Changing your Spark Plugs

Spark Plugs they really are that simple to change over

Don’t waste money, try out this simple fix!


Spark plugs play a major role in your cars performance and ability to run correctly. Spark plugs ignite the fuel inside your engine chambers which power your car, without them you wouldn’t get any combustion causing the engine to fail(No one want’s that!).

In today’s market you can get Spark Plugs for just a few £’s so, to be quite honest if you think they need doing then just grab some and change them. Changing your spark plugs is actually a lot easier than what mechanics lead you on to believe.


Do My Spark Plugs Really Need Changing


There are some signs to look out for which may resemble that your car is due for a spark plug change. Here are some signs to look out for:

Engine has a rough idle (juddering, random revs).

In a large amount of cases a rough idle is down to the ignition system of your car. This could be any one of the following: the ignition leads, spark plugs, ignition coil or something else. It’s best to check the spark plugs first as they are the cheapest and easiest to test and replace.

Problems Starting your Car

Don’t be quick to replace that starter motor! It could be something simple as worn out spark plugs. Always double check parts before going out and buying something that may not be needed.

Your engine misfires

When your engine misfires it will causes the vehicle to halt for a fraction of a second, then it continues it’s usual movement. What this means is the vehicle isn’t functioning as smoothly as it should be. This is normally because one or more cylinders are not firing properly. This can also lead to higher amounts of emissions, which you may or may not notice(I am sure the person behind you might though).

Your spark plugs are used to ignite the fuel in the engine cylinders so it would be wise to check the coil, leads and spark plugs for this one to see what’s at fault.

Engine Surging

When your driving the vehicle will act as if it’s jerking or randomly starting and stopping. It is not at all safe and can be quite a problem whilst in traffic especially if it has problems with starting and stopping. Best to get this one checked out ASAP!

Higher Fuel Consumption (Lower MPG)

If you have noticed you are no longer getting much mileage out of your car then chances are it could be down to your ignition system not performing correctly. The problem is if your spark plugs have deteriorated then your looking at around 30% fuel loss due to incomplete combustion. Change your spark plugs and this should improve you fuel consumption.

Poor Acceleration

Putting your foot down on the pedal and noticing a lack of power? If there are any changes in your accelerators performance it’s best to have a look at the ignition system (spark plugs, ignition leads and ignition coil) 9/10 it will be down to the ignition systems performance. Unless you have a slipping clutch, but that’s another matter all together. Best to check the spark plugs first.

If you have noticed any of the above problems then it is about time you changed them spark plugs.


Before you Begin


So your now 100% sure you want to change your spark plugs and your now ready to jump right in. Before we begin it would be wise to purchase some spark plugs first. You may think it’s a bit odd to purchase spark plugs if your not sure they are at fault. Whilst that is true, spark plugs are very cheap and affordable. So it’s nice to have a spare set just in case you need to do this repair later down the line. Spark plugs ware out it’s a well known fact, so you will need to replace them, if not now then later.

When purchasing spark plugs you must make sure they are the correct spark plugs for the car. Failure to get this right can end up with all kinds of problems with your car. You could go to your local Halfords but they are quite expensive from there, and there stock isn’t exactly extensive. I normally get my spark plugs from Euro Car Parts because they are cheap as chips. Check your owners manual for the correct spark plugs for your car.


Tools You Will Need For The job


In the good old days you had to purchase what was known as a feeler blade to set the gap on your spark plugs, this was more time consuming than anything and you would have to buy a specialist tool to “bend” the plugs into shape. Now a days in most cases all spark plugs are all ready set up for the correct gap for the vehicle so it’s just a matter of swapping the plugs over. But if your unlucky see this guide on setting the gap on your spark plugs.

Now for the tools you will need:

Socket Set, Wrench, Screwdriver.

For any screws, bolts and parts to be removed to gain access to the spark plugs. Your spark plugs are on the engine head. Chances are there is a unit covering your spark plugs that will need to be removed to replace your spark plugs.

Torque Wrench


A simple torque wrench

Torque Wrench


A torque wrench is designed to allow the user to tighten up parts of a car to the correct “Torque” the wrench will click when the correct torque has been met. This makes sure that the part your tightening isn’t too tight or too loose. When it comes to changing spark plugs its vital you set the correct torque. To little and the spark plug will not perform correctly too much and it will have a shortened life or you may damage the thread of the engine (you really don’t want to do that). So it’s best to get hold of one of these to make sure it’s done correctly.

This tool is vital for a lot of key jobs when fixing your car they can be quite pricey for top spec ones. But for this job a simple Torque wrench for under £40 would do the trick. Visit your local car repair shop and ask them what torque wrenches they have on offer. If your serious about car repairs you must purchase one of these or youll have major problems later on.

