Q: Must you replace all ignition coils or faulty ones only for 2010 BMW 550i GT?.

Ignition coils can be individually replaced without concern as to engine operation however fuel injectors are a different matter. If you replace one fuel injector, the other 7 fuel injectors should be removed from the fuel rail and professionally cleaned. If you just replace one injector, you could end up with an imbalance in fuel delivery because the other 7 injectors could have varying degrees of blockage that has built up over the years. Unless the car were brand new, if one injector has failed, the optimal practice is to remove all fuel injectors from the fuel rail and send them to a lab such as Mr. Injector for ultrasonic cleaning on a machine. During such service, the tiny filter baskets in each injector are removed and new filters are installed, and then each injector’s output and spray pattern is measured and documented. If a problem with balance (excessive variance in injector output) is detected during this service you are informed and then the necessary steps can be taken. If you desire that a certified mechanic provide a diagnostic and recommend a repair strategy, please request a fuel injector inspection/diagnostic and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.