how to find the bad coil

unplug them one at a time, if the motor stops missfiring, you have found the bad coil

A code reader will tell you which cylinder has the misfire. If you dont have a reader,With the engine OFF,disconnect one coil.Start the car If it runs worse,the coil you disconnected is good and not the problem. Try the other coils the same way.One at a time,with the car OFF when touching them. Eventually you will disconnect one,start the car,and it will run the same as when all are hooked up. This shows that this is the bad coil,as it is not contributing to the engines running. Note: Car may not want to start with a coil off.It is actually trying to run on 4 cylinders.The bad coil and the one you disconnected arent firing. This is comman with Ford Products,and many other newer cars.