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Jeep Wrangler JK: How to Replace Spark Plugs

Although many manufacturers are setting spark plug maintenance intervals near 100,000 miles, most enthusiast prefer to swap spark plugs more regularly. With spark plugs being relatively inexpensive, there are absolutely no downsides to replacing them as part of your regular maintenance regimen.

By Joseph Coelho - November 17, 2015
Contributors: JeepFan & DSJeeps

This article applies to the JK Jeep Wrangler (2007-Present).

Spark plugs are key components of any gasoline internal combustion engine. These small devices deliver electric current from the ignition coil(s) to ignite the air/fuel mixture inside of the combustion chambers. While spark plugs have proven to be quite robust and can last thousands of miles without the need for replacement, modern ignition systems have become quite sensitive to worn spark plugs. As spark plugs age, material from the electrode erodes and creates a larger gap for the voltage to jump across. Excessive gap has a tendency to place a strain on plug wires and ignition coils because this larger gap creates a higher resistance that must be overcome to create a spark. Spark plugs can also experience carbon buildup or insulator cracking, all of which can lead to engine misfiring or premature coil failure. Proper spark plug maintenance will ensure your ignition system is performing at its best to maximize combustion efficiency. This article will outline the procedure for replacing spark plugs in 2007 to present JK Jeep Wrangler models.

Materials Needed

1/4" and 3/8" drive ratchets
5/8" spark plug socket
Various extensions (with one being at least 12" long)
8mm and 10mm sockets
T20 Torx driver
Torque wrench
Universal joint (swivel adapter)
Spark plug gapping tool or feeler gauges
Screwdriver
Dielectric grease
Anti-seize paste (optional)

Buying Replacement Spark Plugs

Generally, it is best to use OEM equivalent spark plugs in your Jeep. Aftermarket spark plugs can be less expensive, but they are often not made to the exacting standards as the spark plugs fitted from the factory. OEM plugs usually have a specific electrode design and material quality that is best suited for the engine. This is not to say there are no exceptions to this rule, but more often than not, individuals experience various engine and ignition system problems by using "exotic" aftermarket spark plugs instead of the tried and true originals.

2007-2011: Champion Part #RE14PLP5
2012+: Champion Part #RER8ZWYCB4

This how-to will cover spark plug replacement for both 2007 to 2011 3.8L EGH V6 engine and 2012+ 3.6L Pentastar V6 engine. For 2012+ models, the step-by-step instructions are below.

2007-2011 3.8L EGH V6 Engine

Step 1 – Replace bank 2 spark plugs

The 2007 to 2011 Wranglers equipped with the older 3.8L V6 engine allows for easy access to the driver's side spark plugs.

Locate the three spark plug wires on the driver's side of the engine. With a twisting motion, remove each spark plug wire from its companion spark plug. The spark plug wires are typically numbered to prevent them from getting mixed up.

Figure 2. Spark plug wires leading to spark plugs.

Using a 3/8" drive ratchet with an extension, universal joint adapter, and 5/8" spark plug socket, remove the spark plugs.

Figure 3. A long extension and universal joint allows for easy reach of the spark plugs.
With the old spark plugs removed, prep the new spark plugs by checking the electrode gap with a gapping tool or feeler gauge. The spark plug gap specification for 2007 to 2011 models is .050". Do not assume the plugs are ready to run out of the box. Improper spark plug gap can lead to rough running conditions.

Figure 4. Checking and adjusting spark plug gap.
Place the new spark plug into the spark plug socket, making sure it is firmly held in place, and then lower it into its respective position in the cylinder head. Thread the spark plug carefully into the cylinder head and tighten it to 12 ft/lbs. Repeat for each plug.

Figure 5. A 3/8" drive torque wrench can be used to tighten spark plugs.

Pro Tip

While Jeep does not suggest anti-seize paste on the threads of the spark plugs, some individuals opt to apply it, especially if your Jeep is used for off-road purposes.

Apply a thin film of dielectric grease to the spark plug boots before installing them onto the spark plugs. A small "click" can be heard and felt when the spark plug boot is firmly seated on the spark plug.

Figure 6. Application of dielectric grease on plug boots.

Step 2 – Replace bank 1 spark plugs

To gain access to the passenger's side spark plugs, a few components must first be moved.

Disconnect the bank 1 spark plug wires (1, 3, 5) from the coil pack. It is recommended you label them if your wires are not already labeled.
Remove the spark plug wires from the passenger's side spark plugs and remove the heater hose retaining strap from the valve cover. Also, remove the vent hose from the valve cover.
Remove the plastic spark plug wire tray from its mounting point on the valve cover. Maneuver the spark plug wires out from behind the engine and remove them from the engine bay. Pay close attention to their routing, as it will allow for proper installation after the new spark plugs are installed.

Figure 7. Spark plug tray mounting/Spark plug tray and wires removed.
With the spark plugs now accessible, proceed with replacing them as in Step 1.

