FAQ: DFCDI - COIL COMPATIBILITY
Many users enquire about the compatibility of Autronic Capacitor Discharge Ignitions and Original Equipment Manufacturer (OEM) ignition coils. Use of these OEM coils is convenient and physically neat, especially when Coil on Plug (COP) coils are used. In many applications these coils are suitable. Coils with inbuilt igniters or with an internal electrical connection between the primary (low voltage) winding and ground are unsuitable and MUST NOT BE USED. Some OEM coils are unable to withstand the additional stress imposed by high power capacitor discharge ignition and may have a high incidence of failure. Failure due to internal insulation breakdown can be minimized by NOT operating the Ignition when the coil is disconnected from its spark plug.
These OEM coils when connected singly to a single CD ignition, generally perform satisfactorily for moderately boosted forced induction engines. For heavily boosted engines a coil specifically designed for use in capacitor discharge ignition systems will generally provide superior performance.
When connecting 2 coils (OEM or Aftermarket) to a single CD ignition output for waste spark applications, the coils electrical properties determine their suitability and if suitable, the correct method of connection. Incorrect connection will cause spark energy to be diverted away from the cylinder on its compression stroke, resulting in engine misfire under heavy load operation. The electrical property “mutual inductance”, a measure of the electrical coupling between the coils’ primary and secondary windings is the determining property. Low mutual inductance coils have tightly coupled windings and are only suitable for series electrical connection. High mutual inductance coils have loosely coupled windings and are only suitable for parallel electrical connection. Coils with intermediate mutual inductance have moderately coupled windings and are unsuitable for either series or parallel electrical connection and should not be used. See the Autronic wiring diagrams for the relevant series and parallel connection method that suits your coils. If uncertain of the characteristics of your coils, it is recommended that each pair be replaced with a doubled ended coil specifically designed for use in capacitor discharge ignition systems.