Spark Plug Install On 03-04 Cobra Mustang

Posted by on December 20, 2009 - more

Many people are fearful of changing their plugs, especially on the 2003 and 2004 Mustang Cobras. The reason for this is the spark plugs are deep down in the heads and they only have 4 threads per spark plug hole. This can lead to stripped threads or stuck sockets. Overall its generally very straight forward, especially if you have the factory set of plugs in the vehicle. You need minimal tools to perform this and its actually quite simple so relax, take your time and read through the how to before you start and you should have no major issues. I rate the difficulty of this a 1 our of 10. This install will also work for other 4 valve 4.6L engines, its basically the same type of things for those as it is for this. Also note the blue stripe painted on your head does not mean the heads are the revised 9 thread heads. Unless your car developed the head tick issue you pretty much have a 99% chance of having the regular 4 thread heads with the non revised coolant passages. They changed the plugs in the 03/04 Cobras so there is no one single plug that is OEM that works. If you have doubt take one out and look at it.

Spark Plug Install Sections
1. Parts you need to complete this job
2. What to do before you start working on the car3. Removal of the air intake and coil covers
4. Removal and install of the spark plugs
5. Double check yourself and finishing up
6. Spark Plug Part Numbers

Parts you need to complete this job

You really do not need many tools. Below is a list of what I used. You will notice antiseize , you may not wish to use this as some suggest against it. I choose to use it since the aluminum heads can be a pain and spark plug removal down the road can be harder with out the use of it.

Tools Needed:
1. 10 inch and 6 inch extension
2. Ratchet
3. 10 mm socket
4. Spark Plug Socket (5/8th with rubber fitting to hold the plug)
5. Inch/Pound Wrench (optional but strongly suggested)
6. Can of compressed air or an air compressor to blow out the spark plug tubes
7. antiseize (optional)
8. Connection Protector Dielectric Grease
9. Spark Plugs
10. Spark Plug Gap Tool
11. Painters tape and a pen to label the plugs as they are removed
12. Some towels or fender protectors to keep the car from becoming scratched

*NOTE: If you have modifications there may be a different spark plug you wish to use. In my case I will have a 2.93 Supercharger pulley and they suggest a TR6IX Iridium (or TR6 Copper) plug since its one range colder than stock. The stock plugs are Iridium. Mine cost 65 dollars for an example of what you should expect to pay for Iridium plugs. Expect about two dollars each for copper plugs. Copper require more frequent changes, but this can be a good thing as if you are running more boost than stock its great to keep an eye on your spark plugs. Never trust the gap, always check them. Stock plug gap is .52-.56. Iridium do not require as tight of a gap as copper.

What to do before you start working on the car

Before you start working on the car make sure your spark plugs are gaped correctly using a gap tool. Be gentle as Iridium is known to be easy to break the electrode off of. Once you are satisfied that the plugs are gaped correctly lay your fender protector or towels over the area you will be working to protect the cars paint. There is no need to risk a scratch.

Removal of the air intake and coil covers

Since there are so many intakes refer to your specific type on how to remove it from the vehicle. If it is an OEM intake then remove the MAF electric connector and unscrew the throttle body connection and then remove the air filter housing and slide the unit out. You will have one or two other things pluged into the air intake so please remove them as well before you pull your intake off of the vehicle. Take your time here and it will come out pretty easily. Now is a good time to clean or replace an air filter.

You will notice two 10 inch bolts on each coil cover. Unbolt these and wiggle your coil covers. If they do not pop right off then take a towel and a flat head screw driver and use the towel to protect the cam cover. Slide the edge of the flat head under the cam cover and pry up, it should pop right off. If your rubber coil cover gasket is messed up replace it as they keep debris out of your coil and spark plug tunnels. After removed gently slide them out and off of the car and place them somewhere safe so you wont scratch them up.

Removal and install of the spark plugs

The passenger side is the harder of the two so I started here. You will notice the coils (black things) gently pull up on them and they will pop right off. Slide them up and out.

Now with the coil out of the way you can see all the way down to the plug.

Use a bright light to make sure you remove all debris. Blow out the hole with your compressed air really good before you remove the spark plug. Any debris left can work its way down and into the cylinder which is bad.

