How to Test Ford Coil Packsby Paul Vaughn
Late model Fords are equipped with coil packs rather that the old style individual coils for each cylinder. These coil packs are solid state units that transmit electricity from the Ford's computer control module to the ignition wires and then to the spark plugs, allowing them to fire in a precise order. Coil packs are fairly simple to diagnose with these few easy steps.
Start the vehicle and note the running condition of the cylinders. Is the engine running smoothly or is the engine missing on one or more cylinders?
Locate the coil pack for your Ford. They are usually located near the right fender well.
Check that each plug wire is firmly plugged into the coil pack and in the right order. The number of each wire is stamped next to the connection terminal.
Inspect each wire connection for discoloration or damaged wires.
Use your volt ohm meter to check wire continuity by touching the ground lead to a suitable ground lead and using the red probe lead to check for an ohm reading. Ohm readings should be 1.5V for primary wire inputs and 8,000 to 9,000 for secondary wires. Infinite ohms reading (the meter will have a zero reading) indicates an open circuit somewhere in the wire harness that will need to be located to its source and the wire replaced.
Replace the coil pack if all recommended steps have been taken, everything checks out properly yet the spark plugs are still not firing correctly.
- Visual inspection should tell you everything you need to know for this procedure. Solid state ignitions do not have moving parts that can be repaired or replaced. The coil is replaced as a unit.
Things You'll Need
- Digital volt ohm meter
- Electrical contact grease
- The ignition system generates extremely high voltage that can damage test equipment and harm the technician. Be sure to follow the steps, as outlined, to prevent any problems.
Paul Vaughn has worked in the auto and diesel mechanics field for 10 years and as public school automotive vocational teacher for five years. He currently teaches high school auto tech, covering year model vehicles as old as 1980 to as new as 2007.