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How do I Check a Jeep Grand Cherokee Coil Pack?

by Dustin Thornton

The 2000 through 2004 Jeep Grand Cherokee L6 4.0L 6-cylinder engines employ a coil pack as part of the ignition system. A coil pack converts the energy from your 12-volt battery into the 35,000 plus volts needed to fire the spark plugs. A bad coil pack can cause the engine to misfire. The coil pack has three separate ignition coils bundled into one unit and you must replace the entire unit if one of the coils is faulty. You can test the coil pack in your Jeep Grand Cherokee by measuring the electrical resistance of the coil pack with an ohmmeter.

Put on your safety glasses and open the hood. Disconnect the negative cable from the battery and place it out of the way so that it will not make contact with the battery terminal while you work.

Locate the coil pack. The coil pack is a long black unit, bolted directly on the cylinder head on the left side of the engine. The coil pack attaches directly to the spark plugs.

Remove the four coil pack mounting bolts using a ratchet.

Pry the coil pack away from the engine head. Grasp each end of the coil pack and work it back and forth until you can remove the coil pack boots from the spark plugs.

Lift the coil pack up slightly until you gain access to the electrical connector on the back side of the unit. Depress the clip on the electrical connector and unplug it from the coil pack. Remove the coil pack.

Place the coil pack on a flat surface.

Turn on your ohmmeter and set it to the 20,000 ohms range.

Touch the ohmmeter leads to the connectors in the first spark plug boot. Your meter should read from 6,000 to 30,000 ohms. Repeat this on each spark plug boots. Replace the coil pack if the measurement falls outside of this range.

Set the ohmmeter to the 10 ohms range. Touch the center prong on the electrical connector with one of the leads and the first spark plug boot with the other. Your meter should read less than 2 ohms. Repeat this while touching the second lead to each spark plug boot. Replace the coil pack if the measurement is higher than 2 ohms.

Replace the coil pack with a working coil pack, if necessary. Reinstall it following the removal procedure in reverse.

Items you will need

About the Author

Dustin Thornton has been writing since 2003. He has served as a newspaper columnist for the "Troy Tropolitan" and a contributor to various websites. Thornton received a partial scholarship for an outstanding essay in 2003. He has a Bachelor of Science in business administration from Troy University.

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