Misfiring Spark Plug Common Causes and Symptoms

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misfiring spark plug

Most people think that misfiring spark plug is the main issue, while it’s actually a symptom – of another issue that may affect the performance of your car. When people are talking about misfires, they would immediately think about spark plugs. In reality, though, there are actually a lot of elements causing the misfire.


The Truth about Misfiring Spark Plug

As it was mentioned before, spark plug misfire isn’t the main cause of the issue. It’s merely misfire symptoms of other problems. In most cases, people think that replacing the spark plug would deal with the issue for once and for all. But if you haven’t found the root cause, the problem will return because you haven’t addressed the main culprit. Misfire can be caused by overall engine condition, emission system, fuel system, and ignition system.


How the Ignition System Works

The ignition system includes rotor, distributor cap, spark plug wire set, distributor, coil on plug boot, and coil. If any of these components fail, misfire may happen. A worn set of wires may cause voltage to ‘leak’ before it reaches the spark plug. As a result, it may have a no-spark condition or even a misfire. Exceeded spark plugs can also contribute to the misfire because they have gone past the recommended (service) interval and they have experienced expanded gaps.


Problems in fuel system can lead to lean or rich condition, which would contribute to the misfire. Often times, the main culprit is poorly tuned carburetors or clogged (and leaky) fuel injectors. Engines that are commonly used only once in a while (often times for seasonal usages), like snow blowers or lawnmowers, frequently experience varnish build-up, especially if you don’t follow the proper fuel storage system. Regular fuel filters replacement help to prevent this problem on the fuel system.


Further Possible Cause

The emission system (especially the sensors for oxygen) is responsible for providing feedback to the car’s ECU. This can either weaken or strengthen fuel delivery. If the sensor fails or it doesn’t properly communicate with the ECU, the car would turn to open loop operation, which means that it automatically defaults to a safer (and more efficient) rich fuel condition. If it happens for a prolonged time, not only it would waste the fuel, but it may damage the catalytic converters. Fuel fouled spark plugs may likely happen too.



If you believe that there is something wrong with your car, but you can’t really figure out what it is, it’s better that you take it to a trusted repair facility and have it checked. Don’t underestimate misfiring spark plug as it can cause long run headaches and financial issue.

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