What Do The Spark Plugs Do? (1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997 Ford Bronco, F150, F250, F350)

The spark plug is a small component of your Ford F-Series pickup's ignition system, yet it performs a super critical function in keeping the engine running.

In this article I'll answer some of the most commonly asked questions about the spark plugs.

APPLIES TO: This tutorial applies to the following vehicles:

  1. Ford Bronco: 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996.
  2. Ford F150: 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996.
  3. Ford F250: 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997.
  4. Ford F350: 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997.

What Does A Spark Plug Do?

The sole purpose of the spark plug is to ignite the air-fuel mixture within the cylinder that it's connected to.

And it does this by transmitting a spark from its center electrode to its side electrode.

This is the spark produced by the ignition coil and that is supplied to the spark plug via the distributor and the spark plug wires.

Symptoms Of A Bad Spark Plug

If a spark plug isn't sparking, then it's cylinder is going to misfire.

Besides a misfire problem, you're going to see one or more of the following symptoms when a spark plug fails:

  • Rough idle.
  • Bad gas mileage.
  • Extended engine cranking (engine takes longer than usual to start).
  • A heavier than normal exhaust smell coming out of the tailpipe.
  • The engine is not as peppy as it used to be.
  • Hesitation when you accelerate the vehicle on the road.
  • On OBD II vehicles, you'll see one or more of the following trouble codes:
    • P0300: Random Cylinder Misfire.
    • P0301: Cylinder #1 Misfire.
    • P0302: Cylinder #2 Misfire.
    • P0303: Cylinder #3 Misfire.
    • P0304: Cylinder #4 Misfire.
    • P0305: Cylinder #5 Misfire.
    • P0306: Cylinder #6 Misfire.
    • P0307: Cylinder #7 Misfire.
    • P0308: Cylinder #8 Misfire.

What Causes A Spark Plug To Stop Working?

Quite a few different things can cause a spark plug to stop sparking.

Here are the most common:

  • Normal wear and tear. In other words, they simply wear out.
  • Carbon deposits blocking the air gap between the center and side electrode.
  • Spark plug is damaged during installation.

When the spark plug's air gap is blocked with carbon deposits, spark will not jump between the electrodes.

Carbon deposits blocking the air gap between the electrodes usually only happens on high-mileage engines that are burning oil within the cylinders.

You can tell these engines apart because:

  • They burn oil and have blue smoke coming out of their tailpipe.
  • These engine require being topped off with engine oil on a regular basis.

How Do I Know My Spark Plugs Need Changing?

Nothing is written in stone that says when it's time to replace the spark plugs since quite a factors can contribute to their failure.

Usually, the spark plugs are replaced when one of the following conditions is met:

  • You've removed the spark plugs and they are showing signs of heavy wear and tear.
  • The spark plugs are causing an engine performance problem.
  • You're following the recommended spark plug change interval layed down in a repair manual or owners manual.

Which Spark Plugs Should I Buy?

The Ford Motorcraft brand of spark plugs are the original equipment spark plugs that your F-Series pickup came equipped with.

These are the spark plugs that I recommend you buy when it's time to replace them on your F150 (F250, F350) pickup.

In my opinion, getting the best performance out of the spark plugs means buying the Motorcraft brand of spark plugs.

Now, having said that, any spark plug that's specifically designed for your F-Series pickup (year, engine size) will work.

Should I Use 100,000 Mile Spark Plugs?

Spark plugs that are advertised as having a service life up to 100,000 miles have platinum or iridium tipped electrodes. Regular copper spark plugs, won't last as long.

Now the catch here is that if the engine is in perfect working condition (e.g. it's not burning oil) then you'll definitely see these spark plugs give a service life of about 100,000 miles.

But if the engine in your Ford F150 (F250, F350) is burning oil, you're not going to see anywhere near 100,000 miles on those spark plugs. Carbon buildup will eventually close the air gap between the spark plug electrodes and cause a misfire.

Important Tips And Suggestions

When replacing the spark plugs in your Ford F-Series pickup, keep in mind the following tips and suggestions:

TIP 1: Let the engine cool down completely before removing the spark plugs. If you don't let the engine coool down, you run the risk of damaging the spark plug threads of the spark plug holes in the cylinder head.

Stripping the threads of the spark plug holes is a nightmare that you don't want to experience.

TIP 2: Use a spark plug gapper to check the air gap of the new spark plugs before installing them. I strongly recommend that you double check that the spark plug gap is correctly set to your vehicle's recommended specification when installing spark plugs.

Don't trust that they are gapped! I've solved many driveability problems that were due to incorrectly gapped spark plugs.

TIP 3: Label the spark plug wires with the cylinder number they belong to BEFORE replacing the spark plugs. This will keep your from losing the spark plug wires' firing order.

TIP 4: Use a torque wrench to tighten the spark plugs. If you don't tighten the spark plugs enough you run the risk of having them come out as you're driving down the road. This could also damage the spark plug hole threads in the cylinder heads.

If you over tighten the spark plugs, then you run the risk of damaging the threads of the spark plug hole.

The way to avoid any of these problems is to use a torque wrench to tighten the spark plugs. Now, it's easier said than done because some of the spark plugs are in very tight places (some just can't be tighten with a torque wrench). Still, you won't go wrong if you use a torque wrench on the ones you can.

More Ford F150, F250, F350 Tutorials

You can find more tutorials Ford F150, F250, and F350 in the following index:

  1. Ford 4.9L, 5.0L, 5.8L Index Of Articles.

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

  1. How To Test The Ford Ignition Control Module (Distributor Mounted).
  2. How To Test The Ford Ignition Control Module.
  3. Throttle Position Sensor (TPS) Test (Ford 5.0L, 5.8L).
  4. How To Test The Ford Mass Air Flow (MAF) Sensor.
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Ford Vehicles:

  • Bronco 4.9L, 5.0L, 5.8L
    • 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996
  • F150 4.9L, 5.0L, 5.8L
    • 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996
  • F250 4.9L, 5.0L, 5.8L
    • 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996
  • F350 4.9L, 5.8L
    • 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997