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4 pin VS 3 pin ignition coils

EFI Tuning Fundamentals

Discussion and questions related to the course EFI Tuning Fundamentals

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Could someone please explain the difference between a 3 pin and 4 pin direct coil from what I understand. 4 pin has an earth to the ecu. Is this correct and what would happen if you left this unplugged on an ecu with 3 pin wiring

You need to be more specific, number of pins doesnt mean anything. Some 3 pin coils dont even have internal ignitors. Some 4 pin coils the 4th wire is just feedback and doesnt need to be connected, on others it is the signal ground and needs to be connected. What coils are you playing with?