WELCOME TO OUR Changing a spark plug PROJECT
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Summary: In this guide you will learn how to identify your cars spark plug/high tension leads and replace them with a new set.
How to change a spark plug
Please note that this is only a general guide and is not specific to any one make or model of vehicle. For more detailed information on your own particular car, please consult a workshop manual specific to your own make and model!
Please read this first
If you have recently driven your vehicle, please leave it for at least an hour for the engine and other components to cool down. If you do not you may risk injury!
Required Tools:
1. Socket/Ratchet wrench.
2. 4” socket extension (longer maybe required).
3. Spark plug socket.
4. “Universal Joint” angle adapter (Maybe required for hard-to-reach areas).
5. A pair of needle-nose pliers (depending on the type of engine and ease of access to the plugs).
6. Feeler Gauge or spark plug gapping tool.
7. Small hammer.
8. Set of new spark plugs. (Make sure these are the correct plugs for your make and model of car. On most new cars the part number of the plugs should be noted in the engine bay. For some older cars you may need to do a little research).
9. 1 x flat head screw driver and 1 x philips screw driver
10. 10mm socket
11. Set of new spark plugs (check your vehicle user manual for exact part numbers)
Step 1 – Open the bonnet
Open the bonnet of your vehicle via the release catch normally located just under the dash board on either the driver or passenger’s side, walk to the front of the car and slide your hand under the bonnet and squeeze the latch. When the latch releases prop the bonnet up using the provided support.
Some vehicles feature a “sound suppression” cover which will cover the entire top of the engine. This will need to be removed to gain access to the spark plugs. This is usually secured in several positions.
Step 2 – Locate the plugs
Now that you have access to the engine you now have to locate the spark plugs. If you have a four cylinder engine, the spark plugs will be situated on top of the engine, in a row. If you have another engine type such as a V6, or a V8, the plugs will appear more to the side of the engine and run from front to back (in most cases!). (If you are working on either of these engine types, the job may be a little trickier as space is more limited and things will become harder to access). If you have a 6 cylinder engine, they may appear on top or to the side.
An easier method of locating spark plugs is to follow the HT leads to each plug. You may notice a number of thick rubber-like wires. These are the HT leads. One end of each lead is attached to the distributor cap and the other to each spark plug.
Depending on the age and type of car, the HT lead may feature a “rubber cap” that will obscure the view of the plug (this is to prevent moisture/water from affecting the plug)
Step 3 – Removing the HT lead
Now that you have located each plug, you may be thinking about pulling all the HT leads off of each plug, DON’T! Each spark plug fires in a specific order and if you mix the leads up with what plug they should go to then your car will miss-fire and not run correctly. The easiest and most stress free method is to do one plug at a time! This way you should not mix them up.
TIP: in the event that you did not read the above and have now pulled all the HT leads off, you may be able to re-trace which lead goes to which plug by its length. All HT leads are a different length depending on how far each plug is away from the distributor cap so, with this in mind the shortest lead should go to the first plug and so on!
Starting with the first plug on the left of the engine, pull the HT lead off of the top of the plug by grasping it as close to the top of the engine as possible. This may need a little persuasion as if they have not been moved for a while the natural heat of the engine may cause the lead to bond to the plug slightly. (If you have a four cylinder engine with twin over-head cams, the plug should be located at the bottom of a slight hole). In this case, the HT lead will feature rather a long rubber boot that covers the plug and the top of the hole that the plug is located in.
TIP: It is a good idea not to simply grab the lead and pull it off, as I said previously, grip the lead as close to the engine or as close to the base of the plug as you can. By just grabbing the lead and ripping it off you risk pulling the lead apart. Although it is a good idea to change the HT leads along with the plugs, they may be perfectly fine and you will end up having to waste money on a brand new set.
Step 4 – Removing a Spark Plug
Now that the first plug has been exposed and you can access it get your spark plug socket, wrench and socket extension (and universal joint adapter if you are working on for example a V8 engine where the plugs towards the rear of the engine bay are hard to reach) and put them all together. (If you are using an adjustable wrench, make sure it is set to undo which is anti-clockwise).
Slot the plug socket down onto the plug. You may need to spin it around slightly and apply a little pressure to make sure that the socket fits over plug securely and goes down onto it until (in most cases) it touches the cylinder head. Now undo the old plug by turning the wrench anti-clockwise until it is loose.
As I have previously mentioned, if you are working on an engine with twin overhead cams, the plug may be located in a hole. If there is enough room to get them in there, put your thumb and fore-finger into the hole and grip the top of the plug and pull it out. If not, get your pair of needle-nose pliers and grip the plug to pull it free.
TIP: with the old plug now removed from your engine, it is a good idea to inspect it as this can give you a good idea of the general health of your car. The plug should appear to be a little black and there should be soot present at the base (by the base, I mean the bottom of the plug, around the electrodes). If the plug is over oily or if it appears to be white then this can indicate more serious problems such as worn piston rings and engine overheating.
Step 5 – Fitting the new plug
Before you actually fit the new plug, it is always a good idea to compare your old plug with your new one. Do they look the same? Are your new plugs the right ones?
If you purchase plugs specifically for your vehicle, they should come already set with the correct gap. (When I say gap, I mean the gap at the bottom of the spark plug between the center electrode and the ground electrode).
If you have an older car or you have purchased a set of generic plugs then you may want to check and set the gap. Although this is not a hugely important thing to do and your vehicle should still run sufficiently without setting the correct gap, if you do set the gap to the manufacturers specifications it may increase the efficiency of the vehicle.
In order to find out what the correct gap space should be for your vehicle, you may need to do a little research.
When you have found this information get your feeler gauge or spark plug gapping tool and select the correct width leaf. First, run the leaf across the gap to see how much you have to adjust. When adjusted correctly the leaf of the feeler gauge/gapping tool should fit snugly in the gap and you should be able to move it.
Now, pick up your hammer and hold it with the hammer end facing upwards. Gently tap the bottom of the plug (the ground electrode) on the hammer twice, now check the gap. If it is snug then you are done, if not, tap the plug again, but only once and then check the gap.
You are now ready to fit the new plug.
With the plug between your thumb and fore finger, slot the plug down into the hole, being careful not to knock the plug around as this may damage the threads or adjust the gap.
It is a good idea to start screwing the plug in by hand as you have a lot more feeling and can gauge whether the plug is going in straight or whether you are running the risk of cross-threading it (This can be a very costly mistake).
If you are confident that the plug has gone in, in a straight line and that it has followed the threads correctly, keep screwing it in until it goes tight.
When you have got to the point that you cannot screw it in by hand any more, put the socket back on remembering to set it to do-up (clockwise).
Screw the plug down until it begins to go tight. When you have reached this point, give it another slight tweak just to pinch it down. (Remember, do not over do it as you will run the risk of stripping threads and in a worse case scenario this could mean a cylinder head replacement).
With the plug now screwed down into place, re-fit the HT lead to the top of it and you have now successfully replaced one spark plug.
For the rest of the plugs, repeat steps 3 – 5.
Step 6 - Testing
Now that you have completed the changing of all the plugs and re-fitted the HT leads, clear away all unnecessary objects such as tools from the engine bay and start the car up. Hopefully, if all is right, it should start first time and purr like a kitten. If not, the likely hood is that you have got one of the HT leads on the wrong plug and the engine in not firing in the correct order. To remedy this, you will have to research into your engines firing order correspond the firing order to the points on the distributor cap and set the engine to top dead center and then reposition the leads in the correct order. So, as you can see from this it is a lot easier just to do one plug at a time!
You have now successfully completed this project.
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