If your gas-powered vehicle’s acceleration has gone from “zoom, zoom” to “putt, putt,” there’s probably a spark plug problem. Poor fuel economy is another indication the plugs or spark plug wires likely need replacing.

Although modern spark plugs last considerably longer than those produced 30 years ago, they don’t last forever and need to be replaced at regular intervals. It’s best to check the owner’s manual.

How Do I Know If My Spark Plugs Need Replacing?

ByRick Kranz 03/02/2022 4:00pm

What Does a Spark Plug Do?

A spark plug is screwed into each engine cylinder; it is needed to start the engine and keep it running. The biggest demand on an ignition system is to start the car and make it run. The portion of the plug that sticks out from the engine is connected to the vehicle’s ignition system, which must provide a specific amount of electric current to generate a spark inside each of the engine’s cylinders. The opposite end of the spark plug has two exposed electrodes that are located inside the cylinder. The electrical current from the ignition system travels to the plug’s center electrode. A high-voltage spark jumps a small gap to reach the second electrode.

That spark ignites the fuel-air mixture inside the engine cylinder. Each time a spark is created, a small explosion occurs inside the cylinder that pushes down against the top of the piston. If your vehicle has four cylinders, it has four pistons; six cylinders, six pistons, etc. each served by an individual plug.

The spark plug is a reliable workhorse. For example, at idle, say 800 rpm, the spark will fire 200 times per minute in a 4-cylinder 2.0-liter engine. As engine speed increases, say to 2,000 rpm, the plug fires 500 times per minute.

Types of Spark Plugs

As you probably know, different gas-powered cars boast different engines — which means they need different types of spark plugs. Depending on the number of cylinders your engine has will determine how many you need. It’s one for one. For example, if you drive a 4-cylinder engine, you need 4 spark plugs.

To go along with engine fit, most spark plugs get made from different types of metal, some being cheaper than others. However, cheap ones tend to last a shorter lifespan than ones made from more expensive metals. Manufacturers will typically recommend the type of spark plugs your gas-powered vehicle needs. It’s best to check your owner’s manual.

Get to know the types below.

Copper Spark Plugs 

Copper spark plugs, around for decades, are the most common and cheapest on the market. However, these tend to have a short lifespan, so you will need to replace them more often. 

Iridium Spark Plugs 

Iridium spark plugs offer a very long lifespan, which is reflected in the price. They are often the most expensive spark plug type on the market today. So, if your manual says you need iridium spark plugs, that’s what you need, because anything less might affect performance. 

Platinum Spark Plugs 

Platinum spark plugs last longer and typically run hotter. That means these spark plugs reduce carbon buildup in your engine. Since these are made with hard but high-quality metal, you can drive about 100,000 miles before needing to replace platinum spark plugs. If you drive a newer gas-powered car, some manufacturers will recommend this type.

Double Platinum Spark Plugs 

Double platinum spark plugs got their name not from a double coating, but because they are platinum on both the center electrode and the side electrode. These were made specifically for cars with “wasted spark ignition systems,” meaning two spark plugs are fired at once. This causes increased wear and tear on the spark plugs, which is why this type is necessary. You can use a regular platinum spark plug in a wasted spark system, but it will impact both performance and longevity. This type of spark plug also costs more. 

Silver Spark Plug Systems 

Silver spark plugs use silver at the electrode tip. These are pretty uncommon and are typically found in older European performance cars and motorcycles. Nonetheless, they are around but are often less durable than platinum and iridium spark plugs. Your vehicle will most likely not need these, but always double-check the manual. 

8 Signs the Spark Plugs or Spark Plug Wires Need Replacing:

1. Regular Maintenance

Check the owner’s manual for the replacement interval. Some automakers require a change at 18,000 miles, some at 30,000 to 35,000 miles, and others at 100,000.

2. Spark Plug Wires

Really old vehicles use a distributor, distributor cap, and spark plug wires. Some later models have an ignition system without a distributor, but they still have traditional spark plug wires. Newer vehicles use a coil-on-plug ignition system that eliminates electrical problems caused by worn-out spark plug wires. The industry now requires a more accurate control of spark and fuel delivery because of the need to annually boost fuel economy and reduce emissions.

Owners of older vehicles with spark plug wires may need to replace them because they become brittle and tend to crack. At that point, they are no longer providing the proper amount of electrical current to ignite the spark plugs and adequately burn the gasoline.

3. Fuel Economy Degradation

Dirty or fouled spark plugs reduce fuel economy because the plugs are not efficiently burning gasoline in the combustion cycle. Miles-per-gallon can drop by as much as 20% to 30%. A mechanic will replace the plugs and adjust each plug’s gap to factory specifications using a special tool.

4. Slower Acceleration

If it takes longer to accelerate, there’s less power to pass a car, for example, the issue could be worn spark plugs, they need replacing. However, a bad fuel filter, dirty or clogged fuel injectors, as well as issues with the oxygen sensor and ignition system can slow acceleration.

5. Rough Idling

If the engine is making a pinging, rattling, or knock-like noise, or if there is a strong vibration, the spark plugs and/or the spark plug wires could be to blame.

6. Engine Misfires

Replace the plugs more frequently if there’s oil on the plug’s tip when removed from the engine. The presence of oil is due to a cracked valve cover gasket, degradation of the spark plug O-ring, a faulty head gasket, or defective or worn valve guides. A repair is necessary because oil can cause the engine to misfire or prevent it from starting. An engine that continues to misfire could damage the catalytic converter, which might cost $1,000 or more to replace.

7. Difficulty Starting

Worn-out spark plugs can be the cause. Have a seasoned mechanic determine if the plugs need replacing. Simply, the engine will not start if the spark plugs can’t produce enough spark to start the combustion process. Some of the other causes for difficulty starting include issues with the ignition system, a battery needs replacing, or worn-out spark plug wires. Replace the car battery if it fails to produce enough voltage to start the engine.

8. Warning Lights

Finally, don’t ignore the “Check Engine,” “Malfunction,” or engine silhouette symbols. These warning lights may illuminate if the spark plugs fail, or if the spark plug wires need replacement. However, it depends on the automaker’s purpose for the light. It might be limited to warning the gas cap is loose, the vehicle is emitting emissions above U.S. regulations, the oxygen sensor or the mass airflow sensor may need replacing, and/or the catalytic converter is not operating properly.

One last reminder: If one of the lights mentioned above flashes, immediately shut off the engine and call a tow truck. The flashing light may signal a serious problem with the catalytic converter. Ignoring this warning could result in an expensive repair bill. Check the owner’s manual to know all the warning symbols for your vehicle.

If you prefer not to do the work yourself, you can check the average price for spark plug replacement for your vehicle, plus find a nearby auto shop to perform the service for you using Kelley Blue Book’s Service and Repair Guide.

River City Fleet Services can help you check and replace your spark plugs if needed.