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Symptoms of Bad or Failing Spark Plugs

failing spark plugs

Without spark, there would be no way for fuel to ignite in the combustion chamber. Spark plugs have been a critical component of the internal combustion motor for years. They are designed to transmit an electrical signal sent to the spark plug from the ignition coil and a predetermined time to ignite fuel inside the combustion chamber. Each vehicle requires a unique spark plug made from specific materials and with a designated spark plug gap that is set by a certified mechanic during installation. A good spark plug will help burn fuel efficiently while a bad spark plug can cause the motor not to start at all.

Spark plugs are similar to oil, fuel filters and air filters in that they require routine service and maintenance in order to keep your car running strong. Most vehicles sold in the US require that spark plugs are replaced every 30,000 to 50,000 miles. However, newer cars, trucks and SUV's manufactured have advanced ignition systems that claim to have lifetime warranties on the plugs. Regardless of the warranties, or claims made, there are times when a spark plug wears out or shows signs of failing.

Listed below are a few of the common symptoms of worn out spark plugs or spark plugs that have fouled and need to be replaced by a local ASE certified mechanic as soon as possible, so you can continue driving your vehicle without hassle.

1. Slow acceleration

The most common cause of poor acceleration on most cars, trucks and SUV's is a problem in the ignition system. Today's modern engines have multiple sensors that tell the on-board computer and ignition system when to send electric pulses to fire the spark plug. However, sometimes the issue is just as simple as a worn out spark plug. A spark plug is composed of materials that work together in order to produce a spark hot enough to ignite an air to fuel mixture. When those materials wear out, the effectiveness of the spark plug is reduced, which can significantly reduce the acceleration of the vehicle.

If you notice that your car is running sluggish or does not accelerate as quickly as it used to, it may be contributed to a spark plug that needs to be replaced. However, you should contact a mechanic to inspect this issue as it could be caused by multiple other factors including bad fuel filters, dirty or clogged fuel injector, or issues with O2 sensors.

2. Poor fuel economy

When a spark plug is working correctly, it helps to burn fuel efficiently. When this occurs, your car can achieve better than average fuel economy. When the plug is not burning efficiently, it is commonly due to the fact that the gap between the spark plug electrodes is either too close or too far apart. In fact, many mechanics will take out spark plugs, examine them and adjust the gap to factory settings during a routine tune up as opposed to replacing the spark plug. If your vehicle is losing fuel economy, it very well could be contributed to a worn out spark plug.

3. Engine is misfiring

If the engine misfires, it's typically due to an issue in the ignition system. Most of the time in modern cars, it's due to a sensor that is malfunctioning. However, it may also be caused by a spark plug wire or the tip of the spark plug that connects to the wire being damaged. An engine misfire can be noticed by intermittent stumbling or stuttering sounds from the engine. If the engine is allowed to keep misfiring, exhaust emissions will increase, engine power will decrease, and fuel economy will reduce.

Because of all the potential problems associated with engine misfiring issues, you should contact a mechanic as soon as you notice an engine misfire, so they can inspect the issue and determine the right course of action to repair the problem.

4. Difficulty starting the vehicle

If you have trouble starting your vehicle, it could be a sign your spark plugs are worn. However as we've noted above, the engine's ignition system is comprised of multiple individual components that must work cohesively in order to function properly. At the first sign of problems starting your car, truck or SUV, it's a good idea to contact the mechanic, or contact one of our mechanics at to ask a free question.

Regardless of what the issue might be, the reality is that spark plugs will eventually wear out. Being proactive about spark plug maintenance can extend the life of your engine by hundreds of thousands of miles.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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