Bad Spark Plug|Spark Plug|Bike Spark Plug|Damaged Spark plug

We all want a smooth-running engine that performs at its optimum in all driving conditions. Of course, proper maintenance goes a long way in ensuring that your car will not let you down, but there are some things you can do for trouble-free driving. The spark plug is one component of the engine that is essential for its working. However, they do sometimes go bad, so, what are bad spark plug symptoms?

Spark plugs are used in all petrol engines in cars or motorcycles and are responsible for providing the spark that ignites the air-fuel mixture to provide the necessary power. This article looks at bad spark plug symptoms and what you can do to keep your engine running in good condition.

Identifying bad spark plug symptoms

Without spark plugs, the engine could not produce any power. The air-fuel mixture would not ignite, so timely maintenance of spark plugs keeps the engine going and provides you with a smoother driving experience.

Spark Plug

What causes bad spark plugs? The following are some bad spark plug symptoms that apply both to car and motorcycle petrol engines.

Also read Fuel System Cleaning: Clean the System Quickly

Starting trouble

Will bad spark plugs cause a car engine not to start? Definitely, when an engine doesn’t start after a few attempts, we may suspect the battery or the starter motor may be faulty.

But it is a good idea to check sparkplugs for carbon deposits. A faulty sparkplug will not allow the engine to turn over and you may struggle to get it started.

Engine knocking

How do I know if spark plugs in my engine need changing? When sparkplugs are in need of replacement, they will engine will start to idle roughly with the sparkplugs igniting the air-fuel mixture at the wrong time. At this point, you will hear knocking sounds from the engine, rattling, vibrations and hesitation while driving.

Also Checkout Why do car engines overheat and how to deal with them?

Unfamiliar, loud engine noise

What happens when a spark plug goes bad?  A bad spark plug will cause the piston to vibrate within the cylinder and cause loud, unfamiliar noises from the engine. The overall power output drops and you will hear unpleasant sounds from the engine as you drive. This indicates the cylinders are being overloaded and spark plugs have gone bad.

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Poor acceleration

If you have spark plug noise when accelerating, this usually indicates they need to be checked. Acceleration performance will drop drastically and you will constantly have to change gears to get enough power. Can bad spark plugs cause high rpm? Yes, the engine speed will vary due to defective spark plugs, so keep an eye open for sudden changes in rpm without any throttle input.

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Engine misfires

A bad spark plug sounds like a misfire when the air-fuel mixture does not combust and raw fuel is emitted from the exhaust. You may hear a pop and a drop in power as the engine struggles to maintain rpm due to the misfire.

Also Read The Parts of a Car Engine: A Comprehensive Overview

Poor fuel mileage

When spark plugs do not work effectively, they will require more fuel to provide the same power and you may find that fuel efficiency will take a hit. A bad spark plug will cause insufficient and inconsistent burning of the air-fuel mixture, and raw fuel may be emitted from the exhaust system. This is considered a waste of fuel because it has not been burned to produce power.

Also Checkout How to Increase Car Mileage Instantly

What are bad spark plug symptoms in motorcycles?

2 stroke bad spark plug symptoms are usually the same as with other vehicles including engine misfiring, loss in performance, inconsistent fuel mileage and trouble starting.

Bike Spark Plug

If you inspect a bad spark plug on a 2-stroke motorcycle, you will find black carbon deposits in the spark plug gap. They will also be oily residue on the spark plug which prevents it from firing effectively. This can be caused by an improper mixture of petrol/ oil or a carburettor that has been set to a rich mixture.

Also read The Difference Between A 2-stroke And 4-stroke Engines

How do you start a car with bad spark plugs?

In order to get your car started with bad spark plugs, you will have to remove them and clean the spark plug gap. Ensure that the gap is the at recommended value, and widening or reducing the gap is needed. Clean any oily residue and carbon deposits on the spark plug.

Damaged Spark plug

Inspect the spark plug high tension wires for any cracks or breaks. This may cause an insufficient voltage to be sent to the spark plugs resulting in a hard start.

Ensure the cylinder head is in good condition because a faulty cylinder head will result in incomplete combustion. There will not be enough compression in the cylinders and the bad spark plug will make starting even more difficult. The best solution is to replace bad spark plugs with new ones. This should eliminate any starting trouble.

Also Read What Are The Signs Of A Bad Starter? How Do You Identify That Your Starter Is Failing?


The spark plug is a simple engine component but is critical for the motor to function. Without a spark plug, the air-fuel mixture could not ignite, and no power would be produced within the combustion chamber.

It is not always easy to identify bad spark plug symptoms and not every driver knows what a loose spark plug sounds like. Hopefully, this article will give you a better idea of bad spark plug symptoms and ways to solve starting issues or rough idling.

If you found this article on bad spark symptoms informative, look at some other related articles such as How Do You Know When Your CV Axles Are Going Bad? and A Bad Battery Vs A Bad Alternator or visit Carorbis Blog for more article.

Frequently Asked Questions

Q1. What does an engine sound like with bad spark plugs?

