture can arise in the event of a fault, which can lead to misfiring (exhaust pops).

From the 1980s and increasingly from the 1990s, vehicle manufacturers replaced the widespread ignition systems with mechanical ignition distributors with the much more modern wasted spark ignitions. In the recent past, this type of ignition has been increasingly replaced by ignition systems with individual ignition coils .