How to Upgrade Ignition Coils

How to Upgrade Ignition Coils

The Ford overhead camshaft modular V8, commonly referred to as the “mod motor”, is an excellent engine with good efficiency and performance potential. These engines have been popular since the original version that began production in 1991, and it remains a popular platform for performance. There have been several iterations of ignition systems on the mod motor, with the earlier motors using a pair of quad-coil packs to the modern style that uses a coil-on-plug arrangement for the best possible ignition control. The coil-on-plug design was put into use in 1997 on the trucks, and 1999 on the cars.

Where a single coil system is convenient, the performance is lacking, especially in fuel injected cars. Coil-on-plug systems provide better fuel economy and performance, but swapping out coils definitely seems like more of a challenge. We brought a 2004 Mustang GT with the 4.6 liter V8 into the shop to show you just how simple it really is. The Mustang had been running a little rough and was lighting up the check engine sign. A quick scan with our code scanner, and we knew what the problem was – there were several cylinders with consistent misfires. Over time, the coil packs can weaken, not producing enough spark, add to that worn spark plugs, and the problems start mounting up.

A set of new NGK platinum spark plugs and all new Accel Supercoils were ordered from our local NAPA parts store. We could have gone with the factory-type coil, but the reality is that the Accel coil packs are actually cheaper than the OEM originals, and they provide a more powerful spark. This means the engine will run better, get better fuel economy (because it burns the fuel more completely), and have more power. Why not upgrade? Follow along as we show you how to upgrade ignition coils on our test vehicle.

First, the factory air inlet hose is removed.

First, the factory air inlet hose is removed.

The process of swapping the coils and spark plugs is fairly straightforward. It all starts by removing the air cleaner hose that runs from the airbox to the throttle body.

The factory coils are located under the fuel rails. Don't worry, the rails can stay on the engine.

The factory coils are located under the fuel rails. Don’t worry, the rails can stay on the engine.

This gives you access to the coils. The Mustang uses metric bolts, so make sure you have metric sockets. We used a 1/4”-drive ratchet with a long extension. The coils have a single hex-head screw holding it to the intake.

Give the coil a twist and then pull it out. Bend the head over to clear the fuel rail.

Give the coil a twist and then pull it out. Bend the head over to clear the fuel rail.

There is a long rubber boot on the bottom of the coil.

There is a long rubber boot on the bottom of the coil.

Grip the coil firmly and twist it while pulling it out of the socket. Only work on one cylinder at a time. You do not have to remove the fuel rails as some suggest, the coil boots will flex enough to get the coil out.

If the boot tears from the coil, use needle-nose pliers to yank the boot out.

If the boot tears from the coil, use needle-nose pliers to yank the boot out.

Sometimes, the coil will come off of the boot, if this happens, just use a pair of needle-nose pliers to yank the boot.

Be careful when removing the clip, they do break.

Be careful when removing the clip, they do break.

Now you can unclip the wiring harness.

You will need a long extension to reach to the spark plugs.

You will need a long extension to reach to the spark plugs.

The old spark plug uses a 5/8” socket. Pull it out.

Most of the time, the plugs are gapped correctly, but it is good to check.

Most of the time, the plugs are gapped correctly, but it is good to check.

We used a spark plug gapping checker to make sure the gaps were set to spec. We opened them up to .055” for performance. The factory Ford spec is .052” to .056”

With aluminum heads, it is important to coat the threads with anti-seize. Otherwise, the plugs would gall into the heads.

With aluminum heads, it is important to coat the threads with anti-seize. Otherwise, the plugs would gall into the heads.

The threads of the plugs were treated to a coating of anti-seize, and then threaded back into the head.

Don't forget to use the supplied dielectric grease on the coil tips.

Don’t forget to use the supplied dielectric grease on the coil tips.

The electrode portion of the coil needs some dielectric grease to keep it from corroding. This comes in the kit with the coil packs.

The new coils have substantially more voltage than the stock coils.

The new coils have substantially more voltage than the stock coils.

Next, the coil was dropped into the intake and seated onto the spark plug tip.

Reuse the original hardware to secure the new coils. Do not overtighten, the install can strip out quickly.

Reuse the original hardware to secure the new coils. Do not over tighten, the install can strip out quickly.

At this point, the original fastener is threaded in and tightened up. Not too much, the threads can strip out pretty easily.

If the original harness plug is broken, you can secure it to the coil with a ziptie.

If the original harness plug is broken, you can secure it to the coil with a ziptie.

Reconnect the wire harness. Repeat seven more times. Once finished, replace the air filter inlet hose.

All done! The touch of high-performance yellow peaking out from under the fuel rails adds just the right touch.

All done! The touch of high-performance yellow peaking out from under the fuel rails adds just the right touch.

Once all of the coils were installed, the job is done. The yellow coil packs look good under the hood, and the power was evident the second the engine fired up. The idle was smooth, the throttle response was more crisp, and on the street, the Mustang had more power than ever. While you won’t gain much horsepower, 10-15 % more spark energy makes a big difference in overall performance and fuel economy. The entire process took about 2 hours.

Check out all the maintenance parts available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how to upgrade ignition coils, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

about author

Jefferson Bryant

A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 4 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.

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