Bad Spark Plug Signs – Diagnose Faulty Spark Plug Symptoms Like a Pro

In this post, we’d like you to tell you some basics behind the spark plugs, focusing specifically on what the bad spark plug signs are.  This is to help you, our dear reader, recognize bad symptoms early and avoid potential damages. Let’s start with a bit of basics.

Bad Spark Plug Signs – The Basics, in a Nutshell

The spark plug got its so-called name because it springs your car to life by making a spark in the combustion chamber to ignite fuel. This leads to a series of reactions and sets your car’s pistons in motion giving your car power.

bad spark plug signsThis process repeats and each engine cycle requires the spark plug to reignite. If the spark plug is not able to do so, the engine will misfire and could potentially cause damage.

For something tiny, it has a mighty role in keeping your vehicle working at its best so it is crucial to keep its health in check and know the common bad spark plug symptoms.

We have rounded up signs that could indicate that your spark plug could be screaming to be replaced.

While they could be symptoms of other failures too, these are the common ones that you can easily spot and the ones that your mechanic would be very familiar with.


Bad Spark Plug Symptoms – Recognize Them Early

  1. It is hard to get the engine started.

    A spark plug is one of the key components of a vehicle’s ignition system along with the ignition coils. A faulty spark plug does not provide enough spark to start the engine which causes the engine to stall and fail to start.

    If this goes unchecked, apart from hurting the entire ignition system, a bad spark plug could eventually cost you the battery too.

  2. Your car does not accelerate quickly.

    If the spark plug is not in tip-top condition, the vehicle may not accelerate as fast and as quick as it used to when you step on the gas.

    It would not generate a spark that is hot enough to ignite the fuel-air mixture and therefore won’t be as effective in revving up your vehicle.

  3. The check engine light is on or flashing.

    check engine light spark plugs problemsThere is a myriad of things that would bring on a check engine light, ranging from a loose fuel cap to a dead battery.

    A failing spark plug is one of the common culprits that summons the distressing check engine light.

    With a bad spark plug specifically, your vehicle would not be able to seal the combustion chamber and provide the needed gap for a spark to start combustion in your engine.

  4. The engine misfires.

    You would usually feel a jolt or hesitation in delivering power to your vehicle’s acceleration. A spark plug needs to constantly maintain the ignition of the fuel-air mixture.

    When a worn spark plug fails to do so, it would cause a halt in the running of your engine. This could also discard fuel into the exhaust and damage the catalytic converter.

  5. There is increased emission from your vehicle (and it smells too).

    faulty spark plug emissionOnce the unburnt fuel that is forced by the misfiring spark plug finds its way to the exhaust system, it sets the catalytic converter to a very high temperature and the unburnt fuel ignites in the converter which could cause a meltdown of the catalyst.

    A happy catalytic converter is supposed to convert hydrogen sulfide created from sulfur-containing gasoline during combustion to odorless sulfur oxide.

    A catalytic converter that has gone bad would not be able to do this job resulting in a sulfuric smell (kind of like rotten eggs) from the exhaust and dark smoke could also be emitted by the exhaust.

  6. You have been gassing up your vehicle more than ever before.

    And it is not because you’ve been traveling more.

    A perfectly working spark plug will leave no residue because it will create just the right amount of spark for complete combustion. A worn one does otherwise, which depletes your vehicle’s fuel at a much faster rate.

    The cost of frequent refueling should be more than enough reason to have the trip to your mechanic.

  7. Your car is idling roughly.

    If you feel rough vibration throughout your vehicle while it is stationary, a bad spark plug may be to blame. Ideally, when a vehicle is idle, the engine should run at a low RPM.

    That bouncing sensation may be caused by the vehicle’s electronic control unit trying to make up for what the spark plug is not able to efficiently perform and that is to help burn fuel at a consistent rate.

  8. The tailpipe produces a loud pop or a coughing or sputtering sound.

    While this could be frightening, the sound itself is unlikely to cause harm but it is not part of the vehicle’s normal operation and should be avoided.

    The engine’s backfire could be caused by a spark plug that is not generating the required spark when the exhaust valve opens. If the fuel-air mixture becomes too rich, unburnt fuel stays in the exhaust system. The offending spark plug then ignites the rich fuel-air mixture, producing that loud bang.

  9. You hear rattling, knocking, and pinging.

    This is called engine knocking. If the fuel-air mixture does not burn cleanly, it gets pressed against the piston and the cylinder wall which generates intense heat and pressure.

    This mixture then ignites itself and makes that knocking or pinging sound.


What Wears Spark Plugs Down? When to Change Spark Plugs?

when to change spark plugsSpark plugs are designed to be disposable but fortunately, you can go without having to replace them for years and your vehicle would have already traveled miles and miles by then.

The following are the common factors that affect the longevity and ultimately determine when to change the spark plugs.

Some are part of the eventual wear and tear, while the spark plug problems caused by the other factors can be reduced or preempted with proper care.

  • Oil contamination.

    The oil will make its way to the combustion chamber over time as the seal weakens and could damage the tip.

  • Increasing gap.

    There has to be a perfect gap of space when a spark plug ignites to give just the right combustion at the right moment. This gap widens the older the spark plug gets due to debris, intense temperatures, and use and abuse. If the gap is too wide, the combustion will not be as effective as it used to be.

  • Deposit Buildup.

    Buildup happens when air filters, injectors, among other things, are not cleaned and maintained.

  • Overheating.

    Electrodes could break down faster due to overheating. If there is pre-ignition from a badly timed engine, overheating can happen. Correct air to fuel ratio must also be ensured to prevent overheating.


Bad Spark Plug Signs / Symptoms – What to Do When You Confirm Them

If your car is exhibiting some of the bad spark plug signs and symptoms mentioned above, it is best to seek your trusted mechanic for advice.

While some symptoms may not be a cause of alarm right now, they may result in other issues that may be more costly to fix the longer we leave it for another day.

Also, check with your spark plug’s manufacturer to know how long they will last for. Good spark plugs usually last around 60,000 to 70,000 miles but that can vary based on the conditions that the vehicle has been exposed to.

It is always best to err on the side of caution and replace the spark plugs before they can present problems.

And you can always check with us here at the Garage Chief, for additional help and advice on not just spark plugs but overall vehicle care!

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