There are several different symptoms that may surface if a car has a bad ignition coil, including backfiring, trouble starting the vehicle, engine misfires, stalling and poor gas mileage. Any one of these problems, or an aggregation of them, indicates a vehicle that has a dysfunctional ignition coil.
The ignition coil is the part of an automobile that takes power from a generator and transfers it to the spark plugs, igniting the fuel. This makes the vehicle start running and is a necessary part of the ignition process. However, it is possible for an ignition coil to become dysfunctional and cause a wide variety of car problems.
Because ignition coils are so important to the start-up process of a vehicle, they can cause problems when the car is turned on. If a vehicle has trouble starting up, there may be a bad coil. Regular and repeated backfirings are also a signal that a car's ignition coil is beginning to lose its functionality, according to DoItYourself.com. Sometimes a bad ignition coil has an impact on the car's gas mileage, causing it to become less fuel efficient over time. Other problems related to bad ignition coils include regular stalling and coughing, sputtering sounds when a car is started.