How to Change Spark Plugs on Your Jeep 4.0L

If you own a Jeep and are experiencing rough idling, misfires, or a decrease in fuel efficiency, it may be time to replace your spark plugs. Spark plugs play a crucial role in the ignition process of your engine, providing the necessary spark to ignite the air-fuel mixture. Over time, spark plugs wear out and need replacement to ensure optimal performance. In this comprehensive guide, we will walk you through the step-by-step process of changing spark plugs on your Jeep. So let’s dive in and learn how to change spark plugs on your Jeep like a pro!

Getting Back to Basics

We all enjoy trying to come up with a decent write-up on lift kit installs or front bumper installations, but you still end up back at the basics when it comes to the engine. Sometimes, even the basics can be overwhelming to the novice tuner. With the current growth of offroading and the influx of new Jeepers, both guys and gals, and with Jeeps coming out of the factory plenty capable as they are…..well let’s just say that there is a lot of inexperienced novice Jeepers out there. So this is for them, and if any of you more experienced folks out there get something from this, even better.

Changing spark plugs ain’t that hard. Right? No, not really, especially when your rig is newer. Many years ago, I learned this procedure with plug swaps. There will be a few extra steps taken that, in the long run, can make that plug change 100,000 miles from now go smoothly. This installation pertains to the 4.0 L6 engine.

Tools and supplies for spark plug installation

To get started with changing the spark plugs on your Jeep, you’ll need a few tools and materials. Here’s a list of what you’ll need:

• Socket wrench
• 6″ extension
• 13mm socket
• 5/8″ Spark plug socket
• New spark plugs (make sure they are compatible with your Jeep’s make and model)
• Feeler gauge
• Anti-seize
• Dielectric grease
• paper towels or rags
• I use but didn’t show a pic……flex knuckle

Pick your poison

There are numerous brands of spark plugs available. Many different flavors and prices. I won’t recommend any particular brands. I will say that, based on my experience, the expensive, gimmicky ones are just that – expensive and gimmicky – but I haven’t seen any true gains from them. Also, avoid cheap imported “X” brands. They’re not consistent at all. For my swap, I picked up Champion Iridium Spark Plugs on Amazon.

 

Preparing Your Jeep

Before diving into the spark plug replacement process, it’s essential to prepare your Jeep. Follow these steps:

1. Park your Jeep on a flat surface and engage the parking brake.
2. Allow the engine to cool down completely to avoid any burns.
3. Open the hood and locate the battery. Disconnect the negative terminal to prevent any electrical mishaps during the process.

What’s the Gap?

Installing new plugs without checking and correcting the gap is just a waste of time, effort, and money. The gap is essential for maintaining consistency in fuel burn within the cylinders. Running too narrow of a gap and the flame kernel will get squashed, and doesn’t give a good burn. Too broad a gap causes misfires. The spark may decide to jump to the cylinder wall or piston dome, either of which can cause hot spots. Hot spots inside the cylinder burn off the incoming fuel charge before the plug fires.

The recommended gap for Jeep Wrangler TJ is .035 or 35 thousandths of an inch.

You want the gauge to slide between the electrode and the ground with a little resistance. If it’s too wide, tap the end gently to close. Too narrow, then just pry up on the ground to open. Gap all 6 and set them aside. If you drop any, check the gap again and ensure the ceramic hasn’t broken.

Open that hood! – Removing the old spark plugs

I like to lay the hood back against the roof. If it’s windy, secure it in place with a bungee cord so that it can’t close on you. You can use the prop, but I find that it makes getting to the rear plugs difficult.

If you have an earlier model built prior to 2005, you will notice a couple of major changes have been made. Gone are the distributor and plug wires, replaced by a distributorless ignition and spark plug power rail. There are many bonuses to this new setup. All it used to take was water on the wires or a hairline crack in the distributor cover to leave you stranded. No more having to pay attention to which wire came from which spot on the cap.

At this point, if you have a model with plug wires, I recommend changing only one plug at a time to prevent confusion with the wire order.

If you have the power rail, it will need to be removed so that you can access the spark plugs. There are 2 bolts at the front and 2 at the rear. Use the 13mm socket wrench to remove these.

Watch out for the red wire on the alternator, which is hidden just under the socket wrench. Hit that by accident, and you could weld the wrench to it.

There is a bolt just under the tube from the airbox to the Throttle Body. You can either remove the tube or use a wrench or swivel to loosen and remove the bolt. After removing the 4 bolts, grab the power rail from both ends and wiggle, and pull until it comes loose. It can fight a bit until the suction of the boots releases from the plugs. It’s wired into a harness and won’t go anywhere, so just let it sit out of the way.

Use the 5/8″ spark plug wrench and remove the old plugs. There is a difference between a spark plug socket and a deep well socket. Spark plug sockets are tapered inside to help support the plug and a rubber grommet to help center and hold the plug from dropping out when you turn the socket with the plug end down. It’s amazing how easy you can to break the ceramic with a standard 5/8″ deep well socket.

