Spark Plug Problems – Function – Failure Symptoms – Replacement

Spark Plug Problems - Function - Failure Symptoms - Replacement
Spark Plug Problems - Function - Failure Symptoms - Replacement

All spark plugs wear out as they age and at some point, will cause spark plug problems.

Because, after enduring abuse for thousands of miles, you really can’t expect them, to last forever.

Good spark plugs, will burn fuel efficiently. While, bad or failing spark plugs, can cause a number of spark plug problems.

So, with most spark plug problems, the first thing to happen, is reduced spark or no spark at all.

And, without a proper spark, there would be no way, for fuel to ignite in the combustion chamber. Consequently, all spark plugs require routine service and maintenance, to keep your engine running strong.

Normal Spark Plugs

Usually, your vehicle can go for years and several miles, before you have to worry about, getting new spark plugs. Spark plugs have been, a critical part of the internal combustion engine, for years.

Spark Plugs, Have Two Primary Functions:

  1. Electric energy from the ignition coil, is transmitted through the spark plug. Then, it jumps the gap, creating an electric spark. Finally, this electric spark, ignites the air to fuel mixture, in the combustion chamber.
  2. Spark plugs also, remove heat from the combustion chamber. But, spark plugs cannot create heat, they can only remove heat. The temperature of the end of the plug’s firing end, must be kept low enough, to prevent pre-ignition. But, high enough, to prevent fouling. The spark plug works as a heat exchanger, by pulling unwanted thermal energy from the combustion chamber. As a result, transferring heat, to the engines cooling system.

Common Spark Plug, Failure Symptoms

Most spark plug problems happen, because of deposits, from the combustion process. The deposits that form on the spark plugs, can result in pre-ignition of the fuel. This translates to, an unreliable supply of energy, for your vehicle.

Carbon Deposits
Carbon Deposits On Spark Plugs

Other reasons why spark plugs, can’t last for a really long time, is their exposure to:

Spark Plug Damage

These things, increase the gap or space, where the spark has to travel. First, the spark plug is a major part, of the ignition system. Because, it keeps the engine running, by constantly igniting, the air to fuel mixture.

Engine Misfire

So, the engine will appear to stumble, for a brief period of time and then regain its pace. And, this is most noticeable when accelerating or when the engine is in idle. Also, failing spark plugs, can cause the engine to misfire and thus affect engine performance.

Spark Plugs Causing Engine Misfire
Spark Plugs Causing Engine Misfire

Misfiring will cause, added exhaust emissions, reduced fuel economy and reduced engine power. A single misfire, can dump enough raw fuel into the exhaust, to overheat and damage the catalytic converter.

Excessive Fuel Consumption

Spark plug problems, might cause your engine, to consume more fuel than usual. As the (ECM) has no control over spark strength or oxygen content, it adds fuel to compensate for poor combustion. A properly working spark plug, helps to ensure the emissions from your vehicle, are kept at a minimum.

Deteriorated spark plugs, can lower your fuel economy, due to incomplete combustion. As your spark plug wears, the gap between the plug electrodes can either, expand or close up. Either of these conditions, can negatively affect your fuel economy and emissions.

Poor Acceleration

On acceleration, spark plugs are under particular demand, to deliver a strong spark. Also, to ignite more fuel and increase power. Faulty spark plugs or weak ignition coils, may not keep up with the demand. Examples of poor acceleration include, a lack of responsiveness or delayed reaction, when you press your gas pedal. In this situation, pushing down on the gas pedal, does not immediately boost the speed of the vehicle. Also, it will appear like, the engine is being overworked.

Rough Engine Idle

At idle, spark plug problems, might be evident as more of a vibration. Uneven idling and vibrations, are a major warning sign that indicates faulty spark plugs. Failing spark plugs can result in, the engine running rougher and producing vibrations, when left at idle speeds.