Take the 10 inch extension and the spark plug socket and slide it carefully into the spark plug tunnel. You might have to wiggle it a bit to get it started in the hole but be careful as once you are past the first little bit it should slide right down. Make sure you don’t force it to much and end up smacking it into the spark plug (especially bad if you are installing the plug not removing)

Use the ratchet and slowly turn to remove the plugs, its a great idea to ensure you are turning to the left before you start this process. This is a simple mistake that can strip the threads so just be safe and make sure yo uare indeed turning the ratchet correctly to remove the plug. If they are the OEM plugs they may be a bit tight to remove. If you turn a bit you will feel it move all the sudden. Let off as soon as you feel this and then slowly turn the plugs. They will slowly come out and then you can slowly pull the extension out with the plug. I loosen a few turns and then take the ratchet off and remove the rest by hand generally to ensure no cross threading.

Take your tape and wrap it around the plug so that you can write where that plug came out of. I wrote “Pass Front 1” through “Pass Front 4” so I knew which plug went where. Choose any system you wish, but keep up with what plug goes where.

Now that the plug is our inspect the spark plug tunnel for any metal shavings (signs of cross threading). All should be clear. If so then we are ready to install the new plug. First we need to make sure the gap is correct, if you didn’t in the steps above do it now. If you choose to put antiseize on the plug threads now is the time. I put a small tab on my finger and gently turn the plug and apply it all around it evenly. I then take my finger and thumb and rub the threads to remove all I can. You want a very little antiseize , do not put to much. Less is more when it comes to this step. I tried to take a picture of how much I used, but the camera would not focus that close. Try to get antiseize on the entire thread area, not just the back or the middle. You can look at your old plugs to see the area of the plug that was in the threads while in the head if you wish.

Place the plug in the spark plug socket and gently ease it back into the head and down the tunnel. You must start the plug by hand. Slowly turn the extension making sure its as centered in the tunnel as you can get it to start the plug. If you at any time feel more than a tiny bit of resistance back off and start again. Take your time here. They should go in without a fight. Once you snug them as much as you can by hand then take the inch/pound wrench and set it to 15 newton meters (about 11 foot/pounds or 136 inch/pounds). You can not use a torque wrench its not accurate enough at such a low foot/pound amount. Tighten until you feel the plug stop, its quite noticeable. Then tq the plug until the wrench clicks (or beeps or what ever to signal the correct level has been reached). Click it twice and then remove it.

Now you need to place a little of the dielectric grease onto the coil before you slide it back onto the spark plug. Rub it around with a finger (that does not have antiseize on it).

Slide the coil back down the spark plug tunnel and you will feel it click onto the spark plug. Repeat this process for the other plugs. When you get to the plug under the throttle body it can be tricky. You may need two extensions and a wobble connector. You can also unbolt the throttle body (four 8 mm bolts at each corner, it is not a compression gasket so you will be fine if it does not rip on removal to reuse it) and lift up on it gently and it will pop right off. This will grand you the much needed access, I had to do this as I did not have any other small extensions to use. Inspect the gasket and if it was messed up you will have to replace it before reinstall. For the very back spark plug you will probably have to use your 10 inch and 6 inch extension together to get access. Wait on putting the throttle body back on until all coil’s have be reinstalled as it helps in working with those as well. Finish off with reinstalling the coil covers and the air intake. Make sure you plug in all of the connectors for the air intake.

Double check yourself and finishing up

It is always good to reflect and make sure you remembered everything. Make sure you used antiseize , dielectric grease, tq’ed each plug correctly, reinstalled each coil correctly, and anything else. Clean up around the areas you now have access to that you generally do not such as under the air intake. When you are happy and everything is reinstalled and ready to go (such as your intake that you had to remove) test starting up the car make sure it runs and idles fine with no misses. Use your factory plugs as a guide to check and see how the car is running. You can tell a great deal about how your car was running by inspecting your old plugs.

Spark Plug Part Numbers

NKG TR6 (copper) #4177
NKG TR7IX (iridium) #3690


  1. Wacko Biker says:

    That’s a great write-up.

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