Bad Ignition Coil Symptoms

Notice bad ignition coil symptoms before they start to affect your engine. An ignition coil that is in the first stages of failing will usually produce a steady but low voltage spark. When this happens, the flame in the combustion process is weaker, resulting in a lower percentage of the fuel being ignited during the period that it is in the cylinder during the compression and power stroke.

This situation will introduce more unburned fuel into the exhaust system. This will be recognized by the computer in response to the free oxygen within the exhaust system signaled by the oxygen sensor. In response to this signal being out of parameters, the computer will lean the mixture to prevent damage to the converter and illuminate the check engine light.

Fuel economy will suffer and black smoke and fuel smell will be ejected from the exhaust. Generally the idle will suffer and the engine will become harder to start. This will also tend to foul the spark plugs, which will rapidly induce a misfire.

In most cases, the reason for coil failure is overheating due to resistance in the secondary circuits, including the distributor cap, rotor, coil wire, ignition wires or spark plug gap. It is interesting to note that the mixture can cause resistance as well. The reason for this is that fuel is conductive. A good fuel mixture requires less voltage and amperage to jump the gap in the spark plug. The lack of fuel, as in a lean mixture condition requires much more power to jump the gap, hence increasing the temperature of the coil.

In many cases the coil has the tendency to quit working and fail once it reaches a certain temperature. It may work for several hours, depending on outside temperature and other contributing factors already mentioned before failing. Once the coil has failed, it may take an hour or more to cool before service is once again restored. This will make the car impossible to start.

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