If we go back to the early electronic fuel injection, (EFI) systems known as batch-fired injectors or what was called simultaneous EFI systems, the bank 1 injectors were all fired together. The next engine revolution resulted in the powertrain control module (PCM) group firing the injectors from bank 2. When an injector electrically lost its resistance value or had a problem called pintle distortion, it created a rich condition on that specific cylinder and bank.