Q: Got a question about one of my coils misfiring

asked by on June 07, 2017

Having a issue with a coil misfiring in my king ranch Ford Expedition, my local mechanic replaced one of my coils when my engine light was on. He got it replaced for me and a month or two down the line my light came on again. I took it back to him and he said he was nervous of trying to remove the spark plug because he thought it might break off and get stuck in there he referred me to a dealer, and that is where I am at right now contacting you for your opinion.
My car has an automatic transmission.

Ignition coils are coated with a varnish-like insulation that becomes brittle over time after being stretched then contracted repeatedly. The insulation develops small fractures that open when heated and close when cooled. When open, they allow shorting of coil windings and decrease or eliminate the coil’s ability to function. This type of temperature cycling happens because every time you shut the engine off, the fan stops running, the coolant stops flowing and the temperature under the hood rises. Every time you start the engine again the coolant flows, the fans turn on, and the temperature drops. When this heat dissipates and is absorbed under the hood, it is trapped causing this cycling effect. Other components that contain heat sensitive materials include parts like fuel injectors, igniters, and some sensors. Any of these may be potentially subject to this same kind of heat cycling problem which can be very difficult to trace. I would recommend having an expert from YourMechanic come to your location to take a look at your vehicle.

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