Specialist Spark Plug Removal tool Or spark plug socket


How to remove spark plugs

The tool I use to remove spark plugs


You have 2 choices when it comes to removing spark plugs. Due to there place inside the engine head they are inside a long deep tube. You wont be able to use a normal socket to remove these plugs. You need to purchase either a specialist tool designed to reach the deep seated Spark plugs or a special socket set adapter. I don’t recommend those cheep flimsy socket set removers, because if the spark plugs are in quite tight then chances are you wont be able to remove them easily.

Halfords do a great range of specialist tools here I purchased the Laser one from here it’s a solid piece of kit and is magnetic too so makes the job so easy. Just make sure it’s the right size for your car, not all spark plugs are the same size.

Set of Spark Plugs
A pair of spark plugs

Spark Plugs


Spark plugs can vary from car to car, from their “gap”, size and the amount of spark plugs you need. So it’s best to check your owners manual to see how many your car requires. Failure to get the correct amount or the correct spark plug will give you nothing but grief, so double check to make sure you have the correct type and quantity there is no point in purchasing 4 spark plugs if your car needs 8!


As with any job requiring the use of changing any electrical parts of a car it’s always best to carry one of these around. We will show you how to test your ignition leads with a multimeter. It’s common practice to make sure there leads are in working order as if they are not it will also effect the car performance.

Now that you have all the tools you will need it’s time to begin!

Air Compressor, can of air or even a hoover

Before removing spark plugs you need to make sure the spark plug chamber is clear of any debris, some people use air compressors but to be honest a can of air or even a hoover with a small bit will do the trick. You don’t want any dirt falling into the engine head so make sure you clean out the chamber properly before removing the spark plug.


Locating Your Spark Plugs


**Before doing anything make sure your car has cooled down as the area your working on may be hot to touch. Go make yourself a brew and relax for 15 mins, should do the trick.**

The quickest most efficient way to locate your spark plugs is by checking your owners manual. If you don’t have one to hand it might make it a bit more difficult to locate. Follow this guide on how to find your spark plugs.


Locate your spark plugs

Image Taken From


Firstly your going to want to start with opening the bonnet(hood) of your car. Once opened look at your engine. Your wanting to look for some electrical wires that are quite thick 4 – 8 of them depending on what car your using. They will all look like the same wire just heading to different direction on the engine but coming from a gathering point on the engine. Spark plugs are located at the end of these wires.

Depending on which car you own your going to want to look for the following:

4 cylinder Engines

The Spark plugs are located either on the top or the side of the engine in a row pretty simple to change and locate.

In line 6 cylinder engine

The Spark Plugs will be on the top or the side of the engine head just follow the wires.

V6 and V8 Engines

Spark plugs should be evenly spread on either side of the engine. You should see the wires “mirror” each other.

On most modern cars they will have an engine cover. In some cases these can be a pain to remove as most companies like to use security screws and other awkward positioned bolts. Just feel around the cover and remove all nuts, bolts and screws attached to the cover, before remove it. Be careful as to not break the engine cover. If in doubt always double check your owners manual as to not break any parts when removing your engine cover.

You should check your owner’s manual and look up where your spark plugs are, how many you have, the correct “gap” (if your plugs need to be set) and the size socket needed to remove them as sizes do vary. It is common practice to also number the corresponding leads to the cylinder so you don’t put the ignition leads on the wrong order. Whilst performing a spark plug change it is good practice to inspect the leads for any damage or cracks as replacement leads may be required. We will show you how to test these leads with a multimeter later in this guide.

Removal of Your Old Spark Plugs

Ignition Leads

Once you have located your spark plugs you will first need to remove the ignition leads. These are long leads that hold onto the spark plug to provide power to the spark plug. Do not pull on the wires as you may damage the cable inside of the lead. Just use the tops of the leads they are shaped like a handle. Some are a bit stiff but a bit of pulling will allow them to come out. If they are very hard to remove, chances are it’s time for a renewal.

Your going to work in a set order as to not get the leads and spark plug sockets mixed up. Choose where your going to start and where your going to end and if possible label the leads and socket holes. i.e 1, 2, 3, 4…. Once you have done this it’s safe to remove the first lead.

Remove the first ignition lead from the coil pack and spark plug socket. Now check the ignition lead from one end to the other. Your wanting to look for any cracks bends or tears to the cable. You will also want to check inside of the lead it’s self. Where the lead meets the coil pack you should see a metal tip. This tip should have a copper band around it, if this has snapped off replace the lead. This can happen when removing the ignition leads due to wear and age of the lead.

If there are any slight problems with the lead it’s best to replace it now instead of waiting till it fails.

