Ford Mustang GT: How to Replace Spark Plugs

Introduction

The spark plugs in the Ford Mustang GT are located on the cylinder head on top of your engine. They work together with the fuel and air mixture to spark up your car, creating a small explosion that allows your car to start. When the spark plugs burn, they lose the ability to spark properly, which results in loss of power, slow start, and often times your car won't start at all. Replacing the spark plugs is one of the few procedures left for car owners to replace, because it is rather simple and straightforward. Be sure to purchase the proper spark plugs for your year and model. Read below to learn how to change the spark plugs yourself in the Mustang GT.

Time, Cost, Difficulty

This job requires basic tools and no special skills.

Materials Needed

Materials Needed

• Adjustable crescent wrench
• 12mm socket
• 5/8 spark plug socket with extension
• Torque wrench
• PB Blaster
• Anti-seize lube
• Dialectic grease
• New spark plugs

Step 1 - Disconnect Battery

Remove the negative (black) battery terminal, then wrap it in a towel to prevent it from touching any metal and creating a spark.

Step 2 - Remove strut tower brace and covers

If your GT is equipped with a strut tower brace, you will need to remove that before continuing. You will also need to remove your engine cover and the two valve covers. Depending on the year of your Mustang, you will likely have to remove a couple of hoses to get the valve covers off.

Step 3 – Remove coil pack wiring harness and bolt

Each coil has an electrical coil pack wiring harness connected to the top of it. To remove these electrical units, you will have to squeeze the tab and pull them out. Extract the coil packs by unbolting the 7 or 8mm bolt to the right of each coil pack. In the GT, there will be eight total. 

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Step 4 - Remove Coil Pack

Pull the coil packs out gently. There will be eight of these as well. 

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Step 5 - PB Blaster

Before extracting the old spark plugs, spray them with PB Blaster and wait 15 minutes. This allows the spark plugs to loosen up so they don't break when you're removing them.

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Step 6 – Remove spark plugs

Use a 5/8" spark plug socket and long extension rod to remove the old spark plugs. If they are torqued too tightly, don't force them. Try some more PB Blaster or check the forum for other loosening agents (such as WD-40). Once they are loose, you should then be able to twist the old spark plugs out.

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Step 7 - Examine old spark plugs

This old spark plug doesn't look too bad, just a little worn. But they can look much worse, as shown in the inset. In any case, a new spark plug will create a better connection and a more reliable start.

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Step 8 – Anti-seize lubricant

Smear a little bit of high-temperature nickel anti-seize lubricant on the threads before installing the new spark plugs. This will prevent them from getting stuck the next time you want to remove and replace them. You don't need too much and you want to spread it around the threads evenly.

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Step 9 - Installing the new spark plugs

The same way they went out is the way you put them back in. Torque them to spec, which 126 in-lb or 10 ft-lb. Once they are tight, go a little tighter, but don't strip the threads. Then put the coil packs in the car. Be sure to add some dialectic grease* to them first for a good seal and contact (to avoid misfires). Place the boots back over the spark plugs and give them a wiggle to spread the dialectic grease around. Once everything is installed, and you've put your covers and brace back on and reconnected the battery, crank your engine, listen to that rumble, and enjoy the road that lies ahead!

*According to forum member Sharky, brake caliper grease is better than dielectric grease because it's not as good a conductor of heat and does just about the same thing as the dielectric. Motorcraft recommends the following chemicals and lubricants for spark plugs: 

Our thanks to Pureza Garage 704 for providing some of the images.

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