Why Do Spark Plugs Have Resistors – Best Guide

The intense sparks required to ignite the mixture of air and fuel are produced by spark plugs, which are crucial parts of a combustion engine. You might be perplexed as to why resistors are used in some spark plugs, though. Reduced electromagnetic interference (EMI) is the main motivation. High-frequency electrical noise produced by the spark plug during operation has the potential to disrupt nearby radio and electronic equipment. 

Why do spark plugs have resistors? The spark plug and ignition coil themselves both experience significant strain as a result of this quick energy release. A resistor is added to the circuit to absorb any voltage peaks and somewhat delay the current flow. This increases the longevity of these pricey components and guarantees more reliable performance over the course of their operating lives.

What is a resistor in a spark plug? 

By lowering electromagnetic interference (EMI) and extending the life of various engine components, a resistor found in a spark plug plays a significant part in how well an engine runs. Between the core electrode and the metal shell, this tiny but important part serves as a filter to muffle any electrical noise generated during the igniting process. This contributes to the continued proper working of the car’s electrical equipment, including the GPS and radios.

A resistor improves fuel efficiency and lowers hazardous emissions from the engine in addition to assisting with smooth radio reception. The resistor lessens the possibility that EMI will harm other electronic parts of your car. A spark plug with a built-in resistor is increasingly necessary for optimal performance as technology advances lead to more complicated automotive systems.

Benefits of resistors in spark plugs

Following are some benefits of resistors in a spark plug!

1. Fuel economy optimization: 

Spark plug resistors make a substantial contribution to increasing fuel efficiency. By delivering the exact amount of current needed for sparking without losing electricity through excessive heat or sparking energy loss, they make sure that energy is used efficiently. As a result, automobiles using spark plugs that have resistors can get better gas mileage and emit less pollution.

2. Longer life of the ignition coil: 

Increased ignition coil longevity is a benefit of employing spark plugs with built-in resistors. Coils are put under less strain over time because the electrical noise brought on by interference from unfiltered voltage spikes is decreased. For owners of vehicles, this means less frequent replacements and total cost savings.

3. Enhanced protection against radio frequency interference (RFI): 

In the technological age of today, where multiple electronic equipment coexist in automobiles, it is crucial to prevent any disruption brought on by RFI.

4. Increased Performance: 

The addition of resistors to spark plugs can significantly improve an engine’s performance. Reducing electromagnetic interference enables resistors to improve ignition timing and combustion efficiency. The engine is able to run more smoothly, generate more power, and have fewer misfires as a result.

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5. Noise Reduction: 

Resistors help to reduce the electrical noise that is produced during the ignition process. This lessens radio frequency interference that other electronic components in a vehicle experience, which not only serves to improve audio quality in cars with radios or onboard sound systems.

6. Improved Combustion Efficiency: 

This results in better fuel economy. Resistors aid in increasing the amount of fuel burned inside the cylinders by ensuring that each spark plug burns at the precise appropriate time without any outside interference. For any car using resistor-based spark plugs, this results in less fuel being used and better mpg.

7. Environmental Friendliness: 

Effective fuel use benefits the environment by lowering harmful emissions in addition to saving money. Spark plugs play a role in achieving cleaner exhaust gasses when used in conjunction with resistors because they help avoid incomplete combustion, which reduces the amount of greenhouse gas emissions and dangerous chemicals released into the atmosphere.

How many ohms should a resistor spark plug have?

The resistance of a spark plug is an important factor that can affect the performance of an engine. The general rule of thumb for the resistance of a resistor spark plug is between 5,000 and 10,000 ohms. This range helps to suppress radio frequency interference (RFI) while still allowing enough voltage to pass through for a strong spark.

However, it’s important to note that the specific recommended resistance for your vehicle can vary depending on factors such as engine size, make, and model. Consult your car’s owner’s manual or reach out to a trusted mechanic to determine the ideal resistor value for your spark plugs.

While there may be temptations to use non-resistor or low-resistance spark plugs, doing so can lead to adverse effects like decreased fuel efficiency and premature wear on electrical components. So make sure you choose the right resistor value for your spark plugs to keep your engine running optimally and reduce potential long-term damages.

How many types of resistive spark plugs

There are primarily two types that you may encounter – the resistor type and the suppressor type.

Resistor-Type Spark Plug

One of the key features of resistor-type spark plugs is their ability to reduce electromagnetic interference (EMI). This is crucial in modern vehicles that are equipped with various electronic systems, as excessive EMI can disrupt their functioning and lead to performance issues.

Suppressor-Type Spark Plugs

Suppressor-type spark plugs are a crucial component of an engine’s ignition system, ensuring optimal performance and reducing noise interference. One notable feature of these spark plugs is their ability to minimize radio frequency interference (RFI). By suppressing the electrical noise generated during fuel combustion, suppressor-type spark plugs prevent disruptions to nearby electronic systems such as radios and GPS devices.


Spark plugs have resistors for several important reasons. First and foremost, the resistor helps to reduce electromagnetic interference (EMI) generated by the ignition system. This interference can disrupt the operation of other electronic components in the vehicle, such as the radio or navigation system. Additionally, the resistor helps to prolong the lifespan of the spark plug by reducing wear and tear caused by excessive heat and voltage. 

Resistors help to ensure a consistent and reliable ignition process, resulting in improved fuel efficiency and engine performance. By understanding why spark plugs have resistors, car owners can make informed decisions when selecting new spark plugs for their vehicles, ultimately leading to a smoother and more efficient driving experience. 


1. Why do spark plugs have resistors?

Spark plugs have resistors to reduce electromagnetic interference (EMI) and radio frequency interference (RFI) which can affect the performance of various electronic components in a vehicle.

2. What is the purpose of reducing EMI and RFI?

Reducing EMI and RFI helps prevent disruptions in the operation of sensitive electronic devices such as radios, GPS systems, or engine control units (ECUs).

3. How do resistor-equipped spark plugs work?

Resistor-equipped spark plugs limit the amount of electrical energy flowing through the plug, which reduces EMI and RFI emissions while still allowing for efficient combustion in the engine.

4. Can I replace my vehicle’s resistor-equipped spark plugs with non-resistor ones?

It is generally recommended to stick with the type of spark plug specified by your vehicle manufacturer. If you want to switch from resistor-equipped to non-resistor spark plugs or vice versa, consult your vehicle’s manual or a trusted mechanic for guidance.

5. How often should I replace my resistor-equipped spark plugs?

The replacement interval for any type of spark plug varies depending on factors like driving conditions and manufacturer recommendations. Generally, it is advisable to replace them every 30,000-50,000 miles or as specified in your vehicle’s maintenance schedule.

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