Mercury FOTZ-12029-A Coil Assembly - Ignition

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Check the ignition coil by first turning off the ignition and disconnecting the electrical connector(s) from the coil. Connect an ohmmeter across the coil positive (+) terminal and each negative (-) terminal to check the primary resistance of the ignition coil. The resistance should be the same for each check. Then, connect an ohmmeter between the secondary terminals of each coil pack. If continuity does not exist, replace the coil. The ignition coil pack(s) contains three separate coils on V6 models and four separate coils on VB models. Each coil is paired with its companion cylinder. Be sure to check resistance across the appropriate secondary terminals for each coil. To replace the ignition coil pack, disconnect the cable from the negative terminal of the battery. Check to see if all the spark plug wires are numbered. If not, clearly label each plug wire with a piece of tape marked to match the numbers listed on the coil terminals. Then disconnect all the spark plug wires by squeezing the locking tabs and twisting while pulling upward. Do not pull on the wires. Disconnect the ignition coil pack electrical connector. Remove the screws that secure the coil pack to the coil mounting bracket. Installation is the reverse of the removal procedure with the following additions: Before installing the spark plug wire connector into the ignition coil, coat the entire interior of the rubber boot with silicone dielectric compound. Insert each spark plug wire into the proper terminal of the ignition coil. Push the wire into the terminal and make sure the boots are fully seated and both locking tabs are engaged properly.To replace the ignition coil and mounting bracket, detach the radio interference capacitor (if equipped) from the coil mounting bracket. On 4.0L pushrod engines, detach the plastic clip that secures the fuel injection wiring harness to the coil mounting bracket. Then remove the bolt holding the air conditioning hose to the intake manifold plenum. Move the air conditioning tube enough to provide working access to the upper coil mounting bracket bolts. Remove the bolts securing the ignition coil mounting bracket to the engine. On 4.0L SOHC engines, the ignition coil mounting bracket is welded to the valve cover, and therefore unnecessary to remove for access to other components. On 5.0L engines, disconnect the hoses and wiring from the EGR vacuum solenoid, then remove the bolts securing the ignition coil mounting bracket to the engine. Installation is the reverse of the removal.

Disconnect the cable from the negative terminal of the battery. Check to see if all the spark plug wires are numbered. If not, clearly label each plug wire with a piece of tape marked to match the numbers listed on the coil terminals. Then disconnect all the spark plug wires by squeezing the locking tabs and twisting while pulling upward. Disconnect the ignition coil pack electrical connector. Remove the screws that secure the coil pack to the coil mounting bracket. Installation is the reverse of the removal procedure.

To replace the coil, first disconnect the negative cable from the battery. Then, disconnect the ignition coil electrical connector(s) and spark plug wires. Remove the bolts securing the coil to the mounting bracket. Install the new coil, ensuring that the interior of the rubber boot is coated with Silicone Dielectric Compound. Properly insert the spark plug wires into the terminals. Finally, reinstall the radio ignition interference capacitor if applicable.

Checking the primary and secondary coil resistance is crucial to ensure the proper functioning of the ignition system.

Each coil should be inspected for any cracks, damage, and carbon tracking.