How to Check the Coil Pack on a Ford Engine

Written by lee sallings
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The Ford distributor-less ignition system uses coil packs to fire the spark plugs of the engine. Each coil in the coil pack is paired with two corresponding engine cylinders so that when the coil fires, it is firing one cylinder in the pair during the power stroke, and one cylinder of the pair during the exhaust stroke. Late model engines use a "Coil On Plug" design that uses individual coils mounted directly on the spark plug. Test both types of coils the same way.

Skill level:
Moderately Challenging

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Things you need

  • Automotive circuit tester
  • Digital volt/ohmmeter
  • Wiring diagram
  • Service manual

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Instructions

  1. 1

    Test for power to the coil by disconnecting the wiring harness plug from the coil then, with the key in the run position, use the circuit tester to check for power at the coil wiring harness connector. If no power is present at the connector, check for a blown fuse, or fusible link at the power distribution block (fuse block). Fuse locations are outlined in your service manual and owner's manual, but it is a good idea to check all the fuses in the power distribution block.

  2. 2

    Test for a pulsing ground to the coil on the wiring harness connector. The ignition module turns the primary windings of the coil off and on to trigger the secondary windings. This is done by grounding and then un-grounding the negative (ground) side. Use the circuit tester to verify that this is happening, at the wiring harness connector, when cranking the engine.

  3. 3

    Refer to the service manual for the resistance specifications on your specific Ford vehicle. Test the resistance across the primary windings with the digital volt/ohmmeter. Resistance readings of infinite or 0 ohms indicate an open circuit or shorted circuit respectively. Use the digital volt/ohmmeter to test the resistance of the secondary circuit as well. Compare the test results to the specifications in the service manual.

  4. 4

    Test secondary ignition strength with a spark plug tester. Plug the tester into the coil wire and set the tester for "E" on the scale. Crank the engine, and observe the spark quality. A weak, thin spark indicates a weak coil. A good spark will be large and bright red or bright blue in colour.

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