Ford Repair Questions? Ask a Mechanic for Answers ASAP
Hi, I am a Expert certified mechanic, with an engineering background, and 35+ years experience. I will do my best to assist you. Also keep in mind I don't know if you are a pro or a novice, so feel free to add any additional info at any time. I am also an electrical specialist and I will try to help you with this problem. On an ignition coil that takes a coil out is too much power draw, vibration, or excessive heat (normally from over powering) Vibration is something pretty straight forward that you can confirm by inspecting the mounting. If it is bolted on firmly in the factory location it is pretty safe to assume that vibration isn't a factor. That leaves too much power. To understand this part you need to have a good idea of what controls the power draw of a coil. The power draw is determined by the electrical resistance of the coil measured in ohms. There is even a formula that you can use to determine the power draw. It is the Amperage = Voltage (divided by) the resistance (in ohms). It works like this, if the circuit has 2 ohms of resistance, and it is a 12 volt circuit that means that amps = 12 divided by 2, so 12/2=6 the circuit will draw 6 amps. So unless it is the wrong coil, or the voltage is increased the coil cant draw additional power, causing an overheat failure. This basic formula will carry you through a lot of electrical problems. So what do we have left that could be the problem. It's is important to understand that no matter what happens because of the characteristics of electricity that the coil cant be overloaded unless it is over volted. Even if you directly short the output it still has the same internal resistance, so the power draw is set in stone so to speak. So now I am wondering what the voltage is to the coil. If the system voltage is too high (above about 14.5 volts) the coil might draw excessive amperage possibly burning out coils. But there should be other signs of over voltage, battery failure, and other devices burning out. I would measure the voltage at the positive terminal of the coil and the positive battery cable with the engine running to see what the voltage is. What I have seen on Fords is, sometimes the wire will break inside the plastic right before the connector to the coil. If you unplug a coil that isn't working and plug back in a new coil it might work for a while. I have also seen the 12 volt electrical connector loose good connection to the actual wire at the coil, and cause symptoms like coil failure. These problems are hard to spot. I would consider installing a new connector for the coil and trying it. On the vehicles I have worked on this has solved a lot of problems. Go over all of this and if you have any more questions at all, I am here to help. Good luck with it, have a great day, and Thanks for using Just Answer. I do not get paid for my work unless you rate at 3 to 5 Smiley Faces or Stars, a bonus is always greatly appreciated. If the answer is not clear, let me know what additional help you need, and I will be happy to assist you further.