The car should still run even with no ECU.

The car really has mechanical fuel injection. The ECU electronics are there only to fine-tune the fuel injection. It is not like "real" electronic fuel injection where the injectors open and close. The injectors just spray all the time with the amount of fuel going thru the injectors determined by the amount of fuel pressure.

You might attach a fuel pressure gauge and see if the fuel pressure drops and makes the engine quit. If pressure stays up, look to the ignition system.

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2012 E350
2006 Callaway SC560