If your ecu is faulty then a piggy back wont help you. in general a piggyback is just that it sits on the back of your ecu and between the ancillaries and the ECU its self. It then overrides signals to ancillaries and feeds adjusted signals back to the ECU. If your ECU or any ancillaries are not working they still wont work.
If you have a faulty ECU, you either need a new ecu, fix yours or swap for a new system. sorry