Testing your ignition leads

If your sure the leads fine it’s still common practice to test the ignition leads resistance to ensure it’s working correctly. The best way to do this is using a multimeter. Follow these steps to test your ignition leads:

Set your multimeter to 20 kΩ

Attach one contact to each end of the cable

Read the resistance

Permissible resistance values are taken from the NGK website

  • Ignition cable with a copper core: 1 to 6.5 kΩ
  • Inductive resistor and carbon resistor: The value is calculated based on the resistance per meter multiplied by the length of the cable, plus tolerance
  • Ignition cables with inductive resistor: Here the resistance can be between 2.2 kΩ and 8 kΩ
  • Ignition cables with carbon resistor: The resistance per 1 m cable is 10 kΩ to 23 kΩ

If everything looks ok and the resistance is correct then it’s safe to keep the ignition leads. Most mechanics would change the leads without a 2nd thought. So it really is best to check the ignition leads to save yourself some extra cash. Leads can vary in price from vehicle to vehicle.

Removing your first spark plug

Before attempting to remove your first spark plug ensure that the spark plug chamber is clear of any debris. Once your sure there is no debris in the chamber it’s safe to start removing your spark plug.

Grab your spark plug removal tool and begin to turn the spark plug counter clockwise. It may be stiff at first especially if they are old spark plugs. You should hear that relieving crack noise when you break the seal of the plug. The hardest part is getting the plug out of it’s chamber. If you have a magnetic spark plug removal tool it will just pull out, but if you don’t the best way to remove a spark plug is to use the ignition lead. Once your sure your spark plug has reached the top of the thread and is now loose just push the ignition lead back onto the spark plug and pull it out. It should suck onto the spark plug making it easier to remove.

Checking your spark plugs

Now that you have removed your spark plug it’s time to check them over. Some people just test the gap and if it’s off well it’s pretty much time to swap the spark plugs over. I normally just go by the overall appearance of the spark plugs. Just compare your new spark plug with your old one and you can see if there is any differences.


Replace your spark plugs

Old Vs New Spark Plugs


You should be looking for corrosion or any wearing of the spark plug also the colour of the spark plug can tell you some key information about your cars engine. Your wanting your spark plugs nose tip to be the colour of light brown to tan, this shows that your engine is in good condition. Once finished with overall checking of the spark plugs you can now be discarded the spark plug as it cannot be reused.

Inserting your first spark plug

Now its time for you to insert your first spark plug into your engine. Now be careful as to not bang the ends of the spark plug as damage may occur and cause the spark plug to either not work or not be as efficient. The best method to installing a spark plug is to use a bit of old hose that will fit on the spark plug as it has less chance of the threads being ruined by wrongly turning the spark plugs, the hose should bend when turning the spark plugs incorrectly. You can also use your ignition lead to help hold the spark plug as you turn the first few threads. If you can manage to turn it by hand then do it very carefully and make sure it’s done correctly.

Once your sure the spark plug is safely on the first few threads you will want to get your spark plug removal tool or socket and start to tighten the spark plug don’t tighten it too hard. You will then want to get hold of your torque wrench and set the wrench up to the correct torque that’s listed in your owners manual. All car owners manuals will have the torque specifications for tighten spark plugs, if you don’t own a owners manual you can either buy one from here or check out popular forums for your cars make and model. When you hear the clicking your done.

** You must tighten your spark plug to the correct torque or else it may cause shortened life of the plug or worse harm the engine, never under or over tighten spark plugs**

Now that the spark plug installation is complete your going to want to get your ignition lead (if faulty replace with a new one) and place it back onto the spark plug and ignition coil pack. Then it’s time to move onto the next spark plug. You will want to repeat this process until all spark plugs have been installed correctly. Just remember this is not a rush job take your time and ensure that no debris falls into the engine head or you round off any of the threads, these are both no good for your car.

Once complete re assemble all parts including the engine cover if your car has one. Ensure that all bolts, fixtures, nuts and screws are placed back in the correct places. Last thing you want to do is start up your car and find out you forgot to hook up the air manifold.

It’s now time to test the car out. If everything was done correctly your car should start up fine and you should notice you get a bit more MPG. You may even notice that some of your cars problems have now been fixed. If you still notice any more of the problems listed at the start of this guide you should check your coil pack, the box your ignition cables are attached to, this may be the culprit of your problems. There easy to replace but can be a bit pricey as they normally come as a complete set. Sometimes its best to grab one off eBay.

If you think this may be the case check out our guide on “How to change your ignition coil pack” it may solve your car engine problems.

We hope you enjoyed installing your new spark plugs and now feel great that you have saved yourself a decent amount of cash on such a simple repair.


Regards, The Beat The Mechanic Team.