Inspecting the Spark Plugs

Inspecting the old spark plugs can provide valuable insights into the engine’s condition. Here’s what to look for:

1. Check the electrode: A worn-out spark plug will have a rounded or eroded electrode. Ideally, the electrode should have a flat surface and a gap according to your Jeep’s specifications.
2. Examine the insulator: Inspect the insulator for any signs of damage, such as cracks or excessive carbon buildup.
3. Check the color: A normal spark plug should have a light tan or grayish color. If the spark plug is covered in black soot, it indicates a rich fuel mixture.

Anti-Size Does Just like Says

I learned many years ago that using these two products properly can make servicing vehicles a pleasure, rather than a pain.

It prevents threads from seizing or freezing, allowing the bolts to be removed more easily in the future. I put a very small dab on the spark plug threads before threading them in.

Take some care and hand-thread the plugs in

Don’t cross-thread the plugs. Cross-threading is easy to do when working in tight spaces at odd angles. So thread them in till they stop. There are 2 different methods of seating plugs. This depends on how they’re made. Some use a washer or gasket. You only tighten these a 1/2 turn with a socket wrench from the point where they’re hand-seated into the head. The other type has only a bevel, and this type requires only 1/16 of a turn past hand tight with a wrench.

The next important step is to put a small amount of dielectric grease or tune-up grease into the spark plug boots. Dielectric Grease is great stuff. It’s made specifically for electrical connections that are subjected to extreme conditions or elements. It will keep out moisture and promote conductivity. It also keeps the boots from overheating. This will be important in 30,000 miles when you need to reinstall new plugs again. It makes the boots come off nicely without tearing.

Push the rail back onto the spark plugs. Then, apply a dab of anti-seize to the rail bolts and thread them back in. The hand tightens, and the torque is set to 20 ft-lbs.

Well, that’s about it, you’re done with this. I want to stress the importance of using Anti-Seize and Dielectric Grease. It will really make the following change potentially go a lot easier. Nothing worse than having a torn plug boot, or having a wire tear out, or one of the plugs frozen in.

Replacing the Spark Plug Wires

While changing the spark plugs, it’s a good idea to replace the spark plug wires as well. Here’s how to do it:

1. Start with the first spark plug wire. Firmly grip the boot at the spark plug end and twist it to break the seal.
2. Gently pull the spark plug wire away from the spark plug.
3. Repeat this process for all the spark plug wires.
4. Install the new spark plug wires in the reverse order, ensuring each wire is securely connected to both the spark plug and the distributor.

Reassembling and Testing

With the new spark plugs and wires installed, it’s time to reassemble everything and test your Jeep. Follow these steps:

1. Reconnect the negative terminal of the battery.
2. Replace the engine cover if you removed it earlier.
3. Start your Jeep and listen for any abnormal noises.
4. Take your Jeep for a short test drive to ensure smooth acceleration and no misfires.

Conclusion

Changing the spark plugs on your Jeep is a task that can significantly improve your vehicle’s performance and fuel efficiency. By following the steps outlined in this guide and taking the necessary precautions, you can confidently change the spark plugs yourself. However, if you’re unsure or uncomfortable with the process, it’s always best to seek professional assistance. So go ahead and give your Jeep the care it deserves, enjoying a smoother and more efficient driving experience!

FAQs: Spark Plugs for Jeep

How often should I change the spark plugs on my Jeep?

It is generally recommended to change spark plugs every 30,000 to 50,000 miles,
or as specified in your Jeep’s owner’s manual. However, if you notice signs of wear
or decreased performance, it’s best to change them sooner.

Can I use any type of spark plugs for my Jeep?

No, it’s important to use spark plugs that are specifically recommended for your
Jeep’s make and model. Using the incorrect spark plugs can result in poor performance
and potential engine damage.

What are the signs of worn-out spark plugs?

Some common signs of worn-out spark plugs include:

• Rough idling
• Engine misfires
• Reduced fuel efficiency
• Difficulty starting the engine
• Noticeable drop in acceleration

Can I change the spark plugs myself, or should I go to a mechanic?

Changing spark plugs is a relatively straightforward task that most car owners can do themselves.
However, if you’re not comfortable with basic engine maintenance or lack the necessary tools,
it’s recommended to consult a mechanic.

What is the recommended spark plug gap for Jeeps?

The spark plug gap for Jeeps can vary depending on the specific model and engine.
Refer to your Jeep’s owner’s manual or consult a trusted mechanic to determine the
correct spark plug gap for your vehicle.

Are there any precautions I should take while changing spark plugs?

Yes, here are a few precautions to keep in mind:

• Always disconnect the battery’s negative terminal before starting any work.
• Allow the engine to cool down completely before removing the spark plugs.
• Use dielectric grease to prevent moisture and aid in future removal.
• Double-check the torque specification when tightening the spark plugs
  to ensure they are neither over-tightened nor under-tightened.