One of the most common signs of a failing ignition coil is a misfire. If your vehicle is experiencing intermittent or persistent misfires, it's a good idea to have the ignition system checked out by a professional mechanic. Other symptoms of a failing ignition coil can include engine vibration, loss of power, and decreased fuel economy. Ignition coils can fail either gradually or suddenly, so it's important to be aware of the symptoms and get your vehicle diagnosed and repaired as soon as possible if you suspect an issue.