Ans. If the spark plugs are not functioning properly, you will hear a knocking sound from the engine while accelerating. Engine knocking is caused by the spark plugs not producing sparks at the right time which prevents the air-fuel mixture from detonating in the combustion chamber. The fuel does not ignite and power is not produced in the cylinders, resulting in a distinctive knocking sound. The air-fuel mixture eventually ignites, but it may cause a loss of power in the engine. Replacing worn-out spark plugs with new ones is the best way to solve the issue of bad spark plugs and knocking.

Q2. What symptoms do bad spark plugs cause?

Ans. The engine needs an air-fuel mixture plus a spark from the spark plug to work properly. If a spark plug is bad and does not work as designed, it will have a number of symptoms that are easy to identify. Some symptoms that bad spark plugs cause are:

  • Engine misfire – the spark plugs fire at the wrong time, or they fail to create a spark which leads to a loss in engine power and potential damage to the piston and cylinders
  • Engine knocking – incomplete combustion of the air-fuel mixture due to bad spark plugs, causing a knocking sound from the engine followed by loss of power
  • Rough operation – the engine will not idle smoothly and there will be considerable vibrations from the cylinders due to bad spark plugs
  • Starting trouble – Bad spark plugs do not produce a strong spark which is needed to ignite the air-fuel mixture while starting, therefore the car will not start properly.

Q3. Can a bad spark plug make a ticking sound?

Ans. A car that has high mileage on its engines and has not had its spark plugs replaced may emit a ticking noise when accelerating or at high speed. The most likely cause of the ticking sound is damaged or malfunctioning spark plugs. The spark plug may not be in its correct position, may have been dislodged from its seat due to impact and so there is a gap in the housing. Exhaust gases may leak from this opening causing the ticking sound from the engine. Spark plugs need to be replaced every 100,000 km or sooner if they are exposed to severe driving conditions.

Q4. Why is my car making a rattling noise?

Ans. Rattling noises don’t usually come from bad spark plugs. It could be caused by a rusted or corroded exhaust system that has come loose or weak engine mounts.  Perhaps some engine component like the radiator or fuel injection system is making the rattling noise. In severe cases, the engine may be vibrating a lot due to bad spark plugs, but this will result in rough idling, knocking and ticking sounds. Eliminate the cause of rattles as soon as possible before it leads to expensive repairs down the line. Only symptoms like engine misfiring, knocking, rough idling and trouble starting should be considered as bad spark plug causes.

Q5. Why does my car make a rattling noise when I accelerate?

Ans. You may hear a rattling sound from the engine while accelerating also known as pinging or knocking. The noise is caused by the air-fuel mixture combusting before the spark plug ignites, or the spark plug firing at the wrong time. Sometimes the heat of the compression ignites the air-fuel mixture as the piston moves up the cylinder during the compression stroke. This may cause a rattling noise when accelerating and prevent smooth operation of the engine. Replacing the spark plugs is an easy fix and does not cost too much. It should solve the issue.

Q6. How do I know if my spark plug is misfiring?

Ans. In modern car engines, when the spark plugs misfire, a signal is sent to the onboard computer and ECU to flash a check engine warning light on the dashboard. On older generation cars, misfiring spark plugs may result in hesitation while accelerating, maintaining speed or climbing up a steep road. Fuel economy may also drop with misfiring spark plugs and you may find yourself refilling the fuel tank more often. Engine performance is sure to drop with a misfiring engine and you will have rough idling and poor response when stepping on the throttle. These are sure signs that your spark plugs are misfiring, due to being faulty or because of a problem with the ignition system/timing.

Q7. Is it hard to change spark plugs?

Ans. Changing spark plugs is a simple procedure and for a 4-cylinder, inline engine, the whole process should take less than an hour. It can be done in the comfort of your home garage with simple tools such as a spark plug wrench, spanners, insulating gloves, a can of WD40 and a set of new spark plugs (refer to the owner’s manual for the type, brand and size of spark plug your car uses). It will save you a lot of money rather than going to a mechanic and your engine performance and fuel mileage will increase drastically.

Q8. Will changing spark plugs fix a misfire?

Ans. A change of spark plugs will most likely fix a misfire in the engine. Spark plugs can be easily removed and replaced in an engine for around Rs.500 and can be bought at any car accessory store. Besides fixing a misfire in the engine, a new set of spark plugs will provide improvements in power delivery, torque, acceleration and fuel economy while reducing emissions. A misfire occurs with faulty spark plugs that do not produce a spark during the power stroke of the piston in the cylinder, thereby leading to a drop in engine performance and unburnt gases exiting the combustion chamber.

Q9. How often do spark plugs need to be replaced?

Ans. Spark plugs are durable components that are designed to work for up to 80,000 km without a replacement. If the car is driven in severe conditions like dusty roads, towing heavy loads, in stop-and-go traffic or at high speed for extended periods of time, then spark plugs may need replacement at around 50,000 km. In any case, it is best to check carbon build-up in the spark plug and adjust the gap at every service of the car. Keeping the spark plugs in good condition leads to better engine performance, smoother rides and good fuel economy.

Q10. Can bad spark plugs cause transmission problems?

Ans. Not directly, but when you have bad spark plugs, you will be using the transmission more often to maintain power and acceleration. Bad spark plugs can also cause high engine rpm which may affect an automatic transmission adversely.

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