Trying to diagnose a Ford engine that is running rough can be a tricky proposition. However, it is important to determine why the engine is running roughly, because running a vehicle like this for a sustained amount of time can cause permanent damage. There are several ways to determine if the coil packs are causing this issue, which makes troubleshooting the coil packs on your Ford one of the first places to start.
Misfiring and Stalling
When a vehicle has a weak coil pack, the engine will misfire. You can tell misfiring because your Ford will feel like it's going to stall when idling. This means the engine will not run smoothly, but will sound choppy and the car may even shake. If more than one coil is weakened or not working, the vehicle may completely stall.
OBD II Testing
According to AsaShop.org, the coil packs can be tested with an OBD II (on board diagnostic, generation two) tester. An OBD II tester interfaces with a Ford's OBD II computer system and reads error codes stored within the computer module. The error code will tell the tester which coil pack is not working at optimum functionality. OBD II readers can be purchased from automotive parts retailers if you are confident in working with vehicles. Otherwise, an automotive repair facility should be contacted.
Inspecting the ignition coil housing for cracks is a great way to determine if a coil is underperforming. Any coil with a cracked housing should be replaced, because coils are exposed to constant heat when the vehicle is on. This can cause plastic housings to crack, allowing moisture into the coil pack. Electrical current and electricity do not blend together, and this can cause a short in the coil pack.