All Haynes Digital Online Manuals are currently 50% off. They feature everything you love about our books in an instantly accessible digital online form, that you can use via any device with an internet connection.
This page is taken directly from our digital online manual 36059 for the 1997-2003 Ford F150 truck and 1997-2017 Ford Expedition/Lincoln Navigator, 2WD or 4WD with V6 or V8 gasoline engines, but it applies to many other Ford, Mercury and Lincoln vehicles that use the Ford "modular motor" like the Mustang, Crown Victoria, Grand Marquis, and Town Car. The ignition coil packs can be good for the life of the vehicle, but in extreme conditions like high humidity, rough roads, or off-road, the coils can crack and short or deliver a weak spark causing a misfire. It is recommended you replace the spark plugs every 60,000 miles or 5 years, and at that time inspect the coil packs and wiring for cracks or heat damage.
Ignition coils - check and replacement
Electronic Integrated (EI) Ignition system with coil packs
Check
- With the ignition off, disconnect the electrical connector(s) from the coil. Connect an ohmmeter across the coil positive (+) terminal and each negative (-) terminal (see illustration) . The resistance should be as listed below. If not, replace the coil.
Primary resistance 0.3 to 1.0 ohms
7.1 To check the primary resistance of the EI coil, connect the probes to the positive (+) terminal and each negative (-) terminal of the coil. The resistance should be the same for each check
- Connect an ohmmeter between the secondary terminals (the one that the spark plug wires connect to) of each coil pack (See illustration). The resistance should be as listed below. If not, replace the coil.
Secondary resistance 6.5 to 11.5 K-ohms
Note: Each coil pack is paired according to the companion cylinders. Be sure to check resistance with these designated terminals only:
4.2L V6 engines 1 & 5, 2 & 6, 3 & 4
4.6L engines 7 &4, 8 &2, 1 & 6 and 3 & 5
7.2 Check the coil secondary resistance by probing the paired companion cylinders via the spark plug wire terminals
Replacement
- Disconnect the negative cable from the battery.
- Disconnect the ignition coil electrical connector(s) from each individual coil pack.
- Disconnect the spark plug wires by squeezing the locking tabs and twisting while pulling. DO NOT just pull on the wires to disconnect them. Disconnect all of the spark plug wires.
- Remove the bolts securing the ignition coil to the mounting bracket on the engine (see illustration).
7.6 Remove the coil pack mounting screws (arrows) and lift it from the engine. 4.2L V6 is shown, V8 will be slightly different.
- Installation is the reverse of the removal procedure with the following additions:
A) Prior to installing the spark plug wire into the ignition coil, coat the entire interior of the rubber boot with silicone dielectric compound.
B) 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.
Electronic Integrated (EI) ignition with Coil Over Plug (COP) system
Check
Note: On 3.5L V6 engines, lift the fuel pump insulator up and off of the driver’s side valve cover to access the ignition coils.
- With the ignition off, disconnect the electrical connector(s) from each coil assembly. Connect an ohmmeter across the coil primary terminal (+) and the negative terminal (-) (see illustration) . The resistance should be as listedbelow. If not, replace the coil.
Primary resistance 0.55 ohms
7.8 Check the primary resistance of each coil over plug (COP) coil assembly at the electrical connector terminals
- Remove the COP assembly from the cylinder head. Connect an ohmmeter between the secondary terminals (see illustration) (the one that fits over the spark plug). The resistance should be as listed belo. If not replace the coil.
Secondary resistance 5,500 ohms
7.9 Check the secondary resistance of each coil over plug (COP) coil assembly between the electrical connector terminal and the spark plug terminal
Replacement
- Disconnect the negative cable from the battery.
- Disconnect the ignition coil electrical connector(s) from each individual coil. Mark each electrical connector with tape to prevent mix-ups during reassembly.
- Remove the bolt securing the ignition coil (see illustration) , then pull the coil from the cylinder head.
Note: On later model engines it may be necessary to first disconnect the electrical connectors for the fuel injectors to gain access to each ignition coil mounting bolt.
7.12 Remove the coil on plug (COP) mounting bolt and lift the assembly from the cylinder head
- Installation is the reverse of the removal procedure with the following additions:
A) Prior to installing the coil over plug (COP) assembly into the cylinder head, coat the entire interior of the assembly with silicone dielectric compound.
B) Connect each COP electrical connector to its correct coil and make sure they are tight and secure.
