You may find it shocking to hear, but ignition coils don’t last forever. For the most part, ignition coils are extremely simple components, but they can break down as time passes. If your vehicle’s engine is running rough or you aren’t getting the same power or gas mileage as in the past, it is possibly time for a replacement ignition coil. Here’s what you need to know about the different types of ignition coils and how to replace them.
Types of Ignition Coils
Before you pick up a wrench, you need to figure out what kind of automotive coil is in your vehicle’s ignition. Here are examples of each major type of ignition coil:
There are other coil types and shapes in use, but these are the most common ones you will find on the shelf of your local NAPA Auto Parts store.
How to Change a Single Can/Block Coil
Commonly found on classic cars, a single standalone canister or block coil sit on the engine itself or nearby on the vehicle chassis. It will have a single coil wire leading to the ignition distributor cap. Changing a standalone coil is about as simple as an automotive job gets.
- Turn off the engine.
- Locate the ignition coil.
- Remove the center coil wire from the top of the ignition coil.
- Remove the power wires connected to the coil. Typically, there is a positive and a negative wire connection. Make sure to note the wire connections. For example, you can mark the positive wire with red tape and the negative wire with black tape.
- Loosen the coil mounting bracket clamp.
- Slide the old coil out of the mounting bracket.
- Insert the new ignition coil.
- Reconnect the positive and negative wires.
- Reconnect the center coil wire.
- Start the engine to verify the repair. If the engine does not start, check all the electrical connections.
How to Change an HEI Coil
GM vehicles from the late-1970s to the 1980s used a single coil mounted directly to the top of the distributor cap. This made packaging a little tidier plus created for a very simple ignition solution.
- Turn off the engine.
- Locate the distributor.
- Remove the ignition coil cover by loosening the mounting screws. The ignition coil and wiring are now exposed.
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Note the location of the positive and negative ignition coil power leads inside the distributor cap. We recommend taking a picture with a cell phone or marking each wire with a piece of tape.
You may also have a ground wire connected to one of the corner mounting bolts. Note its location as well and how it is attached. Some coils use a solid metal ground bracket, which sits under the coil and can only connect one way. - Unplug the ignition coil power leads gently by lifting them straight up. You may need to use needle nose pliers if they have remained in place a long time. Make sure to only pull on the power lead spade connectors, not the wires themselves.
- Remove the coil retaining bolts.
- Lift the coil straight up for removal. Note that the coil has a contactor on the bottom allowing it to contact the spring connected to the rotor button below.
- Place the new coil inside the distributor cap, making sure the coil is seated with the wires facing the right direction.
- Slide the ignition coil power leads straight down into the distributor cap, making sure they are in the same location as you marked previously. Connect the ground wire, if so equipped.
- Reinstall the coil retaining bolts.
- Reinstall the ignition coil cover.
- Start the engine to verify the repair. If the engine does not start, check all the electrical connections.
How to Change a Coil Pack
Some vehicles, like 1990s GM and Ford vehicles, have coil packs located away from the spark plugs. However, spark plug wires are still used to pass electricity to each spark plug. A coil pack can have multiple output connections. Changing ignition coil packs isn’t too bad of a job if they are in an accessible area.
- Turn off the engine.
- Locate the faulty coil pack.
- Mark the spark plug wires. You can use painter’s tape and a marker or a silver paint pen to write directly on the spark plug wire boots. Or choose your own method. The important part is that you MUST connect the spark plug wires to the new coil pack in the exact location.
- Disconnect any other wires or connectors from the coil pack.
- Remove the coil pack mounting hardware (screws, bolts, etc.).
- Remove the old coil pack from its mounting surface.
- Install the new coil pack on the mounting surface.
- Reinstall mounting hardware (screws, bolts, etc.).
- Reinstall all wires, including spark plug wires.
- Start the engine to verify the repair. If the engine does not start, check all the electrical connections.
How to Change a Coil-On-Plug
Modern vehicles most commonly use a coil-on-plug arrangement where each individual engine cylinder has its own ignition coil connected directly to the spark plug. Technically, there is still a spark plug wire, it is just very short and you can replace it separately from the coil pack.
- Turn off the engine.
- Locate the faulty coil pack or packs. Keep in mind that some coil packs are possibly buried underneath the intake manifold or other engine components, making access difficult. If your engine is particularly difficult to access, you may consider replacing several coils at once. Repairs like this are labor heavy, so you might as well take care of any other potential issues like leaking valve covers or changing spark plugs now.
- Unplug the coil pack connector, taking care to not damage it as engine bay heat can make plastic brittle.
- Inspect the coil pack connector, taking care to remove any corrosion you find.
- Remove the coil pack mounting hardware (screws, bolts, etc.).
- With the coil pack now unplugged and loose, gently twist it back and forth to loosen any corrosion at the spark plug boot. If the coil pack will not turn, do not force it and move on to the next step.
- Gently lift the old coil pack straight up and away from the spark plug.
- Apply a light amount of dielectric grease to the end of the spark plug boot to help make future removal easier. Do not apply dielectric grease to the metal contacts.
- Insert the new coil pack until the spark plug boot is seated on the spark plug terminal. You may feel a “click” as the connection is made, but not always.
- Reinstall mounting hardware (screws, bolts, etc.).
- Reattach the coil pack connector.
- Reinstall any engine components that were removed to access the coil pack.
- Start the engine to verify the repair. If the engine does not start, check all the electrical connections, hoses and any other components that were removed.
What to Do After Changing Ignition Coil Parts
After changing ignition coil parts, let the engine warm up and go for a normal drive. The engine should run smoother than it did previously. If your car shakes after changing ignition coil components or the check engine light comes on, shut it off and retrace your steps. You will likely find a loose connector.
How Often to Change Ignition Coils
For most engines, there is no set mileage or set time for replacing ignition coils. If you are wondering how often to change ignition coils, the answer is pretty simple—when one wears out and starts causing a problem.
