Bad Spark Plugs Symptoms and Replacement Cost

Bad Spark plugs Symptoms

The constant jiggering and frequent breakdowns of your car have led you to this very situation. you are going to know how to locate the bad spark plugs symptoms, layer yourself in those professional mechanic coveralls, and eradicate it.

A spark plug is one of the tiniest yet, most incremental parts of a vehicle. It is known to fire up the internal combustion engine. Little did you know that this, too, can cause so much havoc.

You must be wondering, "How do I know if my spark plugs are bad?".

Well, you can relax and just read through to know the basic symptoms and signs of bad spark plugs. As soon as you pay attention to the list below, you will know how to diagnose spark plugs, how to fix it for the smoothest drive ever and the replacement cost.


Symptoms of Bad or Failing Spark Plugs:

1. Poor acceleration

Suffering from poor acceleration? It’s my nightmare. However, the cause of slow acceleration can be a sign of the ignition system. When failing spark plugs don’t produce enough hot sparks to ignite the fuel mixture, it’s a sign of worn spark plugs, thus reduced effectivity.

If you’ve driven at your desired speed, whether that be 100mph or 60, you would be quick to assess the change. Sudden sluggish performance at speed is a bad spark plug symptom.

2. Gas Mileage

Are you spending more on gas now than the previous months? Frequent trips to the gas station can only be traced back to failing spark plugs. The combustion cycle is efficiently completed as the spark plug burns fuel at a respectable speed. But what if it halts all of a sudden?

It can only mean that there’s a gap in the spark plug functioning and delivering optimum results. Another conclusion drawn from such scenarios is the distance inconsistency between the electrodes.

3. Face difficulties in starting the Vehicle

Don’t you hate it when you face difficulties in starting your car? Even though you’re frustrated, you must think more in-depth into the cause. The underlying question is, ‘will a car start with bad spark plugs?’

The closest answer to that is no, and even if they do, it will be a stubborn process. Although a dead battery or the gas tank limits are viable reasons, sometimes they’re not the cause. An inactive spark plug will not let you reach your destination at peace.

4. Misfiring

Misfiring is a common phenomenon contributed by the notorious faulty spark plugs. The combustion cycle hesitates, causing interval in running your vehicle smoothly, which eventually leads to the engine suffering. At this point, ask yourself – what does a bad spark plug look like?

That’s where all your secrets lie. The tip of the spark plug can be damaged, causing a misfire, sputtering or rickety sounds. This will inevitably lead to increased exhaust, decreased power, and frequent visit to the gas station.

5. Idling

If you ever hear jittery noises or experience consistent jerks in your vehicle even while it’s idle – you have a problem. The trouble is nowhere but in the spark causing misfires in the engine. Sign of bad spark plugs also involves the engine to sound an incoherent pitch or just rougher than usual.

When and How to Replace the Spark Plugs:

Look out for these signs to know when you must replace the spark plug:

  • When the owner’s manual instructs to change it.
  • When you’ve roughly crossed 30,000 miles.
  • High performance will wear them down quicker.
  • If the material isn’t made of iridium or platinum, worn out will be faster.
  • When you notice oil leaks.
  • Higher revs will need a quicker change in spark plugs.
  • Now that we know all the dirty details, it’s inevitable to get your hands covered in grease and grime. But trust me, the results will be worth it all. We know what can bad spark plugs cause, and I dread it so much to the point that I’ve learned how to overcome it myself.

    You may be interested: Can bad spark plugs cause limp mode

    Follow these steps to replace your worn spark plugs.

    1. Locate the failing spark plugs in your vehicle.
    2. Clean up the area of work. You can use vacuum hoses or blast air around your focused area.
    3. Don’t be in a hurry to remove the plugs yet. Let your engine cool off before attempting it.
    4. You may now remove the ignition boot or coil. Disconnect the electrical connector and jerk it off the boot.
    5. Remove your current worn spark plugs by unscrewing them. Remember to remove or blow off any dirt that could be encircling the plug.
    6. You must measure the spark plugs gap where the measurement could be between .028-.060inches. For gaps that are too small, you can coerce it by prying the gauge upwards. For gaps that are too large, simply tap the electrode side on another hard surface.
    7. Check the condition of your current spark plugs. Few big ‘no’s are located when you see the following - slime, bent, rust, white cast, or a broken spark plug. A build-up of these categories means that there’s no going back, just throw them away without delay.
    8. Replace with the correct spark plug. And by ‘correct,’ it means to check the measurements, range, gap size, material, and everything in between that goes into getting yourself the perfect match. You can also replace it with the same manufacturer’s spark plug, which has lost its potential. This will save you the extra hassle. To install the perfect plug, you can also refer to the manual or the manufacturer’s website.
    9. Apply a thin layer of grease as a lube around the spark plug before you install it in the coil. The grease coating will prevent misfires and make the removing-installing process smoother.
    10. Place the vanity cover back, fire up the engine, and drive like it’s your first time!

    Spark Plug Replacement Cost:

    Let’s address the elephant in the room – the spark plug replacement cost. An average estimate for spark plugs is around $30. Your best option would be to DIY rather than a professional or mechanic because that would cost you another $100-$200.


    About the Author JamesL Davis

    James is a certified auto technician specializing in commercial vehicles. With 30 years of experience under his belt, James has encountered almost every type of automotive issue there is! Besides his day job at the repair shop, he is also an amateur race car driver.

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