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How Long Can You Drive with Bad Spark Plugs?

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Is your car sending you smoke signals with rough idling and mysterious misfires?
Well, it’s probably time to switch out your spark plugs.

Now, you’re left wondering how long can you drive with bad spark plugs
Or how much does a replacement cost? 

Read on to find the answers to these and more questions, like signs of failing spark plugs and how to extend the life of your spark plugs.

This Article Contains:

How Long Can You Drive with Bad Spark Plugs?

If your spark plugs are just starting to go bad, you may be able to drive for 500-1000 miles before coming to a stop. It depends on the exact condition of your spark plugs.

To avoid such situations, most vehicle manuals recommend replacing standard spark plugs every 30,000 to 40,000 miles. 

Not replacing them in time can decrease fuel efficiency, cause engine misfires, and, in extreme cases, even damage your engine and other important parts like a catalytic converter.

But not if you spot the warning signs of a bad plug first.

6 Prominent Signs of Bad Spark Plugs 

From a misfiring engine and increased fuel consumption to sluggish acceleration, here are some tell-tale signs you should keep an eye out for:

1. Difficulty Starting Your Car

A car that stalls during startup might indicate issues with the spark plug or spark plug wire. For instance, your vehicle may take more attempts than usual to start or require holding the key in the start position for longer.

This happens when worn spark plugs struggle to ignite the spark needed to power your engine.

Note: If your car completely lacks power or you hear clicking sounds when starting, you may have a starter or battery problem.

2. Engine Misfire

When spark plugs are worn out, corroded, or covered in deposits, they may produce a weak spark that can’t ignite the fuel properly — leading to an engine misfire.

But that’s not all.

The gap between the electrodes in a spark plug can widen over time, further weakening the spark or not firing it at the right time. This causes misfires at high speeds and can even trigger the check engine light.

Note: Misfires also happen due to other ignition system issues (like ignition coil pack troubles), faulty emission equipment, control circuit module problems, and more.

3. Sluggish Acceleration

Due to incomplete combustion and decreased engine power, you may notice that your car isn’t responding well, especially when you’re trying to accelerate.

However, a clogged fuel or air filter, a faulty catalytic converter, or transmission issues can also cause trouble when accelerating.

4. A Lit Check Engine Light

The ECU tracks the engine’s performance and emissions system through sensors.

If the sensors detect irregularities caused by faulty spark plugs, like engine misfires, the ECU interprets these as issues that could affect the engine’s performance or emissions. As a result, it triggers the check engine light as a warning to the driver that the engine needs attention.

Apart from failed spark plugs, bad ignition coil packs and spark plug wires can also trigger your check engine light to come on. 

5. Rough Idling

Ideally, your engine should purr like a kitten.

But if you have worn spark plugs, you may experience noticeable vibrations throughout your vehicle, along with rattling or knocking noises. If left untreated, rough idling can damage sensitive parts like engine mounts and exhaust manifolds.

6. Decreased Fuel Economy

When the ECU detects incomplete combustion, it tries to compensate by enriching the air-fuel mixture — it adds more fuel to ensure optimal engine performance.

However, this often leads to unburned fuel exiting through the exhaust, increasing fuel consumption without contributing to engine performance. So, if you notice an increased gas mileage, it’s probably a good idea to have your spark plugs looked at.

Next, let’s find out why you have a faulty spark plug.

What Are the Causes of a Bad Spark Plug?

Here are a few reasons why your spark plugs go bad:

  1. Carbon buildup: Debris buildup around the tip of the spark plug can lead to failing spark plugs, hard starts, and misfires. This can be due to a dirty fuel injector, driving at low speeds, or excessive idling.
  1. A worn electrode: The repeat ignition of air-fuel mixture in the combustion chamber can wear out the electrodes. A bad electrode leads to a defective spark plug, disrupts combustion, and causes engine damage.
  1. Improper spark plug gap: The gap between a spark plug’s electrodes must be precise for optimal engine performance and proper fuel ignition. If this gap isn’t set correctly, it can strain the spark plug tip and lead to premature wear.
  1. Overheating: Overheating happens due to issues like pre-ignition, where heat piles up in the combustion chamber and causes spark plug failure. Cooling system issues can also overheat the engine and spark plugs, leading to premature wear of the electrodes. 

No matter the cause, get a new spark plug at the first sign of trouble.
But how much are they going to cost?

How Much Does a Spark Plug Replacement Cost?

Spark plug replacement costs vary based on the type of spark plugs, vehicle model, and labor charges in your region.

Here are some estimated costs of different plug types:

The average labor cost ranges between $40 – $350. 
Considering these costs, the cheapest spark plug replacement can cost between $100 – $250, and the highest is about $250 – $500.

Wondering how you can extend your spark plug’s life and avoid costly repairs?
Let’s find out.

6 Handy Tips to Maintain Healthy Spark Plugs

Here are some tips to ensure your spark plugs last long:  

  1. Follow routine spark plug maintenance and replacement intervals suggested in your vehicle’s manual.
  1. Use the type of spark plug recommended by your vehicle’s manufacturer.
  1. Use high-quality fuel to reduce the residue accumulating on your spark plugs.
  1. Ensure the spark plug wire is in good condition and securely connected, as damaged wires can affect spark plug performance.
  1. Practice gentle driving to make your spark plugs last longer. Aggressive driving can wear out spark plugs and other engine parts, like catalytic converter, faster.
  1. Clean the area around the central electrode with a plug cleaner to remove any debris, like porcelain dust. Remember to keep the plug facing down while you spray the cavity.

Get Hassle-Free Spark Plug Replacements at AutoNation Mobile Service

Driving with faulty spark plugs can lead to reduced engine power, poor fuel combustion, significant engine damage, and costly repairs.

However, spotting and replacing spark plugs on your can be difficult. And that’s why you should take the help of an expert mechanic or auto repair center like AutoNation Mobile Service.

We’re a mobile auto repair and maintenance service available seven days a week. We offer upfront pricing, convenient online booking, and a 12-month, 12,000-mile warranty on all repairs.

Get in touch with us and we’ll come fix your car right in your driveway.