How Often Should I Replace The Spark Plugs (3.8L Ford Mustang)

The humble spark plug is such an inexpensive component but when it fails (or its performance degrades), you're gonna' have a cylinder misfire on your hands (not to mention a cylinder misfire trouble code to light up the check engine light).

So if you've been wondering what spark plug you should use, or how often they should be replaced, or if it's something that you can do yourself then this is the tutorial you need for those answers.

What Does A Spark Plug Do?

Each of the six cylinders of your Ford Mustang's 3.8L V6 engine needs air, spark, and fuel to be able to produce power.

The spark plug is the component that provides the spark to ignite the air-fuel mixture swirling in the cylinder.

Symptoms Of Worn-Out Spark Plugs

Depending on how worn out the spark plug is, it will either cause a rough idle condition or a cylinder misfire condition. And if the spark plug is causing a misfire, you're gonna' have a corresponding misfire trouble code lighting up the check engine light on your Ford Mustang's instrument cluster.

You'll see one or more of the following misfire trouble codes:

  1. P0300: Random Cylinder Misfire.
  2. P0301: Cylinder #1 Misfire.
  3. P0302: Cylinder #2 Misfire.
  4. P0303: Cylinder #3 Misfire.
  5. P0304: Cylinder #4 Misfire.
  6. P0305: Cylinder #5 Misfire.
  7. P0306: Cylinder #6 Misfire.

Wear and tear is not the only thing that can cause a spark plug to fail or cause a cylinder misfire condition.

Another common problem, that will cause the spark plug to stop sparking, is carbon buildup blocking the air gap betwenn the center and side electrodes (caused by the engine burning oil inside the cylinder or cylinders).

Carbon build-up that causes the air gap of the spark plug to close is something usually seen in high-mileage engines.

One other symptom that you'll notice, when the spark plugs are worn out or have carbon buildup closing their air gap, is bad gas mileage and a lack of power under load.

What Causes A Spark Plug To Stop Working?

The spark plug is designed to deliver spark to the inside of the cylinder it's bolted into. It's this very spark that eventually will wear down the center and side electrodes. This doesn't happen overnight but it will happen.

As I mentioned before, wear and tear is not the only thing that will keep a spark plug from sparking.

Carbon build-up blocking the spark plug's air gap is another type of problem that will cause the spark plug to stop working.

Which Spark Plugs Should I Buy?

Your 3.8L V6 Ford Mustang came equipped with Motorcraft spark plugs when it rolled-out out of the factory.

These are the spark plugs that you should buy when it's time to replace them.

Having said that, you'll notice that there are many brands of spark plugs. And most of them if not all will work on your Ford Mustang.

Some of these spark plugs are expensive and cost more than the original Motorcraft spark plug. My suggestion to you is that if your Ford Mustang 3.8L engine is burning oil and the spark plugs you're pulling out have carbon buildup on them, then use the most inexpensive ones.

Here's the reason why: Even if you were to install the most expensive spark plugs, you're still gonna' have to replace them at a much shorter interval (just like you would the cheaper ones) because the engine is fouling them up with carbon.

Important Suggestions And Tips

Replacing the spark plugs on your 3.8L Ford Mustang can be challenging but not impossible and can even be fun.

The cool thing is that you don't need a bunch of expensive tools to replace them. And you can also find written and video tutorials on the Internet on how to do it.

If you do take the plunge and replace them yourself, here are a couple of suggestions:

TIP 1: Replace the spark plugs with a cold engine. If the engine has been running for any amount of time, it's important that you let the engine cool down completely before attempting to remove the spark plugs.

You can place a box fan (or any other type of house fan) on top of the engine to cool it down faster.

If you attempt to remove the spark plugs from a hot engine, you run the risk of stripping the threads of the spark plug holes in the cylinder heads (which are made of aluminum).

TIP 2: Check the air gap of the new spark plugs with a spark plug gapper.

If the packaging of your spark plugs indicates that they are already pre-gapped, I suggest that you check the air gap anyway. Over the years I have diagnosed and resolved many misfire problems that were caused by pre-gapped spark plugs that were not gapped correctly.

If you're using multi-electrode spark plugs, like the Bosch Platinum+4 spark plugs (which have four side electrodes), then you don't need to check the air gap.

TIP 3: Use a torque wrench to tighten the spark plugs where possible. Where possible you might be asking? I mentioned this because some of the spark plugs on the 3.8L V6 Ford Mustang engine are not very accessible and you might not be able to fit a torque wrench in a tight place to torque them (when you are tightening them).

If you over tighten the spark plugs, you could possibly strip the threads in the spark plug holes and have a major headache on your hands.

If you don't tighten them enough, they could work themselves out while you're driving down the road. And this too could possibly damage the threads in the spark plug holes.

More 3.8L Ford Mustang Tutorials

You can find more tutorials for your 3.8L V6 Ford Mustang in the following index:

  1. Ford 3.8L Index of Articles.

Here's a sample of the tutorials you'll find in the index:

  1. How To Test The TPS With A Multimeter (1994-1995 3.8L Mustang).
  2. How To Test The Radiator Fan Motor (1997-1999 3.8L Ford Mustang).
  3. How To Test The Fuel Injectors (1994-1995 3.8L Ford Mustang).
  4. Constant Control Relay Module (CCRM) Circuits (1994-1995 3.8L Ford Mustang).
  5. Constant Control Relay Module (CCRM) Circuits (1996-1997 3.8L Ford Mustang).
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