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Jeep Cherokee 1984-1996: How to Replace Spark Plugs and Wires

It is easy to change the plugs and wires in a Jeep Cherokee. Fortunately, the 4.0 isn't picky with plugs, so any brand of your choosing will be fine and it will run great.

By Mark Garrett - September 4, 2015

This article applies to the Jeep Cherokee XJ (1984-1996).

Spark plugs and plug wires are some of the easiest maintenance items on your Jeep. With the straight six, it is easy enough to get to and change them. Your choices for plugs range from the stock type Champion to triple platinum NGK. Spark plug wires have the same range. Factory Mopar are OK and go up to 9mm performance sets. Which ever you choose, there are some basic things to do to make the results better. This is pretty easy, so let's save some bucks!

Materials Needed

  • 3/8" ratchet, extension, and universal joint
  • 5/8" spark plug socket
  • Gap gauge
  • Anti-seize compound
  • Dielectric grease
  • Spark plug wires (1 set)
  • Spark plugs (6)

Before we get started, there is vitally important information to know: the firing order. The firing order for all 4.0 liter Jeeps is seen in Figure 1. All you have to do is connect the numbers from the distributor cap to the spark plugs. Do it exactly like the diagram and you will be set.

Figure 1. Jeep 4.0 firing order.

Pro Tip

This is an ideal time to replace the distributor cap and rotor. If you do, you will spend a couple bucks more and you should get good ones with brass terminals. Remove the old cap from the distributor, put the new rotor and cap on, then put the old wires in the exact same spots.

Step 1 – Lay out the new plug wires

If you purchase the exact fit replacement plug wires, they will look similar to your originals. Lay all of them out and arrange from shortest to longest. Now you can match the ones you remove to the originals.

Figure 2. Spark plug wires.

Step 2 – Remove spark plugs from package

Once you decide what spark plugs you want, remove them from the package and lay them out with the wires. Check the gap; although, they should be correct from the factory. The gap is .035". Your Jeep came from the factory with Champion plugs. They require a washer to seal to the head. Put this washer on the plugs now.

Figure 3. Typical Champion 4.0 plugs.

Step 3 – Change plugs

Start with plug number 1. Remove the plug boot. Put your plug socket on the plug and break it loose with the ratchet. Put anti-seize paste on the threads and thread into the head by hand. Tighten to 27 ft/lbs. That is as tight as it needs to be. Replace the wire for now. Continue with all six.

Figure 4. Anti-seize compound.

Step 4 – Replace plug wires

Start with number 1 again and remove the plug wire. Match it to the new ones by matching the length and boot style. Before reinstalling the wires, coat the inside of both boots with dielectric grease to seal them. Continue with the other five, plus the coil wire. If there are plastic wire holders on the old ones, reinstall the new wires in them to not only secure them, but also to keep any cross fire from happening.

Figure 5. Uncap the wires from the distributor.

Pro Tip

Dielectric grease seals the boots and also makes getting them off easier.

Featured Videos: How to Replace Spark Plugs and Wires

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