The Cadillac Northstar engine was originally introduced in 1992. The Northstar engine has been utilised in vehicles like the Deville, Seville and Eldorado models. The ignition-coil module is mounted to the top rear of the engine on the Northstar. There are four coils on the module, one for every two cylinders. The coil module is controlled by the ignition computer, and controls the spark in the engine. The current alternates between the coil-pack towers to provide spark to all eight cylinders.
Raise the bonnet of the Cadillac you are diagnosing. Visually inspect and locate the coil module on the top rear of the engine. The coil module contains four coil-packs on one large control panel.
Remove the two sparkplugs off of the first coil pack; remove from left to right. Set the sparkplug wires away from any moving parts, and do not touch the vehicle with any part of your body.
Ask an assistant or second person to turn the ignition key to the start position; crank the engine for no longer than three-second intervals. Instruct your assistant to count to three, and then immediately turn the ignition key to "off." Visually inspect for an electrical spark -- between the two spark plug towers that you exposed -- while the engine is turning. The coil is working correctly if the coil module has spark between the two modules. Replace the wires if the coil is properly working.
Repeat the same procedure with the second, third and fourth coil pack. Test the coils one at a time. Do not touch the vehicle at all during this test, due to the risk of electrical shock. Further diagnostic tests are required if a coil does not spark between the two towers.
Remove the suspect coil pack from the top of the module with a 1/4-inch-drive ratchet and socket, along with a 4-inch extension. Turn the coil-pack mounting bolts counterclockwise until they are completely removed. Pull the suspect coil pack off of the engine. Remove one of the good coil packs in this same manner, and switch the position of the two coil packs. Leave the plug wires off of the suspect pack, and place the plug wires onto the good module.
Ask your assistant to turn the engine key to "start" for no longer than three seconds. Turn off the key. Do not touch the vehicle, but visually inspect the suspect coil pack when the engine turns. The coil pack is bad if it does not spark in the new position. The ignition control module is bad -- and will need a replacement -- if the suspect coil pack sparks.