Buy Cadillac DeVille Ignition Coils

The ignition coil turns your car battery's low voltage into the high voltage that fires each spark plug. On the Cadillac DeVille, a healthy coil keeps the 4.6-liter Northstar V-8 smooth and strong; a weak coil causes misfires, poor gas mileage, and a glowing check-engine light. (Wikipedia, Cars.com)

Inside the coil are two copper windings around an iron core. When current flows, a magnetic field builds and then collapses, sending up to 40,000 volts to the spark plug to ignite fuel. Learn more in this simple explainer on the ignition coil. (Wikipedia)

• 1995-1999 DeVille: Two large coil cassettes bolt to the top of each valve cover. Each cassette holds four individual coils. (Cadillac Forums)
• 2000-2005 DeVille: Cadillac switched to revised cassettes with coil-on-plug leads and roller cams for better emissions. (Cadillac Forums, Wikipedia)
• Early 1990-1993 4.9-L models use a separate coil pack near the front of the engine.

• Rough idle or shaking at stoplights. (Cadillac at Service, Cars.com)
• Sudden drop in power when accelerating. (Popular Mechanics)
• Flashing check-engine light with code P0300 (random misfire) or specific cylinder codes like P0306. (JustAnswer, YouTube)
• Hard starting after the car sits overnight. (Cadillac Forums)

1. Swap-and-see: Move the suspect coil to another cylinder; if the misfire follows, the coil is bad. (Popular Mechanics)
2. Resistance check: Compare primary and secondary resistance with an ohmmeter; coils should be within 10 percent of each other.
3. OBD-II scan: A budget scanner will flag misfire codes and show live data. (Popular Mechanics)

A detailed walk-through video for the 2001 DeVille makes the job easy-watch it here. (YouTube)

• Disconnect the negative battery cable.
• Remove plastic beauty cover and AIR tubes. (Cadillac Forums)
• Unplug the six-pin ICM connector on the cassette. (Cadillac Forums)
• Undo the five 10 mm bolts holding the cassette; lift straight up.
• Swap in the new coil cassette; tighten bolts to 89 in-lb (10 N·m). (Scribd)
• Add a dab of dielectric grease to each rubber boot before re-installing.

• Replace spark plugs every 100,000 miles to reduce coil strain. (Cars.com)
• Keep the valve-cover area clean; oil and moisture shorten coil life. (Popular Mechanics)
• Use dielectric grease on boots to block moisture and ease future removal. (Scribd)

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Enthusiasts sometimes install aftermarket high-energy coils for a stronger spark. A hotter spark can smooth idle and help fuel burn cleaner in older Northstar engines, but it will not fix underlying mechanical issues such as head-gasket leaks. Always match coil impedance to the engine control module. (Scribd)

High voltage can shock. Always pull the key, wait five minutes, and wear gloves before touching the cassette. Dispose of old coils at a local recycling center; they contain copper and oil-based resin. (Wikipedia)

A failing coil lets raw fuel enter the catalytic converter, overheating and damaging it-one reason "replace ignition coils" ranks in the top ten check-engine fixes nationwide. (Cars.com, Cars.com)

Q: What years of DeVille use the Northstar coil cassette?
A: From 1995 through 2005, every DeVille with the 4.6 L Northstar uses a coil cassette, with a design update in 2000. (Cadillac Forums, Cadillac Forums)

Q: Can I drive with a bad spark coil?
A: You can, but you should not. Unburned fuel can ruin the catalytic converter and lower gas mileage fast. (Cars.com)

Q: Why do I get code P0306 after rain?
A: Moisture collects around the rear cassette; water weakens the cylinder 6 coil. A bead of dielectric grease around each boot helps seal it. (YouTube, Cadillac Forums)

Q: Do I have to change all the coils at once?
A: No. The cassette lets you unbolt and swap a single coil if only one fails. Still, many owners replace the whole cassette after 150 k miles for peace of mind. (JustAnswer)

Q: Is the coil covered in any recall?
A: No coil-specific recalls exist; most DeVille recalls focus on fuel-rail and cooling issues, not the ignition cassette. (NHTSA)

Q: Will premium fuel extend coil life?
A: Not directly. The 2000-up Northstar can use regular gas, but premium helps prevent knock, which lowers cylinder temps and may reduce coil stress over time. (Wikipedia)

Q: What tools do I need for replacement?
A: A 10 mm socket, a torque wrench, dielectric grease, and safety gloves are enough for most driveway jobs. (YouTube)

Q: How long does the job take?
A: A first-timer usually finishes in about one hour per cassette. Experienced DIYers can swap both banks in 30 minutes. (YouTube)

Q: What other parts should I inspect while I'm there?
A: Check spark plugs, valve-cover gaskets, and the AIR tubes for leaks; fixing them together saves labor and avoids double work. (Cadillac Forums)