I have a 78 280z with a 82 l28et, first the car ran great, took it down to the store and on the way back started to run funny and backfiring. the front three cylinders you can pull either the plug wire or the injector plug and does not effect the idle. checked the injector plugs at the injector and at the plug at the ecu and they have voltage, and when the cars running you can pull the plug wires and see arc coming off the plug wires, just at a point where i dont have a clue what it can be. bad plug wire, injector, ecu? any advice would be nice