Figure 8. New vs old spark plug.
With the new spark plugs installed, re-route the spark plug wires and tray back into place. Install the plug wire tray, heater hose strap, and valve cover breather in their respective positions on the engine. Attach the spark plug wires to the spark plugs and coil pack using a bit of dielectric grease on the boots and making sure they properly click into place.
Start the engine and ensure the vehicle is running smoothly. If the engine stumbles or has a misfire, check that all plug wire connections are properly attached.

2012+ 3.6L Pentastar V6 Engine

Spark plug replacement is much more in-depth on 2012+ Wranglers, as the intake plenum must be removed to access the driver's side spark plugs. Follow the steps below for the replacement procedure.

Step 1 – Replace bank 1 spark plug

The passenger's side spark plugs are the easiest to access and can be quickly replaced without a fuss.

Open the hood and remove the plastic engine cover. The cover simply pops off with light pressure.
Using a 10mm socket or wrench, disconnect the negative (black) battery cable.

On the passenger's side of the engine, unclip the vacuum lines hold-downs and slide the vacuum lines out of the way.

Figure 10. Releasing vacuum line from hold-down.
Using a 10mm socket and ratchet, remove the coil hold-down screws from each coil. With the screws removed, the coils can be disconnected from their companion spark plugs by lifting straight up. In some cases, twisting and wiggling the coil can aid in removal. If replacing the coils as well, disconnect the electrical plugs that lead to each coil.

Figure 11. Removing coil hold-down screws.
If you have access to compressed air, it is a good idea to blow out the spark plug access hole to prevent any dirt or debris from falling into the engine when the spark plug is removed.

Figure 12. The spark plug is now visible with the coil removed.
Using a ratchet with a 12" extension and 5/8" spark plug socket, remove the spark plugs.

Figure 13. Spark plug removed.
Before installing the new spark plugs, ensure they are correctly gapped at .043".
Place a new plug into the spark plug socket and thread it into the cylinder head. Torque to approximately 13 ft/lbs. Repeat for remaining bank 1 spark plugs.

Figure 14. Spark plug installation.
Using a bit of dielectric grease, lubricate the boot of each coil before reinstalling them onto the new spark plugs. Be sure to install the coil hold-down screws and reconnect the electrical harness to each coil if they were disconnected.

Figure 15. Light film of dielectric grease on coil boot.
Reattach the vacuum line hold-down clips.

With bank 1 finished, proceed with plenum removal.

Step 2 – Replace bank 2 spark plug

The most difficult part of the spark plug change procedure on 2012+ Wranglers is the removal of the intake plenum. The plenum must first be removed to access the bank 2 (driver's side) spark plugs.

With an 8mm socket, loosen the three long fasteners located on the topside of the plenum. These screws will stay in the plenum, but can be slid upwards when they are fully loosened.

Figure 16. Long plenum screws slid upwards.

Using a small screwdriver or pry bar, remove the two flat plastic plugs on the topside of the plenum near the firewall. Slide the foam back to reveal two additional screws. Removing these screws with a 10mm socket will allow for the foam piece and mounting tabs to be removed.

Figure 17. Plastic plugs, screws, and foam piece removal.

Remove the two rubber vent lines from the front side of the plenum. Using a 10mm socket, remove the the nuts securing the heater core hard lines in place. Also, disconnect the three rubber breather hoses from the side of the plenum by simply sliding them apart.

Figure 18. Plenum vent lines, heater line hold-down, and breather hoses.
With a T20 Torx driver, remove the four lower plenum screws.

Figure 19. Lower plenum screws.
Remove the heater line bracket using a 10mm socket. With the bracket removed, unclip the rubber hose on the opposite side of the heater lines.

Figure 20. Heater line bracket and rubber hose clip.
Disconnect the intake tube from the throttle body/airbox by first disconnecting the air temperature sensor located in the intake tube. Remove the two bolts securing the intake tube to the fan shroud using a 10mm socket. Disconnect the intake tube clamps at the airbox and throttle body before sliding the intake tube out.

Figure 21. Intake tube removal.
Disconnect the MAP sensor and remove the small breather hose (located just beneath MAP sensor plug).

Figure 22. Disconnecting MAP sensor harness.
There are four remaining plenum fasteners on the driver's side of the plenum. Using a 10mm socket, remove the four nuts.

Figure 23. Remaining plenum fastening nuts.

Remove the wiring clips near the the throttle body using a screwdriver or small pry bar.

Figure 24. Plenum wiring clips near throttle body.
Unplug the throttle body wiring harness and remove the plenum/throttle body assembly from the engine.

Figure 25. Plenum removed from engine.
Set the foam pad covering the coils aside. You now have access to the coils and spark plugs. Remove the coils and replace the spark plugs as was completed in Step 1.

Figure 26. Coils and spark plugs now accessible.
Once the new spark plugs are coils are in place, consider replacing the rubber plenum gaskets before installing the plenum. The rubber gaskets tend to harden and crack, so it is a good idea to have gaskets on hand.

Figure 27. Plenum gasket (Mopar Part # 05184331AC).
Reassembly is the reverse of the procedure outlined above.
Reconnect the battery, install the engine cover, and proceed with starting the car to ensure it is running properly.

Figure 28. Start the car to ensure a smooth idle with no misfires.