If your Ford Focus stalls while you are driving, there may be one or more components that are defective. To find out which ones may be causing your car to stall, perform a few simple inspections.
Inspect the Fuel System
Faulty components, such as your Focus' fuel injectors, fuel line, fuel pump or fuel filters can cause problems relating to your car's engine not getting appropriate amounts of fuel. Also, you may be using inefficient fuel, if you switched over to cheaper gas that is not right for your car.
Inspect the Electrical System
Problems with a defective coil pack, alternator, spark plugs or sensors can lead to stalling due to improper electrical functions. Inspect your spark plugs and sensors, which tie into the fuel system. Test the power in your car while driving by activating your car's electronics to see how much you can power on before the car begins to stall. Examine your car's coil pack for damage.
Inspect the Emissions System
Your Focus' emissions system may not be functioning properly, which also could lead to engine misfiring and backfiring while you are driving. Such problems within this system can cause noise while driving.