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How to Test a Jeep Coil Pack

by Dustin Thornton

Some vehicle ignition systems use coil packs to convert the power from the 12-volt battery in your car to the necessary 35,000 volts required to fire spark plugs instead of a distributor and rotor assembly. Often called a distributorless ignition system, the Jeep L6 engine employs coil packs. Bad coil packs can cause engine misfires, lack of power and faulty starting -- much the same as bad distributors. If you suspect that you have a faulty coil pack, you can remove it and test it with an ohmmeter.

Put on a pair of safety glasses to protect your eyes.

Open the hood and loosen the bolt on the negative battery cable. Remove the negative battery cable from the negative battery terminal.

Remove the coil pack mounting bolts with a wrench. There are four mounting bolts -- one in each corner of the coil pack. The coil pack is located on the left side of the engine, bolted onto the cylinder head. It connects directly to the engine spark plugs.

Work the coil pack back and forth until you free it from the spark plug slots. Lift it up slightly and disconnect the electrical connector located on the back of the coil pack.

Remove the coil pack from the engine and set it on a clean work surface.

Activate the ohmmeter and set it on 20,000 ohms.

Press both of the ohmmeter leads against the connections inside of each spark plug boot on the coil pack, one at a time (six total). Do not let the leads touch each other or else you will receive a faulty rating. The ohmmeter rating should fall between 6,000 and 30,000 ohms. If the ohmmeter rating is above or below this range, replace the coil pack.

Change the ohmmeter setting to 10 ohms.

Hold one lead in your left hand and one lead in your right hand. Press the left ohmmeter lead against the center prong inside the electrical connector on the back of the coil pack. Press the other lead against each of the spark plug boots, one at a time. The ohmmeter rating should be below 2 ohms. If the ohmmeter rating is above 2 ohms, replace the coil pack.

Follow the removal instructions in reverse the reinstall the coil pack.

Tip

  • If even one of the coils on the coil pack is bad, you must replace the entire unit.

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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