Spark Plugs Causing Rough Engine Idle
Spark Plugs Causing Rough Engine Idle

An engine with properly working spark plugs, should sound continuous and smooth. If your spark plugs are not working as they should, your engine will produce a rough and jittery sound. And, your engine will seem to stumble.

Hard Starting

Faulty spark plugs, can cause the vehicle to exhibit starting troubles. Worn out plugs, do not produce sufficient spark, which is needed for starting the engine. This results in engine stalling and will fail to start quickly. In addition, failing spark plugs, will also take its toll, on the battery life.

And, normal working ignition system. Proper ignition is most difficult, when the engine is “cold.” The (ECM) adds more fuel, to account for poor vaporization. And, that will make it difficult, for a worn spark plug to ignite. Resulting in hard starting, long cranking, or a engine no-start condition.

Check Engine Light

For many people, the check engine light, might be the only sign, your engine is having spark plug problems. The (ECM) is far more sensitive than many drivers think. Because, it can detect, a single cylinder misfire. If you get a check engine light along with slight jolts while accelerating, the spark plugs could be to blame.

Always check to condition, of the old spark plugs first. Because, they will show you, what was happening in your engine and other warning signs. I like to call them, the window into your cylinder.

How Do You Pick, The Correct Spark Plug For Your Engine

One of the most common problems vehicle owners experience, is knowing what spark plug to buy. Because, there are just so many brands to pick from.

The obvious solution is, to check your vehicle’s manufacturer and see what type they recommend. The manufacturer knows best, what your engine needs and what spark plug can meet those needs exactly.

Basic Spark Plug Replacement

Common Spark Plug Replacement Tools
Common Spark Plug Replacement Tools

Depending on the vehicle, engine, and spark plug type, spark plugs generally last, from 30,000 to 120,000 miles. For most vehicles, replacing spark plugs, is a simple job. All though you might need to be a contortionist, to get to some of them. Because, they might be placed, behind shields or under intake manifolds and other equipment.

Here Are The Basic Steps, To Replace Spark Plugs:

First, Get Access To The Spark Plugs

This might require, removing other parts, such as engine covers, heat shields, or the intake manifold.

Remove The Spark Plug Wires And Or Ignition Coils

Before removing wires, use tape or some other means, to mark their correct locations. Replace scuffed, worn, or damaged spark plugs wires or boots.

Use Compressed Air, To Blow Out Spark Plug Holes

Debris tends to collect, in unprotected spark plug tubes and channels. Using compressed air, is a good way to get rid of it. Also, preventing it from falling into the cylinder, when you remove the spark plug.

Remove The Spark Plugs

Using a spark plug socket, remove the old spark plugs. Inspect the old spark plugs. They can give you an idea, of what may be happening, inside your engine.

Recheck The New Spark Plug Gap

Most new spark plug gaps, are preset from the factory. But, it’s a good idea to check and adjust the spark plug gap, just to be sure.

Lubricate New Spark Plug Threads

Using just a dab of anti-seize lubricant, silver or copper doesn’t matter, lubricate the spark plug threads and gasket.

Install The New Spark Plugs

New Spark Plugs
New Spark Plugs

Turn the new spark plug in, by hand until finger tight, then torque to specs. Gasket types, usually specify a quarter- to a half-turn after contact. While, non-gasket types, specify just a sixteenth-turn. Check the manual to be sure.

Reinstall Everything Else

Finally, reinstall wires, coils and all other parts. Such as engine covers, heat shields, or the intake manifold. Being observant, is key to keeping a reliable engine. And, recognizing spark plug problems early, can improve fuel economy and prevent you from, being stranded.

Engine Ready To Go
Engine Ready To Go


So, knowing what happens, when spark plugs go bad, is essential to knowing, when to get replacements. Because, the signs of bad spark plug, are pretty obvious. Consequently, you should recognize these signs of a bad spark plug as soon as they appear. Finally, by being proactive about spark plug maintenance, you can extend the life of your engine, by thousands of miles.

Thank You !